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GANEX Newsletter No. 57 October 2017

III-N Technology

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METHODOLOGY

Each month

150+ new scientific publications

200+ new patent applications

30+ new press releases

Sources 10+ scientific journal editors

Elsevier, IOP, IEEE, Wiley, Springer, APS, AIP, AVS, ECS, Nature, Science …

10+ specialist magazines Semiconductor Today, ElectoIQ, i-micronews,

Compound Semiconductor, Solid State Technology … 5+ open access database: FreeFulPDF, DOAJ …

Patent database: Questel-Orbit

Selection by III-N French

experts

GANEX monthly newsletter

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TABLE OF CONTENTS (clickable links to chapters)

SCIENTIFIC PUBLICATIONS ............................................................................................................................. 4

GROUP 1 - LEDs and Lighting ................................................................................................................................. 4

GROUP 2 - Laser and Coherent Light ................................................................................................................... 14

GROUP 3 - Power Electronics .............................................................................................................................. 18

GROUP 4 - Advanced Electronics and RF ............................................................................................................. 30

GROUP 5 – MEMS and Sensors............................................................................................................................ 42

GROUP 6 - Photovoltaics and Energy harvesting................................................................................................. 49

GROUP 7 - Materials, Technology and Fundamental .......................................................................................... 52

PRESS RELEASE ............................................................................................................................................ 64

PATENT APPLICATIONS ................................................................................................................................ 99

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SCIENTIFIC PUBLICATIONS Selection of new scientific articles

GROUP 1 - LEDs and Lighting Group leader: Benjamin Damilano (CRHEA-CNRS)

Information selected by Benjamin Damilano (CRHEA-CNRS)

Dependencies of surface plasmon coupling effects on the p-GaN thickness of a thin-p-type light-emitting diode Institute of Photonics and Optoelectronics, and Department of Electrical Engineering, National Taiwan University, No. 1, Section 4, Roosevelt Road, Taipei 10617, Taiwan Optics Express https://doi.org/10.1364/OE.25.021526

The high performance of a light-emitting diode (LED) with the total p-type thickness as small as 38 nm is demonstrated. By increasing the Mg doping concentration in the p-AlGaN electron blocking layer through an Mg pre-flow process, the hole injection efficiency can be significantly enhanced. Based on this technique, the high LED performance can be maintained when the p-type layer thickness is significantly reduced. Then, the surface plasmon coupling effects, including the enhancement of internal quantum efficiency, increase in output intensity, reduction of efficiency droop, and increase of modulation bandwidth, among the thin p-type LED samples of different p-type thicknesses that are compared. These advantageous effects are stronger as the p-type layer becomes thinner. However, the dependencies of these effects on p-type layer thickness are different. With a circular mesa size of 10 μm in radius, through surface plasmon coupling, we achieve the record-high modulation bandwidth of 625.6 MHz among c-plane GaN-based LEDs. Quantification and analysis of color stability based on thermal transient behavior in white LED lamps IEM LED Lighting Technologies, 331 Newman Springs Rd., Suite 143, Red Bank, New Jersey 07701, USA Applied Optics https://doi.org/10.1364/AO.56.007539

We present measurement and analysis of color stability over time for two categories of white LED lamps based on their thermal management scheme, which also affects their transient lumen depreciation.

We previously reported that lumen depreciation in LED lamps can be minimized by properly designing the heat sink configuration that allows lamps to reach a thermal equilibrium condition quickly. Although it is well known that lumen depreciation degrades color stability of white light since color coordinates vary with total lumen power by definition, quantification and characterization of color shifts based on thermal transient behavior have not been previously reported in literature for LED lamps. Here we provide experimental data and analysis of transient color shifts for two categories of household LED lamps (from a total of six lamps in two categories) and demonstrate that reaching thermal equilibrium more quickly provides better stability for color rendering, color temperature, and less deviation of color coordinates from the Planckian blackbody locus line, which are all very important characterization parameters of color for white light. We report for the first time that a lamp’s color degradation from the turn-on time primarily depends on thermal transient behavior of the semiconductor LED chip, which experiences a wavelength shift as well as a decrease in its dominant wavelength peak value with time, which in turn degrades the phosphor conversion. For the first time, we also provide a comprehensive quantitative analysis that differentiates color degradation due to the heat rise in GaN/GaInN LED chips and subsequently the boards these chips are mounted on–from that caused by phosphor heating in a white LED module. Finally, we briefly discuss why there are some inevitable trade-offs between omnidirectionality and color and luminous output stability in current household LED lamps and what will help eliminate these trade-offs in future lamp designs. Enhanced output power of light-emitting diodes with embedded air-gap photonic crystals by nanosphere lithography Faculty of Information Technology, Beijing University of Technology, Beijing 100124, China, Beijing China College of Electronic Information and Control Engineering, Beijing University of Technology, Beijing China

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Semiconductor Lighting Technology Research and Development Center, Institute of Semiconductors, Chinese Academy of Sciences, beijing China Research and Development Center for Semiconductor Lighting, Institute of Semiconductors, Beijing, Beijing China Laboratory of Solid-State Light, Institute of Semiconductors, Chinese Academy of Sciences, Beijing, Beijing China Hebei University of Technology, 12606 Tianjin, Tianjin China Department of Chemistry, State Key Laboratory of New Ceramics and Fine Processing, Tsinghua University, Beijing 100084, China, Beijing China IEEE Photonics Journal https://doi.org/10.1109/JPHOT.2017.2750675

Large-scale two-dimensional air-gap photonic crystals (PhCs) were embedded in n-type GaN layer to enhance the light emission of GaN-based light-emitting diodes (LEDs). The embedded-PhCs were obtained through overgrowth on n-GaN templates, which had air holes array previously fabricated by using nanosphere lithography technology. The effects of the distance D from active region to PhCs on the light extraction efficiency (LEE) of LEDs are investigated by experiments and Finite Difference-Time Domain (FDTD) simulation. The PhCs LEDs with D = 2370 nm showed an improved light output power by 80.8% on average at forward current of 350 mA without degradation of electrical performance compared to conventional LEDs. It is mainly attributed to the improved LEE by enhancing the interaction of the guided modes and the embedded air-gap PhCs. Dynamics of carrier tunneling and recombination in asymmetric coupled InGaN multiple quantum wells Department of Electronic Engineering, East China Normal University, 500 Dongchuan Road, Shanghai 200241, China Department of Electronic Engineering, Xiamen University, 422 Siming South Road, Xiamen 361005, China Department of Advanced Materials Science, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561, Japan Optics Express https://doi.org/10.1364/OE.25.024745

In this work, dynamics of carrier tunneling and recombination in InGaN-based asymmetric coupled multiple quantum wells (AC-MQWs) are systematically studied by excitation power-dependent and temperature-dependent

photoluminescence (PL) measurements. With different pumping wavelengths of 405 and 325 nm, distinctly different PL spectral evolutions are observed, which could be well explained by the proposed anomalous carrier “reverse tunneling” based on the forbidden 1h→2e transitions in the AC-MQWs. The forbidden transitions are identified through the well agreement between the measured photo-modulated reflectance (PR) spectrum and the calculated interband transition energies. Our results indicate that, by ingeniously designing the MQW structure of the InGaN-based optoelectronic devices, it is possible to realize a specific interband optical transition which is even not allowed by the selection rule, and thereby effectively improve the carrier distribution across the QWs through the conventional and/or anomalous “reverse” carrier tunneling. Enhancing the Light-Extraction Efficiency of an AlGaN Nanowire Ultraviolet Light-Emitting Diode by Using Nitride/Air Distributed Bragg Reflector Nanogratings Photonics Laboratory, Computer, Electrical and Mathematical Sciences and Engineering Division, King Abdullah University of Science and Technology, Thuwal, Saudi Arabia National Center for Nanotechnology, King Abdulaziz City for Science and Technology, Riyadh, Saudi Arabia IEEE Photonics Journal https://doi.org/10.1109/JPHOT.2017.2749198

The performance and efficiency of AlGaN ultraviolet light-emitting diodes have been limited by the extremely low light-extraction efficiency (LEE) due to the intrinsic material properties of AlGaN. Here, to enhance the LEE of the device, we demonstrate an AlGaN nanowire light-emitting diode (NW-LED) integrated with nitride/air distributed Bragg reflector (DBR) nanogratings. Compared to a control device (only mesa), the AlGaN NW-LED with the nitride/air DBR nanogratings exhibits enhancement in the light output power and external quantum efficiency (EQE) by a factor of ∼1.67. The higher light output power and EQE are attributed mainly to the multiple reflectances laterally for the transverse magnetic (TM)-polarized light and scattering introduced by the nanogratings. To further understand the LEE enhancement, the electrical field distribution, extraction ratio, and polar pattern of the AlGaN NW-LED with and without the nitride/air DBR nanogratings were analyzed using the finite-difference time-domain method. It was observed that

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the TM-field emission was confined and scattered upward, whereas the polar pattern was intensified for the AlGaN NW-LED with the nanogratings. Our approach to enhance the LEE via the nitride/air DBR nanogratings can provide a promising route for increasing the efficiency of AlGaN-based LEDs, also, to functioning as facet mirror for AlGaN-based laser diodes. The degradation behaviors of white LEDs under highly accelerated stress testing (HAST) State Key Laboratory of Optoelectronic Materials and Technologies, School of electronics and information technology, Sun Vat-sen University, Guangzhou City, China Electronic Packaging Technology (ICEPT), 2017 18th International Conference on https://doi.org/10.1109/ICEPT.2017.8046559

Reliability of GaN-based LEDs is attracting researchers to engage in actively. At present, evaluating the lifetime of GaN-based LEDs in a short testing duration is still open question. Thermal and humidity stresses are two main environmental stresses that LED products will suffer infield applications. At the level of devices, LEDs are non-sensitive to vibration. In order to evaluate the reliabilities (including the lifetime and failure rate) of white LED devices in a short period, highly accelerated stress testing (HAST) method is attempted boldly in the present paper. A series of HAST conditions are designing through different combinations of thermal, electrical and humidity stresses. The temperatures fixed at 120°C, the biased currents vary between 20mA–350mA, and the humidities vary between 65%RH–95%RH, which imply the pressure inside the furnace is high than 1atm. The forward voltage and light intensity are monitored in-situ with a time step of 1min. Preliminary results indicate that the white LED devices' lifetime of L70 obeys Gaussian distribution under HAST humidity conditions, while the L70 lifetime obeys Inverse power distribution with the injection current density variation. Based on the Arrhenius equation, Inverse power law equation and Gauss equation, the copula acceleration model equation is established with respect to thermal, electrical and humidity stresses. As an example, under the condition of 20mA&85%RH&120°C the accelerating factor is estimated as 118.0 and 109.2. The general lifetime of L70 for white LED devices are estimated as 16926.9h and 5722.5h, respectively.

High-Performance GaN-Based LEDs on Si Substrates: The Utility of Ex Situ Low-Temperature AlN Template With Optimal Thickness State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou 510640, China Engineering Research Center on Solid-State Lighting and its Informationisation of Guangdong Province, South China University of Technology, Guangzhou 510640, China Department of Electronic Materials, School of Materials Science and Engineering, South China University of Technology, Guangzhou 510640, China IEEE Transactions on Electron Devices https://doi.org/10.1109/TED.2017.2753844

Ex situ low-temperature (LT)-AlN templates are employed to realize GaN-based light-emitting diodes (LEDs) on Si substrates by the combination of pulsed laser deposition and metal organic chemical vapor deposition. The influence of ex situ LT-AlN template thickness on the properties and performance of as-grown LEDs has been carefully studied. The LED wafer grown on 70-nm-thick ex situ LT-AlN template exhibits a crack-free surface, good crystalline quality, and excellent multiple quantum wells (MQWs) structural property. The 500 x 500 μm² LED chips fabricated with lateral structure show the highest light output power of 70.2 mW at an injection current of 300 mA. Through optimizing the thickness of ex situ LT-AlN template, the light output power is greatly improved by 39%. Theoretical analysis has been taken to study the enhancement mechanism of luminous intensity in this LED. It reveals that the residual stress in as-grown wafers is significant to enhance the luminescence of LEDs. The largest residual tensile stress in the LED presents great potential to enhance the carrier injection and transportation, increase the carrier concentrations, and improve the radiative recombination intensity in MQWs, which is crucial to improve the luminous intensity of LEDs. Enhancement of light emission and internal quantum efficiency in orange and red regions for regularly arrayed InGaN/GaN nanocolumns due to surface plasmon coupling Department of Engineering and Applied Sciences, Sophia University, 7-1, Kioi-cho, Chiyoda, Tokyo 102-8554, Japan Sophia Nanotechnology Research Center, Sophia University, 7-1, Kioi-cho, Chiyoda, Tokyo 102-8554, Japan

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Institute for Materials Chemistry and Engineering, Kyushu University, 744, Motooka Nishi-ku, Fukuoka 819-0395, Japan Appl. Phys. Lett. http://dx.doi.org/10.1063/1.5005517

We demonstrate enhanced light emission in the orange and red regions from regularly arrayed InGaN/GaN nanocolumns due to the surface plasmon (SP) coupling. A maximum photoluminescence (PL) enhancement ratio of 5.2 is observed by coating the nanocolumns with an Au thin film. In addition, a 2.1-fold increase in the internal quantum efficiency is obtained. Comparison of an electromagnetic field simulation and a theoretical calculation based on the SP dispersion indicates that the SP originates from a standing wave mode arising from the periodic Au/dielectric interface. The column-diameter dependence of the PL enhancement ratio can be reasonably explained by considering the simulated electric field intensity. The periodic plasmonic nanostructure is effective for improving the emission efficiencies of InGaN-based light emitters in the orange and red regions. Point defects controlling non-radiative recombination in GaN blue light emitting diodes: Insights from radiation damage experiments Department of Materials Science and Engineering, Korea University Anamro 145, Seoul 02841, South Korea National University of Science and Technology MISiS, Moscow, Leninskiy pr. 4, Moscow 119049, Russia Institute of Microelectronics Technology and High Purity Materials Russian Academy of Science, Chernogolovka, Moscow dist. 142432, Russia Department of Materials Science and Engineering, University of Florida, Gainesville, Florida 32611, USA Journal of Applied Physics http://dx.doi.org/10.1063/1.5000956

The role of Shockley-Read-Hall non-radiative recombination centers on electroluminescence (EL) efficiency in blue multi-quantum-well (MQW) 436 nm GaN/InGaN light emitting diodes (LEDs) was examined by controlled introduction of point defects through 6 MeV electron irradiation. The decrease in the EL efficiency in LEDs subjected to irradiation with fluences above 5 × 1015 cm−2 was closely correlated to the increase in concentration of Ec-0.7 eV electron traps in the active MQW region. This increase in trap density was accompanied by an increase in the both

diode series resistance and ideality factor (from 1.4 before irradiation to 2.1 after irradiation), as well as the forward leakage current at low forward voltages that compromise the injection efficiency. Hole traps present in the blue LEDs do not have a significant effect on EL changes with radiation because of their low concentration. Optimizing GaInN/GaN light-emitting diode structures under piezoelectric polarization Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, 110 8th Street, Troy, New York 12180, USA Department of Materials Science and Engineering, Rensselaer Polytechnic Institute, 110 8th Street, Troy, New York 12180, USA Journal of Applied Physics http://dx.doi.org/10.1063/1.5003251

We model and optimize various light emitting diode structures under bias voltage to maximize emission efficiency with particular respect to piezoelectric polarization. We compare polar and non-polar structures, namely, wurtzite c-plane, a-plane, (11–22) semi-polar, and (001) cubic crystal orientations in self-consistent Schrödinger-Poisson and drift-diffusion models. We consider both structures strained to a GaN pn-junction and strain-reduced systems based on GaInN templates. In light of numerous experimental findings of the actual electric field strength, we find it necessary to reduce the piezoelectric coefficients over those commonly cited. A weaker variation with composition or wavelength is the consequence. For the non-polar and cubic systems, we find a 22% increase of the electron-hole overlap and an 18% increase for the c-plane strain-reduced system at an InN fraction of x = 0.30 when compared to standard c-plane structures. For the green and longer wavelength range, we find that strain-reduced and cubic GaN systems should hold particular promise for higher radiative efficiency. Tunable InGaN quantum dot microcavity light emitters with 129 nm tuning range from yellow-green to violet Department of Electronic Engineering, Optoelectronics Engineering Research Center, Xiamen University, Xiamen 361005, China Department of Electronic Engineering, East China Normal University, Shanghai 200241, China Suzhou Institute of Nano-tech and Nano-bionics (SINANO), Chinese Academy of Sciences (CAS), Suzhou 215123, China

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Microsystem Technology Laboratory, Microsystem and Terahertz Research Center, China Academy of Engineering Physics, Chengdu 610200, Sichuan Province, China Appl. Phys. Lett. http://dx.doi.org/10.1063/1.4994945

An electrically pumped wavelength-tunable InGaN quantum dot (QD) based microcavity (MC) lighter emitter with a large tuning range of 129 nm was demonstrated. The multi-mode emission spectrum was tuned by injected current from 564 nm (yellow-green) to 435 nm (violet). The MC light emitter is featured with a double dielectric distributed Bragg reflector structure and a copper substrate fabricated using substrate transfer and laser lift off techniques. By utilizing an InGaN QD active layer with a tunable broad emission spectrum and a Fabry-Pérot cavity which allows multi-longitudinal mode resonating, the emission spectrum could be tuned among several particular cavity modes, which are decided by the gain enhancement factor. In addition, both the enhancement and suppression of MC emission modes caused by the gain enhancement factor were observed in a single MC device. As the first electrically driven III-V nitride semiconductor based tunable MC light emitter with a tuning range of 129 nm, the device is promising for applications such as in wide-gamut compact displays and projectors. Significant increase of quantum efficiency of green InGaN quantum well by realizing step-flow growth Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, University of Chinese Academy of Sciences, Suzhou 215123, People's Republic of China Key Laboratory of Nanodevices and Applications, Chinese Academy of Sciences, University of Chinese Academy of Sciences, Suzhou 215123, People's Republic of China Appl. Phys. Lett. http://dx.doi.org/10.1063/1.5001185

Two-dimensional (2D) island morphologies have been widely reported for green light-emitting InGaN quantum well (QW) layers, but the step-flow morphology has not been obtained for a green InGaN QW layer to date. In this Letter, we first investigate the cause of the 2D island morphology of green InGaN QWs via a comparison study with blue InGaN QWs. The short diffusion lengths of adatoms at low growth temperatures were found to be the cause of the 2D island morphology for the green InGaN QW. Step-flow growth of green InGaN QWs was obtained

by increasing the miscut angle of the c-plane GaN substrates from 0.20° to 0.48°, which reduces the atomic terrace width. Green InGaN/GaN multiple quantum wells (MQWs) with step-flow morphologies were found to have sharper well/barrier interfaces than MQWs with 2D island morphologies. The internal quantum efficiency of the green InGaN/GaN MQWs with the step-flow morphology is double that of the corresponding MQWs with the 2D island morphology at an excitation power density of 6.4 kW/cm2. Additionally, the emission linewidth of the green InGaN/GaN MQWs with the step-flow morphology is greatly reduced. As a result, the threshold currents of green laser diodes with larger miscut angles are greatly reduced. Impact of carrier localization on recombination in InGaN quantum wells and the efficiency of nitride light-emitting diodes: Insights from theory and numerical simulations Applied Physics Program, University of Michigan, 450 Church St, Ann Arbor, Michigan 48109, USA Electrical Engineering and Computer Science Department, University of Michigan, 1301 Beal Ave, Ann Arbor, Michigan 48109, USA Department of Physics, Temple University, 1925 N. 12th St, Philadelphia, Pennsylvania 19122, USA Materials Science and Engineering Department, University of Michigan, 2300 Hayward St, Ann Arbor, Michigan 48109, USA Appl. Phys. Lett. http://dx.doi.org/10.1063/1.5002104

We examine the effect of carrier localization due to random alloy fluctuations on the radiative and Auger recombination rates in InGaN quantum wells as a function of alloy composition, crystal orientation, carrier density, and temperature. Our results show that alloy fluctuations reduce individual transition matrix elements by the separate localization of electrons and holes, but this effect is overcompensated by the additional transitions enabled by translational symmetry breaking and the resulting lack of momentum conservation. Hence, we find that localization increases both radiative and Auger recombination rates, but that Auger recombination rates increase by one order of magnitude more than radiative rates. Furthermore, we demonstrate that localization has an overall detrimental effect on the efficiency-droop and green-gap problems of InGaN light-emitting diodes.

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Molecular beam epitaxial growth and characterization of AlN nanowall deep UV light emitting diodes Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, Michigan 48109, USA Department of Electrical and Computer Engineering, McGill University, 3480 University Street, Montreal, Quebec H3A 0E9, Canada Appl. Phys. Lett. http://dx.doi.org/10.1063/1.4989551

We have demonstrated large area AlN nanowall light emitting diodes grown on a sapphire substrate, which operate at 214 nm. Through detailed temperature-dependent and power-dependent photoluminescence measurements and rate equation analysis, a relatively high internal quantum efficiency (∼60%) was derived for AlN nanowall structures at room-temperature. A consistent blueshift in the emission wavelengths was measured with decreasing nanowall widths due to the reduced tensile strain distribution. The devices exhibit excellent current-voltage characteristics, including a turn-on voltage of 7 V and current densities of  >170 A/cm2 at 12 V. Effects of thickness ratio of InGaN to GaN in superlattice strain relief layer on the optoelectrical properties of InGaN-based green LEDs grown on Si substrates National Institute of LED on Si Substrate, Nanchang University, Nanchang 330096, China Journal of Applied Physics http://dx.doi.org/10.1063/1.5000134

InGaN-based multiple quantum well (MQW) green light-emitting diodes with a InGaN/GaN superlattice as a strain relief layer (SSRL) were grown on Si(111) substrates by metal organic chemical vapor deposition. The influences of the thickness ratio of InGaN to GaN in SSRL on the optoelectrical properties have been investigated. Electrical measurements show that the sample with a higher thickness ratio has a lower series resistance. This is mainly ascribed to the improvement of carrier vertical transport due to the thinner GaN in SSRL. However, it is found that the leakage current increases with the thickness ratio from 1:1 to 2.5:1, which could be attributed to the larger density of small size V-pits forming at the first few QW pairs. Compared with the smaller thickness ratio, the sample with a higher thickness ratio of

InGaN to GaN in SSRL is found to exhibit larger strain relaxation (about 33.7%), but the electroluminescence measurement exhibits inferior emission efficiency. Carrier leakage via the small V-pits and the rougher interface of MQW are believed to be responsible for the reduction of emission efficiency. Influence of the heterostructure design on the optical properties of GaN and Al0.1Ga0.9N quantum dots for ultraviolet emission Université Côte d'Azur, CNRS, CRHEA, 06560 Valbonne, France Université Montpellier 2, L2C, UMR 5221, 34095 Montpellier Cedex 5, France CNRS-CRHEA, Rue B. Gregory, 06560 Valbonne, France Journal of Applied Physics http://dx.doi.org/10.1063/1.5000238

The optical properties of AlyGa1-yN quantum dots (QDs), with y = 0 or y = 0.1, in an AlxGa1−xN matrix are studied. The influence of the QD layer design is investigated pointing out the correlations between the QD structural and optical properties. In a first part, the role of the epitaxial strain in the dot self-assembling process is studied by fabricating GaN QD layers on different AlxGa1−xN layers with 0.5 ≤ x ≤ 0.7. Photoluminescence (PL) measurements show the main influence of the increase of the internal electric field (Fint) on the QD optical response inducing a strong red shift in the emission energy as x increases. Time resolved combined with temperature dependent PL measurements enabled the estimation of the QD internal quantum efficiencies at low temperature showing values around 50%. In addition, a PL integrated intensity ratio up to 74% is shown, between 300 and 9 K. In the second part, the design of Al0.1Ga0.9N QDs was investigated, by varying the Al0.1Ga0.9N amount deposited. An increase of the transition energy (from 3.65 eV up to 3.83 eV) is obtained while decreasing the deposited amount. Calculations of the ground state transition energies as a function of the Al0.1Ga0.9N dot height give a value of Fint around 2.0 ± 0.5 MV/cm. Therefore, the propensity of Al0.1Ga0.9N dots to emit at much higher energies than GaN dots (a PL shift of ∼1 eV using a low excitation power) is seen as the consequence of the reduced Fint together with their smaller sizes.

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Deep-UV emission at 219 nm from ultrathin MBE GaN/AlN quantum heterostructures Department of Electrical and Computer Engineering, Cornell University, Ithaca, New York 14853, USA Notre Dame Integrated Imaging Facility, University of Notre Dame, Notre Dame, Indiana 46556, USA Department of Electrical Engineering, University of Notre Dame, Notre Dame, Indiana 46556, USA Department of Materials Science and Engineering, Cornell University, Ithaca, New York 14853, USA Kavli Institute at Cornell for Nanoscale Science, Cornell University, Ithaca, New York 14853, USA Appl. Phys. Lett. http://dx.doi.org/10.1063/1.5000844

Deep ultraviolet (UV) optical emission below 250 nm (∼5 eV) in semiconductors is traditionally obtained from high aluminum containing AlGaN alloy quantum wells. It is shown here that high-quality epitaxial ultrathin binary GaN quantum disks embedded in an AlN matrix can produce efficient optical emission in the 219–235 nm (∼5.7–5.3 eV) spectral range, far above the bulk bandgap (3.4 eV) of GaN. The quantum confinement energy in these heterostructures is larger than the bandgaps of traditional semiconductors, made possible by the large band offsets. These molecular beam epitaxy-grown extreme quantum-confinement GaN/AlN heterostructures exhibit an internal quantum efficiency of 40% at wavelengths as short as 219 nm. These observations together with the ability to engineer the interband optical matrix elements to control the direction of photon emission in such binary quantum disk active regions offer unique advantages over alloy AlGaN quantum well counterparts for the realization of deep-UV light-emitting diodes and lasers. High-Efficiency InGaN/GaN Quantum Well-Based Vertical Light-Emitting Diodes Fabricated on β-Ga2O3 Substrate King Abdullah University of Science and Technology (KAUST), Physical Sciences and Engineering Division, Thuwal 23955-6900, Saudi Arabia King Abdullah University of Science and Technology (KAUST), Imaging and Characterization Core Lab, Thuwal 23955-6900, Saudi Arabia Tamura Corporation and Novel Crystal Technology, Inc., Sayama, Saitama 350-1328, Japan ACS Appl. Mater. Interfaces http://dx.doi.org/10.1021/acsami.7b09584

We demonstrate a state-of-the-art high-efficiency GaN-based vertical light-emitting diode (VLED) grown on a transparent and conductive (−201)-oriented (β-Ga2O3) substrate, obtained using a straightforward growth process that does not require a high-cost lift-off technique or complex fabrication process. The high-resolution scanning transmission electron microscopy (STEM) images confirm that we produced high quality upper layers, including a multiquantum well (MQW) grown on the masked β-Ga2O3 substrate. STEM imaging also shows a well-defined MQW without InN diffusion into the barrier. Electroluminescence (EL) measurements at room temperature indicate that we achieved a very high internal quantum efficiency (IQE) of 78%; at lower temperatures, IQE reaches ∼86%. The photoluminescence (PL) and time-resolved PL analysis indicate that, at a high carrier injection density, the emission is dominated by radiative recombination with a negligible Auger effect; no quantum-confined Stark effect is observed. At low temperatures, no efficiency droop is observed at a high carrier injection density, indicating the superior VLED structure obtained without lift-off processing, which is cost-effective for large-scale devices. Managing Green Emission in Coupled InGaN QW–QDs Nanostructures via Nanoengineering Department of Physics, ‡Shenzhen Institute of Research and Innovation (HKU-SIRI), and §HKU-CAS Joint Laboratory on New Materials, The University of Hong Kong, Pokfulam Road, Hong Kong, China Tsinghua National Laboratory for Information Science and Technology, Department of Electronic Engineering, Tsinghua University, Beijing 100084, China Department of Physics, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China J. Phys. Chem. C http://dx.doi.org/10.1021/acs.jpcc.7b07826

By utilizing and designing coupled InGaN QW–QDs nanostructures as active layer, we show a demonstration of significant enhancement of green emission in the hybrid nanostructure with a 4.5 nm GaN barrier layer at high temperatures. Such enhancement is ascribed to temperature-dependent phonon-assisted tunneling of excitons from QW to QDs and suppression of nonradiative recombination of excitons localized in the QDs layer in the sample with a 4.5 nm barrier layer. This study shall be useful for optimization design of high-efficiency InGaN-based green LEDs and also could shed some light on

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the complicated internal luminescence mechanisms in InGaN QW–QDs hybrid nanostructures. Fabrication of Phosphor-Free III-Nitride Nanowire Light-Emitting Diodes on Metal Substrates for Flexible Photonics Department of Electrical and Computer Engineering and ⊥Electronic Imaging Center, New Jersey Institute of Technology, 323 Martin Luther King Boulevard, University Heights, Newark, New Jersey 07102, United States Epitaxial Laboratory Inc., Tiana Place, Dix Hills, New York 11746, United States Vietnam Academy of Science and Technology, Institute of Applied Materials Science, 1 Mac Dinh Chi Street, District 1, Ho Chi Minh City 70001, Vietnam Faculty of Science and Technology, Hoa Sen University, 8 Nguyen Van Trang Street, District 1, Ho Chi Minh City 70001, Vietnam ACS Omega http://dx.doi.org/10.1021/acsomega.7b00843

In this paper, we report our study on high-performance III-nitride nanowire light-emitting diodes (LEDs) on copper (Cu) substrates via the substrate-transfer process. Nanowire LED structures were first grown on silicon-on-insulator (SOI) substrates by molecular beam epitaxy. Subsequently, the SOI substrate was removed by combining dry- and wet-etching processes. Compared to conventional nanowire LEDs on Si, the nanowire LEDs on Cu exhibit several advantages, including more efficient thermal management and enhanced light-extraction efficiency (LEE) because of the usage of metal reflectors and highly thermally conductive metal substrates. The LED on Cu, therefore, has stronger photoluminescence, electroluminescence intensities, and better current–voltage characteristics compared to the conventional nanowire LED on Si. Our simulation results further confirm the improved device performance of LEDs on Cu, compared to LEDs on Si. The LEE of the nanowire LED on Cu is nine times higher than that of the LED on Si at the same nanowire radius of 60 nm and spacing of 130 nm. Moreover, by engineering the device-active region, we achieved high-brightness phosphor-free LEDs on Cu with highly stable white-light emission and high color-rendering index of ∼95, showing their promising applications in general lighting, flexible displays, and wearable applications.

444 nm InGaN light emitting diodes on low-defect-density $(11\bar22)$ GaN templates on patterned sapphire Materials Department, University of California, Santa Barbara, CA 93106, U.S.A. Department of Electrical and Computer Engineering, University of California, Santa Barbara, CA 93117, U.S.A. Université Côte d'Azur, CNRS–CRHEA, 06560 Valbonne, France Applied Physics Express https://doi.org/10.7567/APEX.10.106501

Efficient InGaN-based 444 nm blue light-emitting diodes (LEDs) were fabricated on low-defect-density $(11-22)$ semipolar GaN templates grown on patterned r-sapphire. At 20 A/cm2, the packaged $(11-22)$ LEDs exhibited a light output power of 2.9 mW (17.8 mW at 100 A/cm2) and a record peak external quantum efficiency of 6.4% showing a negligible efficiency droop and blue shift with drive currents up to 100 A/cm2. In addition, we demonstrated light extraction simulations for the $(11-22)$ template, which showed that the structured pattern is not only beneficial for limiting the defect propagation but also increases the light extraction by 29% compared with GaN layers grown on planar substrates. Ag/SiO2 nanoparticle-based plasmonic enhancement of light output in nanohole-patterned InGaN/GaN blue light-emitting diodes Department of Materials Science and Engineering, Korea University, Seoul 02841, Korea School of Advanced Materials Engineering and Research Center of Advanced Materials Development, Chonbuk National University, Jeonju 561-756, Korea Department of Optical Engineering, Kongju National University, Cheonan 331-717, Korea Department of Semiconductor Electronics and Semiconductor Physics, National University of Science and Technology MISiS, 119049 Moscow, Russia Japanese Journal of Applied Physics https://doi.org/10.7567/JJAP.56.100305

Improved performance of blue InGaN/GaN light-emitting diodes (LEDs) is realized as a result of fabricating nanohole patterns in the p-GaN contact layer and embedding the nanoholes with Ag/SiO2 nanoparticles to generate localized surface plasmons (LSPs). Good matching between LSP resonance energy and LED emission energy together with the close proximity between nanoparticles and the active

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region results in strong coupling between them. Consequently, the photoluminescence and electroluminescence intensities increased to 1.75 and 1.10, respectively, compared with nanohole patterned reference LEDs. Simultaneous determination of defect distributions and energies near InGaN/GaN quantum wells by capacitance–voltage measurement Department of Physics, Kongju National University, Gongju, Chungnam 32588, Republic of Korea UJL Ltd, Siheung, Gyeonggi 15101, Republic of Korea Department of Materials Science and Engineering, Chungnam University, Daejeon 34134, Republic of Korea Journal of Physics D: Applied Physics https://doi.org/10.1088/1361-6463/aa81f2

The distributions, densities and energies of defects near InGaN/GaN quantum wells in blue light-emitting diodes were simultaneously determined by utilizing capacitance–voltage (C–V) measurements. By combining the modulation frequency dependency, temperature dependency and C–V depth profiling with additional laser illumination, the densities and the locations of the defective layers could be determined. The relative defect densities of the devices were directly compared by monitoring the magnitude of the frequency dependence. This frequency dependency varies distinctly as the sample temperature changes. The activation energies of defects are then determined by analyzing the frequency dependency of C–V with temperature. We found that three different defects states were formed in a low-temperature-grown un-doped GaN (LT-GaN) layer inserted under the active layer. The activation energies of those defects were determined to be 3.96, 12.1 and 45.9 meV. The formation of additional defects states in the active layers induced by the insertion of LT-GaN layer was also observed. Optoelectronic device physics and technology of nitride semiconductors from the UV to the terahertz Department of Electrical and Computer Engineering, Division of Materials Science and Engineering, Photonics Center, Boston University, Boston, MA 02215, United States of America Reports on Progress in Physics https://doi.org/10.1088/1361-6633/aa7bb2

This paper reviews the device physics and technology of optoelectronic devices based on semiconductors

of the GaN family, operating in the spectral regions from deep UV to Terahertz. Such devices include LEDs, lasers, detectors, electroabsorption modulators and devices based on intersubband transitions in AlGaN quantum wells (QWs). After a brief history of the development of the field, we describe how the unique crystal structure, chemical bonding, and resulting spontaneous and piezoelectric polarizations in heterostructures affect the design, fabrication and performance of devices based on these materials. The heteroepitaxial growth and the formation and role of extended defects are addressed. The role of the chemical bonding in the formation of metallic contacts to this class of materials is also addressed. A detailed discussion is then presented on potential origins of the high performance of blue LEDs and poorer performance of green LEDs (green gap), as well as of the efficiency reduction of both blue and green LEDs at high injection current (efficiency droop). The relatively poor performance of deep-UV LEDs based on AlGaN alloys and methods to address the materials issues responsible are similarly addressed. Other devices whose state-of-the-art performance and materials-related issues are reviewed include violet-blue lasers, 'visible blind' and 'solar blind' detectors based on photoconductive and photovoltaic designs, and electroabsorption modulators based on bulk GaN or GaN/AlGaN QWs. Finally, we describe the basic physics of intersubband transitions in AlGaN QWs, and their applications to near-infrared and terahertz devices. Enhancing light coupling and emission efficiencies of AlGaN thin film and AlGaN/GaN multiple quantum wells with periodicity-wavelength matched nanostructure array Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo 315201, China Semiconductor Lighting Technology Research and Development Center, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China Department of Electrical and Electronic Engineering, Faculty of Science and Engineering, The University of Nottingham Ningbo China, China Nanoscale http://dx.doi.org/10.1039/C7NR04341D

Poor light extraction efficiency (LEE) has been one of the major challenges responsible for the low external quantum efficiency of AlGaN-based ultraviolet light emitting Diodes (UV-LEDs). In this study, AlGaN nanostructure arrays were fabricated using a large-

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scale nanosphere self-assembly technique followed by reactive ion etching, and the transmission property of the AlGaN thin film and the photoluminescence (PL) behavior of AlGaN/GaN multiple-quantum-wells (MQWs) were investigated. A 90% light transmission value was obtained for the AlGaN thin film and a 2.5-fold increase in the band edge luminescence of the MQWs were obtained with an optimized nanostructure periodicity. Essentially, a general rule of periodicity-MQW emission wavelength matching criteria-was provided. Both the light transmission properties of the Al0.55Ga0.45N/AlN/sapphire thin film and the photoluminescence (PL) behavior of the AlGaN/GaN MQWs contribute to an improved understanding of the light extraction mechanism of PhC patterned UV-LEDs. Raman spectra also demonstrated the strain relaxation inside the MQW after nanostructure fabrication and thermal annealing. This study provides a pathway towards higher efficiency UV-LEDs with the help of a periodicity-wavelength matched nanostructure array. AlN/GaN Digital Alloy for Mid- and Deep-Ultraviolet Optoelectronics Center for Photonics and Nanoelectronics, Department of Electrical and Computer Engineering, Lehigh University, Bethlehem, PA, 18015, USA Department of Electrical and Computer Engineering, Clarkson University, Potsdam, NY, 13699, USA Scientific Reports http://dx.doi.org/10.1038/s41598-017-12125-9

The AlN/GaN digital alloy (DA) is a superlattice-like nanostructure formed by stacking ultra-thin ( ≤ 4 monolayers) AlN barriers and GaN wells periodically. Here we performed a comprehensive study on the electronics and optoelectronics properties of the AlN/GaN DA for mid- and deep-ultraviolet (UV) applications. Our numerical analysis indicates significant miniband engineering in the AlN/GaN DA by tuning the thicknesses of AlN barriers and GaN wells, so that the effective energy gap can be engineered from ~3.97 eV to ~5.24 eV. The band structure calculation also shows that the valence subbands of the AlN/GaN DA is properly rearranged leading to the heavy-hole (HH) miniband being the top valence subband, which results in the desired transverse-electric polarized emission. Furthermore, our study reveals that the electron-hole wavefunction overlaps in the AlN/GaN DA structure

can be remarkably enhanced up to 97% showing the great potential of improving the internal quantum efficiency for mid- and deep-UV device application. In addition, the optical absorption properties of the AlN/GaN DA are analyzed with wide spectral coverage and spectral tunability in mid- and deep-UV regime. Our findings suggest the potential of implementing the AlN/GaN DA as a promising active region design for high efficiency mid- and deep-UV device applications.

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GROUP 2 - Laser and Coherent Light Group leader: Bruno Gayral (CEA)

Information selected by Knowmade

Efficient second harmonic generation in low-loss planar GaN waveguides Université Côte d’Azur, CNRS, CRHEA, rue Bernard Grégory, 06560 Valbonne, France Université Côte d’Azur, CNRS, INΦNI, Parc Valrose, 06100 Nice, France Centre de Nanosciences et de Nanotechnologies, CNRS, Univ. Paris-Sud, Université Paris-Saclay, Bâtiment 220, Rue André Ampère, F-91405 Orsay, France Université Grenoble Alpes, CEA, LETI, MINATEC Campus, F-38054 Grenoble, France Optics Express https://doi.org/10.1364/OE.25.023035

We demonstrate low-loss GaN/AlGaN planar waveguides grown by molecular beam epitaxy on sapphire substrates. By using a proper AlGaN cladding layer and reducing surface roughness we reach <1dB/cm propagation losses at 633nm. These low propagation losses allow an efficient second harmonic generation using modal phase matching between a TM0 pump at 1260nm and a TM2 second harmonic at 630nm. A maximal power conversion of 2% is realized with an efficiency of 0.15%·W−1cm−2. We provide a modelling that demonstrates broadband features of GaN/AlGaN platform by showing second harmonic wavelengths tunability from the visible up to the near-infrared spectral region. We discuss drawbacks of modal phase matching and propose a novel solution which allows a drastic improvement of modal overlaps with the help of a planar polarity inversion. This new approach is compatible with low propagation losses and may allow as high as 100%·W−1cm−2 conversion efficiencies in the future. Demonstration of continuous-wave second and third harmonic generation in high-Q gallium nitride photonic crystal cavities Institut de Physique, Ecole Polytechnique Fédérale de Lausanne (EPFL), Switzerland Dipartimento di Fisica “A. Volta,” Università di Pavia, Italy Transparent Optical Networks (ICTON), 2017 19th International Conference on https://doi.org/10.1109/ICTON.2017.8024780

Wide bandgap semiconductors such as gallium nitride (GaN) are essential constituents of future optical circuits, as their optical response can accommodate a broad wavelength range while suppressing two-photon absorption and free-carrier absorption effects that are encountered with silicon (Si) structures. Their direct wide bandgap is also favourable for the incorporation of active elements. Furthermore, nonlinear optical processes can be harnessed by exploiting the higher-order susceptibility tensors of the crystal structure to achieve advanced light control modalities, enabling all-optical processing and the generation of entangled photon states. We will report on nonlinear frequency conversion from the telecom range via second harmonic generation (SHG) and third harmonic generation (THG) in suspended gallium nitride slab photonic crystal (PhC) cavities on silicon, under continuous-wave resonant excitation. Genetic optimization is applied to sweep parameter space for the highest cavity quality factors, and simultaneously accounting for power in-coupling. While there is a clear trade-off theoretically between coupling efficiency and Q-factor for a given cavity design, the upper limit on the Q-factor that is imposed by loss channels, given the disorder figure of current fabrication technology, makes room for introducing improved far-field coupling to enhance nonlinear processes without sacrificing the experimentally achievable light confinement. Far-field coupling is addressed through various PhC cavity designs, which enable the excitation of the fundamental mode with a Gaussian beam. Optimized two-dimensional PhC cavities with increased far-field coupling have been characterized with quality factors as high as 44′000, approaching the computed theoretical values. The strong enhancement in light confinement has enabled second harmonic generation (SHG) under continuous-wave excitation, with up-conversion from both 1300 nm and 1550 nm wavelength bands, confirmed by spectral and power dependence measurements. At 1550 nm, normalized SHG conversion efficiency as large as 2.4×10−3 W−1 are measured as well as simultaneous THG. SHG emission power of up to 0.74 nW has been detected without saturation

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Improving emission uniformity and linearizing band dispersion in nanowire arrays using quasi-aperiodicity Sandia National Laboratories, P.O. Box 5800, Albuquerque, NM 87185, USA Ming Hsieh Department of Electrical Engineering, University of Southern California, Los Angeles, CA 90089, USA Optical Materials Express https://doi.org/10.1364/OME.7.003634

We experimentally investigate a new class of quasi-aperiodic structures for improving the emission pattern in nanowire arrays. Efficient normal emission, as well as lasing, can be obtained from III-nitride photonic crystal (PhC) nanowire arrays that utilize slow group velocity modes near the Γ-point in reciprocal space. However, due to symmetry considerations, the emitted far-field pattern of such modes are often ‘donut’-like. Many applications, including lighting for displays or lasers, require a more uniform beam profile in the far-field. Previous work has improved far-field beam uniformity of uncoupled modes by changing the shape of the emitting structure. However, in nanowire systems, the shape of nanowires cannot always be arbitrarily changed due to growth or etch considerations. Here, we investigate breaking symmetry by instead changing the position of emitters. Using a quasi-aperiodic geometry, which changes the emitter position within a photonic crystal supercell (2x2), we are able to linearize the photonic bandstructure near the Γ-point and greatly improve emitted far-field uniformity. We realize the III-nitride nanowires structures using a top-down fabrication procedure that produces nanowires with smooth, vertical sidewalls. Comparison of room-temperature micro-photoluminescence (µ-PL) measurements between periodic and quasi-aperiodic nanowire arrays reveal resonances in each structure, with the simple periodic structure producing a donut beam in the emitted far-field and the quasi-aperiodic structure producing a uniform Gaussian-like beam. We investigate the input pump power vs. output intensity in both systems and observe the simple periodic array exhibiting a non-linear relationship, indicative of lasing. We believe that the quasi-aperiodic approach studied here provides an alternate and promising strategy for shaping the emission pattern of nanoemitter systems.

Red and Near-Infrared III-Nitride Quantum Dot Lasers Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, Ann Arbor, Michigan United States Electrical and Computer Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois United States IEEE Journal of Selected Topics in Quantum Electronics https://doi.org/10.1109/JSTQE.2017.2754368

InGaN/GaN self-organized quantum dots and similar dots in GaN nanowires are formed by strain relaxation and the luminescence from these nanostructures extend to longer wavelengths than generally obtained with quantum wells. We have exploited this advantage by incorporating these nanostructures in the gain region of edge-emitting diode lasers. Here we describe the characteristics of 650nm self-organized quantum dot lasers epitaxially grown on GaN and 1.3μm dot-in-nanowire array lasers grown on (001)Si by molecular beam epitaxy. The devices are characterized by relatively low threshold currents, excellent temperature stability (T0 > 200K) and differential gain ~10−16cm2. The highest measured small-signal modulation bandwidth of the dot-in-nanowire laser is 3.3GHz. The experiments have been complemented by theoretical modeling of the self-organized quantum dots and lasers made with them. These new classes of devices open up new opportunities in applications such as displays, optical data storage, heads-up displays in automobiles, plastic fiber communication, and silicon photonics. Optically-pumped Single-mode Deep-ultraviolet Microdisk Lasers with AlGaN-based Multiple Quantum Wells on Si Substrate Department of Electrical Engineering and Computer Science, Northwestern University, Evanston, Illinois United States University of California Santa Barbara, 8786 Santa Barbara, California United States Semiconductor Lighting Technology Research and Development Center, Institute of Semiconductors, Chinese Academy of Sciences, Beijing China Institute of Semiconductors, Chinese Academy of Sciences, Semiconductor Lighting Technology Research and Development Center, Beijing China Research and Development Center for Semiconductor Lighting, Institute of Semiconductors, CAS, Peking, None Selected China IEEE Photonics Journal https://doi.org/10.1109/JPHOT.2017.2752207

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In this work, we report demonstration of optically-pumped single-mode deep-ultraviolet lasing actions operating at room temperature from ~1-μm 150nm-thick undercut microdisks with AlN/Al0.35Ga0.65N (5.5nm/2.5nm) multiple quantum wells (MQWs). These AlGaN-based microdisks are grown on Si substrate by metal-organic chemical vapor deposition (MOCVD). The lasing wavelength centers at ~300.1nm with the linewidth of ~1.0nm as the excitation exceeds the lasing threshold of ~24.2 mJ/cm2. An emission coupling factor (β) of 9.2×10-2 is estimated based on the light output characteristics of the AlN/AlGaN microdisks with increasing the pumping densities. Concurrently, a 100meV blue-shift in the mode energy has also been observed. The lasing spectral peak is attributed to fundamental-order transverse-electric (TE) whispering-gallery modes (WGMs), confirmed by three-dimensional (3D) finite-difference time-domain (FDTD) simulations. GaN microring waveguide bonded to Si substrate by polymer Department of Finemechanics, Tohoku University, Sendai 980-8579, Japan Optical MEMS and Nanophotonics (OMN), 2017 International Conference on https://doi.org/10.1109/OMN.2017.8051464

Hybrid integration of GaN and Si photonic devices is promising. Using a polymer bonding technique, GaN microring resonators are fabricated on Si substrate. Transmission characteristics of the GaN microring is measured. Q factor limitation at short wavelength (around 300 nm) in III-nitride-on-silicon photonic crystal cavities Centre de Nanosciences et de Nanotechnologies, CNRS, Univ. Paris-Sud, Université Paris-Saclay, F-91405 Orsay, France CEA, INAC-PHELIQS, Nanophysique et Semiconducteurs Group, F-38000 Grenoble, France Laboratoire Charles Coulomb (L2C), UMR 5221 CNRS-Université de Montpellier, F-34095 Montpellier, France Université Côte d'Azur, CRHEA-CNRS, F-06560 Valbonne, France Univ. Grenoble Alpes, F-38000 Grenoble, France Appl. Phys. Lett. http://dx.doi.org/10.1063/1.4997124

III-nitride-on-silicon L3 photonic crystal cavities with resonances down to 315 nm and quality factors (Q)

up to 1085 at 337 nm have been demonstrated. The reduction of the quality factor with decreasing wavelength is investigated. Besides the quantum well absorption below 340 nm, a noteworthy contribution is attributed to the residual absorption present in thin AlN layers grown on silicon, as measured by spectroscopic ellipsometry. This residual absorption ultimately limits the Q factor to around 2000 at 300 nm when no active layer is present. Deep-UV emission at 219 nm from ultrathin MBE GaN/AlN quantum heterostructures Department of Electrical and Computer Engineering, Cornell University, Ithaca, New York 14853, USA Notre Dame Integrated Imaging Facility, University of Notre Dame, Notre Dame, Indiana 46556, USA Department of Electrical Engineering, University of Notre Dame, Notre Dame, Indiana 46556, USA Department of Materials Science and Engineering, Cornell University, Ithaca, New York 14853, USA Kavli Institute at Cornell for Nanoscale Science, Cornell University, Ithaca, New York 14853, USA Appl. Phys. Lett. http://dx.doi.org/10.1063/1.5000844

Deep ultraviolet (UV) optical emission below 250 nm (∼5 eV) in semiconductors is traditionally obtained from high aluminum containing AlGaN alloy quantum wells. It is shown here that high-quality epitaxial ultrathin binary GaN quantum disks embedded in an AlN matrix can produce efficient optical emission in the 219–235 nm (∼5.7–5.3 eV) spectral range, far above the bulk bandgap (3.4 eV) of GaN. The quantum confinement energy in these heterostructures is larger than the bandgaps of traditional semiconductors, made possible by the large band offsets. These molecular beam epitaxy-grown extreme quantum-confinement GaN/AlN heterostructures exhibit an internal quantum efficiency of 40% at wavelengths as short as 219 nm. These observations together with the ability to engineer the interband optical matrix elements to control the direction of photon emission in such binary quantum disk active regions offer unique advantages over alloy AlGaN quantum well counterparts for the realization of deep-UV light-emitting diodes and lasers.

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Collective Lasing Behavior of Monolithic GaN–InGaN Core–Shell Nanorod Lattice under Room Temperature Department of Photonics and Institute of Electro-Optical Engineering, National Chiao Tung University, 1001 Ta Hsueh Road, Hsinchu 300, Taiwan Nano Lett. http://dx.doi.org/10.1021/acs.nanolett.7b02922

We demonstrated a monolithic GaN–InGaN core–shell nanorod lattice lasing under room temperature. The threshold pumping density was as low as 140 kW/cm2 with a quality factor as high as 1940. The narrow mode spacing between lasing peaks suggested a strong coupling between adjacent whisper gallery modes (WGM), which was confirmed with the far-field patterns. Excitation area dependent photoluminescence revealed that the long-wavelength lasing modes dominated the collective lasing behavior under a large excitation area. The excitation-area-dependent lasing behavior resulted from the prominent optical coupling among rods. According to the optical mode simulations and truncated-rod experiments, we confirmed that the fine-splitting of lasing peaks originated from the coupled supermodes existing in the periodic nanorod lattices. With wavelength-tunable active materials and a wafer-level scalable processing, patterning optically coupled GaN–InGaN core–shell nanorods is a highly practical approach for building various on-chip optical components including emitters and coupled resonator waveguides in visible and ultraviolet spectral range. Internal power loss in GaN-based lasers: mechanisms and remedies NUSOD Institute LLC, Newark, USA Optical and Quantum Electronics https://doi.org/10.1007/s11082-017-1166-5

GaN-based laser diodes transform only a relatively small fraction of the electrical input power into laser light. The inherently large series resistance of these devices causes significant self-heating that leads to the typical power roll-off at high current. We analyze recently reported measurements using advanced numerical laser simulation and investigate the physical mechanisms that limit the lasing power in continuous-wave operation. Contrary to common expectations, our analysis reveals a strong influence

of Auger recombination since the self-heating leads to a rising quantum well carrier density above the lasing threshold. As possible remedy, we investigate the effect of a tunnel-junction contact and predict a significant enhancement of lasing power and efficiency. Effect of Droop Phenomenon in InGaN/GaN Blue Laser Diodes on Threshold Current Department of Physics, Shanghai University, Shanghai 200444 Suzhou Institute of Nano-tech and Nano-bionics, University of Chinese Academy of Sciences, Suzhou 215123 Key Laboratory of Nanodevice and Applications, Chinese Academy of Sciences, Suzhou 215123 Chinese Physics Letters https://doi.org/10.1088/0256-307X/34/9/097801

Electroluminescence (EL) and temperature-dependent photoluminescence measurements are performed to study the internal quantum efficiency droop phenomenon of blue laser diodes (LDs) before lasing. Based on the ABC mode, the EL result demonstrates that non-radiative recombination rates of LDs with threshold current densities of 4 and 6 kA/cm2 are similar, while LD with threshold current density of 4 kA/cm2 exhibits a smaller auger-like recombination rate compared with the one of 6 kA/cm2. The internal quantum efficiency droop is more serious for LD with higher threshold current density. The internal quantum efficiency value estimated from temperature-dependent photoluminescence is consistent with EL measurements.

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GROUP 3 - Power Electronics Group leader: Frédéric Morancho (LAAS-CNRS)

Information selected by Frédéric Morancho (LAAS-CNRS) and Yvon Cordier (CRHEA-CNRS)

Impact of trench dimensions on the device performance of GaN vertical trench MOSFETs University of California at Santa Barbara, Santa Barbara, CA 93106 USA. University of California at Davis, Davis, CA 93106 USA. IEEE Electron Device Letters https://doi.org/10.1109/LED.2017.2749540

In this study, we have examined the impact of trench dimensions on the breakdown voltage and on-resistance of trench MOSFETs fabricated on sapphire and bulk GaN substrates. Contrary to simulation studies, the breakdown voltage decreased with an increase in trench dimensions in devices fabricated on sapphire substrates. However, such breakdown voltage dependence with trench dimensions was not observed in devices fabricated on bulk GaN substrates of the same area. The observed trend on GaN on sapphire devices was associated with the equivalently reduced number of dislocations per device area. These results gives an insight into how dislocations could affect breakdown voltage in power MOSFETs. Breakdown Enhancement and Current Collapse Suppression by High-Resistivity GaN Cap Layer in Normally-Off AlGaN/GaN HEMTs School of Materials Science and Engineering, Nanjing University of Science and Technology, Xiao Ling Wei 200, Nanjing 210094, China China Key Laboratory of Nanodevices and Applications, Suzhou Institute of Nano-tech and Nano-bionics, CAS, Suzhou 215123, China State Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science and Technology of China, Chengdu, 610054, China IEEE Electron Device Letters https://doi.org/10.1109/LED.2017.2749678

In this paper, a device structure of high-resistivity-cap-layer HEMT (HRCL-HEMT) is developed for normally-off p-GaN gate HEMT toward high breakdown voltage and low current collapse. It demonstrates that the breakdown capability and current collapse of the device were effectively improved due to the introduction of a thick HR-GaN cap layer. The fabricated HRCL-HEMT exhibits a high

breakdown voltage of 1020 V at IDS = 10 μA/mm with the substrate grounded. Meanwhile, the dynamic Ron is only 2.4 times the static Ron after off-state VDS stress of 1000 V with the substrate grounded (the OFF to ON switching time interval is set to 200 μs). Characterisation and Modelling of Gallium Nitride Power Semiconductor Devices Dynamic On-state Resistance Electrical and Electronic Engineering, University of Nottingham, Nottingham United Kingdom of Great Britain and Northern Ireland Electrical and Electronic, University of Nottingham, Nottingham United Kingdom of Great Britain and Northern Ireland NG7 2RD IEEE Transactions on Power Electronics https://doi.org/10.1109/TPEL.2017.2730260

GaN-HEMTs suffer from trapping effects which increases device ON-state resistance RDS(on) above its theoretical value. This increase is a function of the applied DC bias when the device is in its OFF state, and the time which the device is biased for. Thus, dynamic RDS(on) of a commercial GaN-HEMT is characterised at different bias voltages in the paper by a proposed new measurement circuit. The time-constants associated with trapping and detrapping effects in the device are extracted using the proposed circuit and it is shown that variations in RDS(on) can be predicted using a series of RC circuit networks. A new methodology for integrating these RDS(on) predictions into existing GaN-HEMT models in standard SPICE simulators to improve model accuracy is then presented. Finally, device dynamic RDS(on) values of the model is compared and validated with the measurement when it switches in a power converter with different duty cycles and switching voltages. Fabrication and characterization of ultra-wide bandgap AlN based Schottky diodes on sapphire by MOCVD School of Electrical, Computer, and Energy Engineering, Arizona State University, Tempe, AZ, 85287 USA

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IEEE Journal of the Electron Devices Society https://doi.org/10.1109/JEDS.2017.2751554

AlN Schottky diodes with various device geometries were fabricated on sapphire substrate and their temperature-dependent current-voltage characteristics were analyzed. At forward bias, high ideality factors were obtained, indicating a large deviation from the ideal thermionic emission model. At reverse bias, the breakdown voltage showed a negative temperature dependence, and the leakage current was well described using a two-dimensional variable-range hopping (2D-VRH) conduction model. Furthermore, the breakdown voltages and leakage currents of the devices showed a strong dependence on the surface distance between the ohmic and Schottky contacts, but a relatively small dependence on the area of the Schottky contacts. These results suggest surface states between ohmic and Schottky contacts play a more important role than the metal/AlN interface in determining the reverse breakdown and leakage current of AlN Schottky diodes. A quantitative study of AlN Schottky diodes at high temperature reveals a geometry-dependent surface breakdown electric field and surface leakage current. Surface passivation and treatments may enhance the device performances and impact the reverse breakdown and current leakage mechanisms. These results will serve as the guidance for the design and fabrication of future AlN electronic devices. Improvement of Subthreshold Characteristic of Gate-Recessed AlGaN/GaN Transistors by Using Dual-Gate Structure State Key Discipline Laboratory of Wide Band-Gap Semiconductor Technology, School of advanced materials and nanotechnology, Xidian University, Xi’an, China State Key Discipline Laboratory of Wide Band-Gap Semiconductor Technology, School of Microelectronics, Xidian University, Xi’an, China IEEE Transactions on Electron Devices https://doi.org/10.1109/TED.2017.2741001

The subthreshold characteristic of gate-recessed high-electron-mobility transistors (HEMTs) using dual-gate (DG) architectures is systematically studied. The recessed DG structure can effectively shift the threshold voltage ( Vth ) in the positive direction. Different from the complex function expression between Vth and AlGaN thickness ( tb ) in the recessed single-gate (SG) device, the variation of Vth with tb is monotonic in the recessed DG devices.

Recessed DG device exhibits a low off-state leakage current of ∼3×10−10 A/mm and gate induced drain leakage is effectively improved. A higher ION/IOFF range of recessed DG devices broadens about 2 times and provide a wider range of tb than that of recessed SG devices. The DG structure has a stronger modulation effect on drain–source resistance ( Rds ) and gate–drain resistance ( Rgd ) than the SG devices. A lower subthreshold swing (SS) of ~100 mV/dec is obtained by recessed DG design. Due to the second gate inducing the lateral extension of depletion region between the first gate and drain, the off-state leakage and first gate reverse leakage have been significantly improved. Therefore, the recessed DG architecture design can effectively improve the fluctuation of SS and off-state current versus the different AlGaN barrier thickness. Wafer-Level Donor Uniformity Improvement by Substrate Off-Angle Control for Vertical GaN-on-GaN Power Switching Devices Engineering Department, Sciocs Co., Ltd., Hitachi, 319-1418, Japan Research Center for Micro-Nano Technology, Hosei University, Tokyo 184-0003, Japan IEEE Transactions on Semiconductor Manufacturing https://doi.org/10.1109/TSM.2017.2745504

In the mass production of GaN-on-GaN vertical power devices, the wafer-level uniformity of net donor concentration, ND-NA, of the n--drift layer in around 1015 cm-3 is an important factor because it determines the breakdown voltage. A nondestructive simple inspection is also required. In this study, we demonstrated the wafer-level nondestructive inspection of a GaN Schottky barrier diode epi-layer and improved the wafer-level net donor uniformity by controlling the off-angle of GaN substrates. Epi-structures were grown by metal-organic vapor phase epitaxy on free-standing GaN substrates with various off-angles and deviations. The variation in ND-NA was carefully analyzed using non-contact capacitance-voltage measurement and photoluminescence. Silicon and carbon concentrations were confirmed by secondary ion mass spectrometry. We found that the normalized yellow luminescence peak intensity is almost linearly related to the acceptor concentration. A carbon related variation in the acceptor concentration (NA) resulted in the non-uniformity of ND-NA, which is found to be related to the substrate off-angle of the wafer. The ND-NA uniformity can be

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improved by minimizing variation in the off-angle. Criteria of the GaN substrate off-angle deviation for power applications are discussed. First demonstration of AlSiO as gate dielectric in GaN FETs; applied to a high performance OG-FET University of California at Santa Barbara, Santa Barbara, CA 93106 USA IEEE Electron Device Letters https://doi.org/10.1109/LED.2017.2756926

Gate dielectric plays an integral role in advancing the performance and reliability of GaN based transistors. Si-alloying of aluminum oxide (Al2O3) dielectrics have been shown to provide a promising route to improve gate dielectric properties in GaN. In this work, we report on the first demonstration of a GaN FET with aluminum silicon oxide (AlSiO) as the gate dielectric. Vertical normally-off GaN MOSFETs were fabricated on bulk GaN substrate. Excellent DC performance was achieved with a breakdown voltage of 1.2 kV, an on-resistance of 2 mΩ.cm2, and a threshold voltage of 1.5 V (defined at IDS =1μA/mm). A high breakdown electric-field of 2.3 MV/cm was calculated in these devices. In addition to vertical GaN MOSFET results, a comparative study of Al2O3 and AlSiO based in-situ GaN MOS capacitors including TDDB characteristics is also presented. An E-Mode p-Channel GaN MOSHFET for a CMOS Compatible PMIC Department of Electronic and Electrical Engineering, The University of Sheffield, Sheffield, U.K. IEEE Electron Device Letters https://doi.org/10.1109/LED.2017.2747898

The operation principle of a low power E-mode p-channel GaN MOSHFET is explained via TCAD simulations. The challenges of achieving negative threshold voltage with the scaling of gate length are addressed by adjusting the mole fraction of an AlGaN cap layer beneath the gate. An inverter consisting of the proposed p-channel GaN MOSHFET with a gate length of 0.25 μm shows promise of a CMOS compatible power management IC in the megahertz range.

On the Time-Dependent Transport Mechanism Between Surface Traps and the 2DEG in AlGaN/GaN Devices Department of Engineering, Cambridge University, Cambridge CB3 0FA, U.K. IEEE Transactions on Electron Devices https://doi.org/10.1109/TED.2017.2752859

The physical mechanisms involved in the trapping and de-trapping processes associated with surface donor traps in gallium nitride (GaN) transistors are discussed in this paper. The paper challenges the conventional transient techniques adopted for extrapolating the trap energy level via experiments and TCAD simulations. Transient TCAD simulations were employed to reproduce the time-dependent electrical behavior of a metal-on-insulator field-effect transistor and explain the influence of the electric field and energy barrier on the transient time associated with the trapping and de-trapping mechanisms of surface traps. The comparison between three test structures and the relative variation of the trapping and de-trapping times with the bias and trap parameters leads to the suggestion of a proposed test structure and bias configuration to accurately extrapolate the energy level of surface traps in GaN transistors. High-power flexible AlGaN/GaN heterostructure field-effect transistors with suppression of negative differential conductance Department of Mechanical Engineering, University of Houston, Houston, Texas 77204-4006, USA Department of Printed Electronics Engineering, Sunchon National University, Suncheon-si, Jeollanam-do 57922, South Korea Department of Mechanical and Nuclear Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, USA Semiconductor Physics Research Center and Department of Semiconductor Science and Technology, Chonbuk National University, Jeonju-si, Jeollabuk-do 54896, South Korea Materials Science and Engineering Program, University of Houston, Houston, Texas 77204, USA Department of Mechanical, Aerospace, and Biomedical Engineering, The University of Tennessee, Knoxville, Tennessee 37996-2210, USA Texas Center for Superconductivity at the University of Houston (TcSUH), University of Houston, Houston, Texas 77204, USA

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Appl. Phys. Lett. http://dx.doi.org/10.1063/1.5004799

We investigate thermo-electronic behaviors of flexible AlGaN/GaN heterostructure field-effect transistors (HFETs) for high-power operation of the devices using Raman thermometry, infrared imaging, and current-voltage characteristics. A large negative differential conductance observed in HFETs on polymeric flexible substrates is confirmed to originate from the decreasing mobility of the two-dimensional electron gas channel caused by the self-heating effect. We develop high-power transistors by suppressing the negative differential conductance in the flexible HFETs using chemical lift-off and modified Ti/Au/In metal bonding processes with copper (Cu) tapes for high thermal conductivity and low thermal interfacial resistance in the flexible hybrid structures. Among different flexible HFETs, the ID of the HFETs on Cu with Ni/Au/In structures decreases only by 11.3% with increasing drain bias from the peak current to the current at VDS = 20 V, which is close to that of the HFETs on Si (9.6%), solving the problem of previous flexible AlGaN/GaN transistors. Initial leakage current paths in the vertical-type GaN-on-GaN Schottky barrier diodes International Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan Amano-Koide Collaborative Research Lab, National Institute for Materials Science, (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan Wide Bandgap Materials Group, National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan Institute of Materials and Systems for Sustainability, Nagoya University, Furo-cho c3-1, Nagoya, Aichi 464-8601, Japan Hosei University, Koganei, Tokyo 184-8584, Japan Appl. Phys. Lett. http://dx.doi.org/10.1063/1.4994627

Electrical characteristics of leakage current paths in vertical-type n-GaN Schottky barrier diodes (SBDs) on free-standing GaN substrates are investigated by using photon emission microscopy (PEM). The PEM mapping shows that the initial failure of the SBD devices at low voltages is due to the leakage current paths from polygonal pits in the GaN epilayers. It is observed that these polygonal pits originate from carbon impurity accumulation to the dislocations

with a screw-type component by microstructure analysis. For the SBD without polygonal pits, no initial failure is observed and the first leakage appeals at the edge of electrodes as a result of electric field concentration. The mechanism of leakage at pits is explained in terms of trap assisted tunneling through fitting current-voltage characteristics. Electrical analyses of GaN PIN diodes grown on patterned sapphire substrates Department of Electrical Engineering, National Tsing Hua University, Hsinchu 30013, Taiwan Journal of Vacuum Science & Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phenomena http://dx.doi.org/10.1116/1.4997900

In this article, the authors report the fabrication and characterization of quasivertical GaN p-i-n diodes with a 3 μm I-layer grown on different sizes of patterned sapphire substrates (PSSs). The diodes were characterized by current–voltage, capacitance–voltage, and deep-level transient spectroscopy. The PIN diodes grown on the smaller-size PSS showed a reverse breakdown voltage of ∼610 V and a defect concentration of 1.0 × 1016 cm−3, both of which are superior to the corresponding measurements of ∼410 V and 1.4 × 1017 cm−3 for the diodes grown on the larger-size PSS. These results indicate that the GaN PIN diodes grown on smaller-size PSS have a better quality of epitaxial layers than those grown on larger-size PSS. Determination of band offsets between p-NiO gate electrode and unintentionally doped GaN for normally-off GaN power device School of Electronics and Information Technology, Sun Yat-Sen University, Guangzhou, 510275, China State Key Laboratory of Optoelectronic Materials and Technologies, Sun Yat-sen University, Guangzhou, 510275, China Institute of Power Electronics and Control Technology, Sun Yat-Sen University, Guangzhou, 510275, China Journal of Alloys and Compounds https://doi.org/10.1016/j.jallcom.2017.09.037

Combining the p-NiO gate electrode and the stack barrier structure with unintentionally doped GaN insertion layer (serves as etching termination layer) is promising for achieving normally-off GaN power device. The band alignment and band offsets at the

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interface of NiO and GaN insertion layer play a crucial role in determining the performance of GaN device. In this letter, the p-NiO thin film/unintentionally doped GaN heterojunction was fabricated through a simple thermal oxidation method. The p-NiO thin film presents face-centered cubic crystalline structure with a band gap of approximately 3.69 eV. The interfacial band alignment of the heterojunction is characterized by X-ray photoelectron spectroscopy. Based on core-level binding energies and valence band maximum values, the valence and the conduction band offsets were determined to be 1.16 eV and 1.45 eV, respectively. The NiO/GaN heterojunction is concluded to be type-II staggered band configuration. Enhancing the Performance of AlGaN/GaN Schottky Barrier Diodes by SF6 Plasma Treatment and Deep Anode Recess Department of Electrical Engineering, National Central University, Jhongli, Taiwan ECS J. Solid State Sci. Technol. http://dx.doi.org/10.1149/2.0081711jss

In this work, low turn-on voltage (Von), low leakage current (IR) and high breakdown voltage (VBR) AlGaN/GaN Schottky barrier diodes (SBDs) are fabricated on 6-inch Silicon substrates using an anode recess process combined with SF6 plasma treatment. Using this process, turn-on voltage is reduced from 1.3 V to 0.6 V, compared to the planar untreated devices due to the reduction of Schottky barrier height by having the Schottky metal in contact with the two dimensional electron gas at the AlGaN/GaN interface. Meanwhile, the VBR is increased from 400 V to 455 V due to the presence of plasma implanted fluorine ions near the anode. This process also results in a smaller device capacitance, which leads to the reduction of reverse recovery time from 12.9∼14.4 ns to 9.6∼10.7 ns. A Lateral AlGaN/GaN Diode with MIS-Gated Hybrid Anode for Ultra-Low Turn-On and High Breakdown Voltage State Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science and Technology of China, Chengdu, 610054, People's Republic of China ECS J. Solid State Sci. Technol. http://dx.doi.org/10.1149/2.0141711jss

In this paper, we propose and experimentally demonstrate a novel lateral AlGaN/GaN diode on Si substrate. The diode features a recessed metal/Al2O3/III-nitride (MIS)-gated ohmic hybrid anode, in which the drive current can be well controlled by the MIS-Gate and flows between the two ohmic contacts from the anode to the cathode with substantially reduced overall on-resistance (Ron). With this unique architecture, the forward turn-on voltage (VT) of the diode can be flexibly trimmed, which enables a record low VT of 0.2 V obtained in the proposed diode. The incorporation of high-k dielectric in the recessed gate region and the AlGaN back barrier realize significantly leakage current (Ileakage) reduction yet high breakdown voltage (BV). The BV as high as 1100 V at Ileakage less than 1 μA/mm with drift length of 20 μm is achieved in the proposed diode. Study on Trapping Effects in AlGaN/GaN-on-Si Devices with Vertical Interconnect Structures Institute of Electronics Engineering, National Tsing Hua University, Hsinchu 300, Taiwan Department of Electrical and Computer Engineering, National University of Singapore, Singapore 119077 Department of Electronic Engineering, Chang Gung University, Tao-Yuan 333, Taiwan ECS J. Solid State Sci. Technol. http://dx.doi.org/10.1149/2.0131711jss

In this paper, AlGaN/GaN Schottky gate HEMTs on silicon based on vertical interconnect structures were fabricated and analyzed. The device with a vertical drain interconnect to the substrate shows worse current collapse based on drain lag measurement compared with both the conventional lateral device without vertical interconnect and the device with a vertical source interconnect to the substrate, implying that electrons are trapped in the epilayer due to existence of a vertical electric field. The trapped electrons in the epi and buffer layers introduce a positive shift in the threshold voltage by about 1.5 V together with an increase in the specific on-resistance, but show nearly no effect on the turn-on voltage of the Schottky junction.

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Thermal Effects between Carbon-Doped GaN and AlGaN Back-Barrier in AlGaN/GaN HEMTs on Si (111) Substrates IQE, Taunton, Massachusetts 02780, USA IQE, Bethlehem, Pennsylvania 18015, USA IQE, Greensboro, North Carolina 27409, USA ECS J. Solid State Sci. Technol. http://dx.doi.org/ 10.1149/2.0121711jss

Carbon-doped GaN and Al0.05Ga0.95N/Al0.08Ga0.92N back-barriers are employed as a semi-insulating buffer in AlGaN/GaN high- electron mobility transistor (HEMT) structures on Si (111). The AlGaN buffer exhibits improved breakdown behavior in high temperature operation owing to an additional potential barrier at the bottom of the GaN channel. The vertical and lateral leakage currents are reduced by 10X and 2X, respectively, resulting in 140 V higher reverse vertical breakdown, and 100 V higher lateral isolation breakdown voltage at 150°C. The AlGaN buffer shows slightly inferior room-temperature 2DEG transport properties as well as a roll-off in output characteristic suggesting a higher thermal impedance relative to the carbon-doped buffer. Both buffers are suitable for high-voltage operation, with the AlGaN showing advantageous leakage and breakdown properties at elevated temperature. Achieving Vertical Trench-Gate GaN MOSFETs via Process Optimization University of Maryland U.S. Naval Research Laboratory ECS Trans. http://dx.doi.org/10.1149/08007.0139ecst

Gallium nitride is a strong candidate material for advanced power electronics that exceed the capabilities of current Si and SiC technologies. The ideal device structure for GaN power switches is the vertical metal-oxide-semiconductor field effect transistor (MOSFET). Current vertical GaN MOSFETs have not reached theoretical performance limits. Optimization of these devices is required to improve their performance, particularly with respect to the dielectric/semiconductor interface along the device active regions, and processing used to fabricate the vertical channel regions. We have studied two atomic layer deposition precursor systems for ZrO2 dielectrics on both as-grown and plasma-etched c-plane GaN. Piranha etching of GaN surfaces before

ALD improved the capacitance-voltage response of the deposited ZrO2. 5-10 µm deep trenches in GaN substrates have also been fabricated, to allow more detailed study of the trench sidewalls and dielectric interfaces on the etched surfaces before and after hydroxide-based wet etching. Low-Resistance Ohmic Contacts to Al0.45Ga0.55n/ Al0.3Ga0.7n HEMTS Sandia National Laboratories ECS Meeting Abstracts http://ma.ecsdl.org/content/MA2017-02/29/1232.abstract?sid=3e7b0779-47d8-4c25-a61f-a1ae8eafe878

RF amplifiers and power electronics transistors in III-N semiconductors are increasingly important in emerging applications, as are photo-transistors for the purpose of UV light detection. Increasing the Al fraction in AlGaN-based HEMT devices enables transistors with higher breakdown voltages and a potentially favorable breakdown - specific on-resistance tradeoff. However, the advantages of higher aluminum content comes with a major challenge: Ohmic contacts with acceptable contact resistance become increasingly problematic with increasing Al content in the channel and barrier layer. We report sub 10-4 W-cm2 specific contact resistivity (rc) for a 30% channel, improving on the best prior result of approximately 2x10-4 W-cm2for AlGaN channels of at least 30% Al. A Discussion on the Latest Performance of GaN–Based Vertical Devices and the Paths Forward University of California, Davis ECS Meeting Abstracts http://ma.ecsdl.org/content/MA2017-02/29/1243.abstract?sid=3e7b0779-47d8-4c25-a61f-a1ae8eafe878

Recent progress in vertical Gallium Nitride (GaN)-based power electronic devices has been compelling. Thanks to dedicated programs like the ARPA-E SWITCHES, which led to the understanding of the challenges, while enabling several variants of vertical devices to be studied and compared. An overview of different flavors of vertical devices and their latest performance will be presented. Under the SWITCHES program, in collaboration with UCSB, NRL and Transphorm, we pursued two novel

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and practical approaches that had the common theme of markedly reducing the required device chip size compared to commercially available lateral GaN-on-Si HEMTs. CAVET [1,2] was investigated where the gated region was implemented with p-type layer on an n-channel. The study allowed us to understand the limitation of an ion-implanted current blocking layer in a 3-terminal vertical FET configuration, eliminating restrictions imposed by poor gate dielectric. In order to achieve a ‘true’ vertical transistor, OGFET, a variant of MOSFET, was developed [3,4] where, unlike the CAVET, the gating was also performed on electrons traveling perpendicular to the surface. From a CAVET, we have successfully achieved dispersion-less switching under 500ns pulses (under Pulsed I-V measurements), and over 1100V blocking in OGFET where scaling of the devices to 1A was recently achieved. While the successes of these devices speak volumes about the future possibilities and roadmap, the technical challenges are substantial. The overarching issue is related to the realization of a well-behaved buried p-n junction, which forms the basic building block of most vertical transistors for power electronics. Fundamentally, all of them require Mg based doping, and therefore the issues related to Mg activation in GaN impact everyone. Mg is a deep acceptor in GaN offering less than 1% activation under room temperature. In addition to the RT ionization related challenges, buried p-GaN activation (this strictly means the activation from hydrogen that tend to form Mg-H complexes passivating the acceptors) is a proven concern. In short, the difficulties in achieving well-behaved buried p-GaN have stunted the possibility of realizing well-behaved (buried) p-n junctions critical to vertical devices. In a MOSFET the p-layer is grown during the initial growth of the structure. This guarantees a well-behaved p-type GaN. Similar to the reports by various groups like Toyoda Gosei and HRL[5,6], Gupta et al. (UCSB) [4] showed via OGEFT that trenched vertical devices deliver promisingly high voltage results with a path towards low On-resistance (Ron). Recently Ji et al (UC Davis) [7] successfully delivered scaled devices capable of offering 1A current with 144 unit cells in parallel. Ron <4.4mΩ.cm2 was achieved in these devices, which can be lowered further with improvement in the channel mobility. Normally-off in design, the MOSFETs definitely are attractive for the

economic use of the chip area and their compatibility with presently used gate drivers A parameter to address with future research is the channel mobility to deliver lower Ron. While the typical behavior of a good gate oxide (like low trapping and small threshold voltage (Vth) shifts) also apply for these devices, the gates being designed on the sidewalls (being a or m-plane) ensure higher threshold voltages compared to c-plane HEMTs or CAVETs. This definitely alleviates the well-known tradeoff of Ron and threshold Vth to a vast degree. This talk will go over all the major achievements made over the last three years, and lay out the challenges for achieving 1.2KV switches with Ron<3mΩ.cm2 Ultra-Wide-Bandgap Aluminum Gallium Nitride Power Switching Devices Sandia National Laboratories ECS Meeting Abstracts http://ma.ecsdl.org/content/MA2017-02/31/1338.abstract?sid=3e7b0779-47d8-4c25-a61f-a1ae8eafe878

SiC- and GaN-based power semiconductor devices have in the past few years enabled great improvements in the efficiency and power density of switching power converters. A wide variety of SiC devices (e.g. MOSFETs, JFETs, BJTs, thyristors, and PiN/Schottky/JBS/MPS diodes) are now available from a number of manufacturers, and the same is true for GaN HEMTs. Thus, while vertical GaN devices are not yet mature, new research in the field is increasingly turning to the “ultra” wide-bandgap (UWBG) semiconductors, including diamond, gallium oxide, and aluminum gallium nitride (AlGaN), due to the expected scaling of the critical electric field as the bandgap to the 2.0-2.5 power. Notably, AlGaN is an alloy system, so that heterostructures are available, and it is also a polar material, which enables polarization doping. Both of these benefits significantly expand the range of device architectures that may be considered, compared to materials that do not have these properties; this is especially significant for UWBG materials, all of which have energetically deep impurity dopants that do not fully ionize at room temperature. This talk will report on both vertical PiN diodes and lateral HEMTs composed of Al-rich AlxGa1-xN (x ≥ 0.7, EG ≥ 5.2 eV) designed as prototype power switching devices.

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New Approaches for Shrinking the Performance Gap for GaN Power Devices Rensselaer Polytechnic Institute University of South Carolina ECS Trans. http://dx.doi.org/10.1149/08007.0147ecst

The expected performance of GaN and SiC based power devices far exceeds that of Si power transistors, but the gap between the expected and achieved performance is much larger for GaN transistors. In this paper, we discuss new approaches for shrinking the performance gap for GaN power devices. They include using the quantum well channel designs that lead to the electron wave function penetration into wide band gap cladding layers with the commensurate increase in the breakdown voltage while keeping the advantage of a high mobility in the device channel. The gate edge engineering (beyond just using field plates) optimizes the voltage distribution in the drain-to-gate spacing. It could be combined with a low conducting passivation for smoothing or even eliminating the sharp maximum of the electric field in the vicinity of the gate and field plate edges. Additional contacts in the drain-to-gate spacing for the field control and variable doping implants should allow for further optimization. The perforated channel designs could alleviate both the parasitic series resistance problem and the heat dissipation problem. Extending the gate perforations into the drain-to-gate region allows for a considerable reduction of the switching RC constant with a commensurate decrease in power dissipation. The ultimate design could use the lateral-vertical structures. The AlInN/AlN/GaN technology is uniquely poised for the breakthrough in high temperature performance. We predict that the combination of these approaches will dramatically shrink the performance gap firmly establishing GaN as a superb material for power applications. High Voltage GaN Lateral Photoconductive Semiconductor Switches U.S. Naval Research Laboratory, Washington, DC, 20375, USA Sotera Defense Solutions, Herndon, Virginia 20171, USA George Mason University, Fairfax, Virginia 22030, USA ECS J. Solid State Sci. Technol. http://dx.doi.org/10.1149/2.0231711jss

High voltage (>4000 V) GaN lateral photoconductive semiconductor switches (PCSSs) were developed and characterized. The epitaxial structure consisted of 1.4 μm of semi-insulating GaN grown on a SiC substrate. Intrinsic mode operation, where above bandgap light is used to trigger the PCSS, results in the highest amount of photocurrent. These PCSSs can also be triggered in extrinsic mode, where sub-bandgap illumination excites carriers from extrinsic defect levels, but this results in a significantly lower photocurrent. Triggering at near bandgap with 10 V applied, the on-state photocurrent is over eight magnitudes higher than the dark off-state leakage, indicating extremely high responsivity. A 293 nm picosecond pulse width laser was used to determine the rise time of the PCSS to be ∼160 ps. Various geometry devices were fabricated, and the low voltage on-state current obeyed a linear trend as a function of perimeter/gap optically while optically gating the PCSS, which is analogous to the width/length of a metal oxide semiconductor field effect transistor. Off-state breakdown voltages >4000 V were achieved and were likely limited by the thickness of the GaN epitaxial layer. Simulation Study of High Voltage Vertical GaN Nanowire Field Effect Transistors Illinois Institute of Technology Tyndall National Institute Queen’s University ECS Trans. http://dx.doi.org/10.1149/08007.0069ecst

Concept of vertical Gallium Nitride (GaN) nanowire field effect transistors (NWFETs) for high voltage power electronic applications is investigated through three dimensional (3D) TCAD simulations in this paper. The proposed GaN NWFET can operate either in a normally-off or a normally-on mode depending on the specific device design. A gate-all-around (GAA) structure coupled with a strong dielectric REduced SURface Field (RESURF) effect has the potential to offer blocking voltages over 900 V with very low specific on-resistance for the NWFETs. VRB2/RON and QGDx RDS(ON) Figures of Merits (FoMs) of the NWFET are extracted and compared with other state of the art GaN, SiC and Si field effect transistors to get a comparative understanding of the potential of the NW architecture for high voltage applications.

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Novel Implantation Processing and Characterization for Scalable GaN Power Devices University of California, Los Angeles, UCLA U.S. Naval Research Laboratory ECS Trans. http://dx.doi.org/10.1149/08007.0251ecst

Novel ion implantation processing enables p-type doping for high performance vertical GaN p-n power devices. Multicycle Rapid Thermal Annealing with an N2 ambient at 200 psi, pulsed annealing up to ~1400 °C, and an appropriate dielectric encapsulant, is utilized to improve activation efficiency and, ultimately, p-n junction performance through selective ion implantation and processing optimization. Here, the focus is on analysis of MRTA activated, Mg+ implantation into GaN deposited on sapphire substrates. The link between defects and implant activation will be assessed through the use of novel structural materials characterization techniques. X-ray based reciprocal space mapping as a function of the implant and subsequent annealing will be shown to correlate strain and defect formation with dopant activation. Electron microscopy defect analysis is demonstrated to provide localized strain measurements after annealing. Understanding the evolution of implant-induced point defect concentrations and dislocation formation, will lead to effective p-type dopant activation and high device performance. 650 Volt GaN Commercialization Reaches Automotive Standards Transphorm Inc. Transphorm Japan ECS Trans. http://dx.doi.org/10.1149/08007.0017ecst

With its proven ability to reduce size (form factor) and save energy (high efficiency) Gallium Nitride (GaN) is now no longer a nice to have, it is a must-have for power conversion. High voltage (HV) GaN HEMTs (also called GaN FETs) in the range of 650 to 900 volts are becoming the next standard for power conversion. GaN provides cost-competitive, easy-to-embed solutions that reduce energy loss by >50 percent, shrink system sizes by >40 percent, to simplify power converter/inverter design and manufacturing. These benefits are being realized today in various markets: Consumer, Industrial, Server, Servo Motors and Drives, Solar,

Telecommunications, and recently Hybrid and Electric Vehicles. Having successfully completed JEDEC qualification and commercialization of HV-GaN, we will now review the first ever Automotive (AEC Q101) Qualification for GaN and discuss in detail results for highly stressed robustness tests, FIT rates & lifetime testing. Recent Progress in SiC and GaN Power Devices Zhejiang University ECS Trans. http://dx.doi.org/10.1149/08007.0037ecst

Wide bandgap SiC and GaN power devices are attractive for next-generation power electronic systems with increased efficiency and power density. In this paper, we review recent progress in SiC and GaN power devices, including the following. (1) Interface optimization techniques for SiC MOSFETs (e.g. NO/N2O annealing, P incorporation, metal interfacial-layer, high-k dielectric deposition, etc.) will be discussed. (2) Long-term reliability of SiC MOSFETs with special focus on time-dependent dielectric breakdown (TDDB) will be presented. (3) We will introduce our latest progress in the development of superjunction SiC devices, which can break the fundamental limit of the conventional unipolar devices. (4) In GaN-based lateral power devices, the 2DEG channel is an inherent normally-on channel. To achieve fail-safe operation and simpler gate drive circuit, normally-off device techniques will be introduced and compared. Current and Future Directions in Power Electronic Devices and Circuits Based on Wide Band-Gap Semiconductors Advanced Research Projects Agency-Energy Advanced Research Project Agency-Energy Booz Allen Hamilton ECS Meeting Abstracts http://ma.ecsdl.org/content/MA2017-02/29/1237.abstract?sid=5232db56-5ce0-489c-934d-730e54ca610f

Electricity generation currently accounts for 40% of primary energy consumption in the U.S., and over the next 25 years is projected to increase more than 50% worldwide. Electricity continues to be the fastest growing form of end-use energy. Power electronics are responsible for controlling and converting electrical power to provide optimal conditions for

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transmission, distribution, and load-side consumption. Estimates suggest that the fraction of electricity processed through power electronics could be as high as 80% in the US by 2030 (including generation and consumption), approximately a twofold increase over the current proportion. Development of advanced power electronics with exceptional efficiency, reliability, functionality, and form factor will provide the U.S. with a competitive advantage in deployment of advanced energy technologies. Additionally, widespread integration of innovative converters offers substantial energy saving opportunities both directly, by inherently more efficient designs, and indirectly, by facilitating higher levels of adoption for fundamentally higher performing materials. High impact opportunities exist across a variety of applications, including power supplies, motor drives, automotive (including DC fast charging infrastructure), data centers, and aerospace, as well as grid and distributed energy resources (wind, solar PV, MV/HVDC, FACTS). Fast switching power semiconductor devices are the key to increasing the efficiency and reducing the size of power electronic systems. For the last three decades, silicon power devices (MOSFETS, IGBTs, and diodes) have dominated the power device market. During this time there have been tremendous improvements in silicon power device performance. However, these devices are now approaching the physical limits of silicon. Alternative wide-band gap semiconductor materials, such as silicon carbide (SiC) and gallium nitride (GaN) are enabling a new generation of power devices that will far exceed the performance of silicon-based devices. Wide band-gap semiconductors enable continued improvement of the efficiency and reduced system size of power electronics. In this presentation, future directions in emerging wide bandgap semiconductor devices will be discussed. Furthermore, we will discuss the development and deployment of a new class of efficient, lightweight, and reliable power converters through transformational advances in circuit topologies, advanced control and drive electronics, and innovative packaging. Vertical GaN Devices Enabled By Selective Area P-Type Doping Naval Research Laboratory George Mason University U.S. Naval Research Laboratory University of California, Los Angeles

ECS Meeting Abstracts http://ma.ecsdl.org/content/MA2017-02/29/1245.abstract?sid=5232db56-5ce0-489c-934d-730e54ca610f

A key element for enabling high performance vertical GaN power electronic devices is the capability to realize selective area p-type doping. The ability to arbitrarily define p-type regions through ion implantation eliminates the need for epitaxial regrowth on etched surfaces, which is currently a well-known technological roadblock. However, activation of implanted Mg is also a challenge, since activation of the Mg acceptors requires annealing at temperatures above the thermodynamic stability limits of GaN in atmosphere. Implementing the symmetric multi cycle rapid thermal annealing (SMTRA) technique has been shown to activate up to ~10% of the implanted Mg dopant atoms. This technique includes a temporary thermally stable capping layer, annealing in a nitrogen overpressure, and performing a well-optimized annealing temperature profile including multiple spike anneals. Vertical GaN junction barrier Schottky (JBS) diodes and Schottky barrier diodes (SBDs) with implanted junction termination extension (JTE) are demonstrated using the SMRTA process, as are process module development toward trench MOSFET devices. High-voltage MIS-gated GaN transistors Research Institute of Electrical Communication SystemsTomsk State University of Control Systems and RadioelectronicsTomskRussia Research-and-Production Company “Micran”TomskRussia Physical–Technical InstituteNational Research Tomsk Polytechnic UniversityTomskRussia Semiconductors https://doi.org/10.1134/S106378261709010X

Transistors with a high electron mobility based on AlGaN/GaN epitaxial heterostructures are promising component types for creating high-power electronic devices of the next generation. This is due both to a high charge-carrier mobility in the transistor channel and a high electric durability of the material making it possible to achieve high breakdown voltages. For use in power switching devices, normally off GaN transistors operating in the enrichment mode are required. To create normally off GaN transistors, the subgate region on the basis of p-GaN doped with magnesium is more often used. However,

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optimization of the p-GaN epitaxial-layer thickness and doping level makes it possible to achieve a threshold voltage close to Vth = +2 V for the on-mode of GaN transistors. In this study, it is shown that the use of a subgate MIS (metal–insulator–semiconductor) structure involved in p-GaN transistors results in an increase in the threshold voltage for the on-mode to Vth = +6.8 V, which depends on the subgate-insulator thickness in a wide range. In addition, it is established that the use of the MIS structure results in a decrease in the initial transistor current and the gate current in the on mode, which enables us to decrease the energy losses when controlling powerful GaN transistors. A GaN enhancement-mode reverse blocking MISHEMT with MIS field-effect drain for bidirectional switch State Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science and Technology of China (UESTC), Chengdu, China Institute of Electronic and Information Engineering of UESTC in Guangdong, Dongguan, China Journal of Computational Electronics https://doi.org/10.1007/s10825-017-1079-3

In this work, a novel GaN-based reverse blocking metal–insulator–semiconductor high electron mobility transistor (RB-MISHEMT) with enhancement mode (E-mode) is investigated by the TCAD simulation. To enable the device with capability of blocking reverse current, a MIS field-effect drain consisting of electrically shorted ohmic and recessed MIS structure is adopted. The proposed GaN E-mode RB-MISHEMT features a low reverse current of 10 μμ A at − 900 V and a low turn-on voltage of drain electrode of 0.38 V at 10 mA. On-state power loss of the bidirectional switch based on proposed GaN E-mode RB-MISHEMT shows a 34% reduction compared with that of the bidirectional switch based on GaN E-mode reverse conducting MISHEMT. And the proposed E-mode RB-MISHEMT is also compatible with standard E-mode MISHEMT. The high performance and processing compatibility of the proposed GaN RB-MISHEMT show that the device is promising for future power applications.

Normally-off fully recess-gated GaN metal–insulator–semiconductor field-effect transistor using Al2O3/Si3N4 bilayer as gate dielectrics Institute of Microelectronics, Peking University, Beijing 1000871, China Microsystem and Terahertz Research Center, China Academy of Engineering Physics, Chengdu 610200, China Applied Physics Express https://doi.org/10.7567/APEX.10.106502

By a self-terminating gate recess etching technique, a normally-off fully recess-gated GaN metal–insulator–semiconductor field-effect transistor (MISFET) was fabricated using Al2O3/Si3N4 bilayer as gate dielectrics. Owing to the high breakdown electric field (~10 MV/cm) of the gate dielectrics, the device exhibits a large gate swing of 18 V, a high threshold voltage of 1.7 V (at I D = 100 µA/mm), a large maximum drain current of 534 mA/mm, a gate leakage current lower than 20 nA/mm in the whole gate swing, and a high OFF-state breakdown voltage of 1282 V. Furthermore, owing to the high gate overdrive (V GS − V TH), the on-resistance of the device only increases by 5.4% under a constant stress of V GS/V DS = 18 V/1 V. Analytical derivation of interface state density from sub-threshold swing in AlGaN/GaN metal–insulator–semiconductor high-electron-mobility transistors Graduate School of Engineering, University of Fukui, Fukui 910-8507, Japan Japanese Journal of Applied Physics https://doi.org/10.7567/JJAP.56.104101

We present an analytical expression of sub-threshold swing (SS) in AlGaN/GaN metal–insulator–semiconductor high-electron-mobility transistors (MIS-HEMTs), and describe dependences of SS on structural and relevant material parameters of the MIS-HEMTs. In this work, we derived two different equations where interface states reside at the dielectric/AlGaN interface (proposed equation) and at the AlGaN/GaN interface (conventional equation), which is the customary assumption in the literature. Analysis indicates that SS calculated by using conventional equation is always higher than that calculated by using proposed equation. To confirm the validity of the proposed equation, AlGaN/GaN MIS-HEMTs with and without recess etched gate structure are fabricated and their corresponding interface state densities are derived directly from the

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measured SS. The MIS-HEMTs with recess show higher SS than those without recess, which is attributed to the increase of interface state density, probably due to the damage introduced during the etching process. Current linearity and operation stability in Al2O3-gate AlGaN/GaN MOS high electron mobility transistors Graduate School of Information and Science Technology and Research Center for Integrated Quantum Electronics (RCIQE), Hokkaido University, Sapporo 060-8628, Japan Fujitsu Laboratories Ltd., Atsugi, Kanagawa 243-0197, Japan Japanese Journal of Applied Physics https://doi.org/10.7567/JJAP.56.101001

To investigate current linearity and operation stability of metal–oxide–semiconductor (MOS) AlGaN/GaN high electron mobility transistors (HEMTs), we have fabricated and characterized the Al2O3-gate MOS-HEMTs without and with a bias annealing in air at 300 °C. Compared with the as-fabricated (unannealed) MOS HEMTs, the bias-annealed devices showed improved linearity of I D–V G curves even in the forward bias regime, resulting in increased maximum drain current. Lower subthreshold slope was also observed after bias annealing. From the precise capacitance–voltage analysis on a MOS diode fabricated on the AlGaN/GaN heterostructure, it was found that the bias annealing effectively reduced the state density at the Al2O3/AlGaN interface. This led to efficient modulation of the AlGaN surface potential close to the conduction band edge, resulting in good gate control of two-dimensional electron gas density even at forward bias. In addition, the bias-annealed MOS HEMT showed small threshold voltage shift after applying forward bias stress and stable operation even at high temperatures. Improved reverse recovery characteristics of inAlN/GaN schottky barrier diode using a SOI substrate Department of Electronics Engineering, Chang Gung University, Tao-Yuan 33302, Taiwan Departments of Radiation Oncology, Chang Gung Memorial Hospital, LinKou, Taiwan, R.O.C The college of engineering, Ming Chi University of Technology, Taishan, Taiwan, R.O.C Department of Electrical Engineering, National Central University, Taoyuan 32001, Taiwan

Semiconductor Science and Technology https://doi.org/10.1088/1361-6641/aa8261

The low-frequency noise (LFN) and reverse recovery charge characteristics of a six-inch InAlN/AlN/GaN Schottky barrier diode (SBD) on the Si-on-insulator (SOI) substrate were demonstrated and investigated for the first time. Raman spectroscopy indicated that using SOI wafers lowered epitaxial stress. According to the DC and LFN measurements at temperatures ranging from 300 to 450 K, the InAlN/GaN SBD on the SOI substrate showed improved forward and reverse currents and achieved a lower reverse recovery charge, compared with a conventional device.

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GROUP 4 - Advanced Electronics and RF Group leader: Jean-Claude Dejaeger (IEMN)

Information selected by Jean-Claude Dejaeger (IEMN) and Yvon Cordier (CRHEA-CNRS)

Demonstration of GaN Static Induction Transistor (SIT) Using Self-Aligned Process School of Electrical and Computer Engineering, University of California, Davis, CA 95616 USA IEEE Journal of the Electron Devices Society https://doi.org/10.1109/JEDS.2017.2751065

The rapid development of RF power electronics requires amplifier operating at high frequency with high output power. GaN-based HEMTs as RF devices have made continuous progress in the last two decades showing great potential for working up to G band range. However, vertical structure is preferred to obtain higher output power. In this paper, we have designed and fabricated GaN Static Induction Transistor (SIT) using the self-aligned technology, which was accomplished mainly by using a SiO₂ lift-off step in buffered oxide etch (BOE). By optimizing the time in ultrasonic bath and in BOE, the SiO₂ and the metal on top were removed completely which resulted in the gate metal only on the sidewalls. Both dry and wet etch techniques were investigated to reduce the gate leakage on the etched surface. The low power dry etch combined with the tetramethylammonium hydroxide (TMAH) wet etch can effectively reduce the etch damages, decrease the gate leakage and enhance the gate control over the channel. Reliability Characteristics and Mechanisms of HRL’s T3 GaN Technology HRL Laboratories, LLC at 3011 Malibu Canyon Rd., Malibu, California, 90265, USA IEEE Transactions on Semiconductor Manufacturing https://doi.org/10.1109/TSM.2017.2748921

HRL’s T3 GaN MMIC technology is evaluated using DC reliability experiments, including a voltage step-stress test, a temperature step-stress test, and a 3-temperature life test. The drain voltage step-stress test revealed three distinct regions of operation through gate leakage characteristic changes: burn-in stabilization up to 5 V, followed by stable operation up to 20 V, then voltage-dependent degradation up to catastrophic failure around 30 V. As a result, a de-rated recommended safe-operating limit of Vds = 12V

was established. The temperature step-stress test resulted in clear Arrhenius temperature-dependent degradation of the device on-resistance above 250 °C. Similarly, a recommended safe-operating limit of 150 °C was established for the technology. Finally, the 3-temperature life test resulted in clear temperature group separation and an activation energy of 2.52 eV, with a mean time-to-failure of 4 million hours at 150 °C with only a +0.2 ohm.mm increase in device on-resistance. Physical failure analysis of degraded parts showed the mechanism was a defect formation in the epitaxial barrier layer at the drain edge of the gate. Finite-element electrical simulations duplicated this degradation mechanism by modeling the defect as a void, which depleted the 2DEG and therefore increased device on-resistance. Self-Aligned AlGaN/GaN FinFETs HRL Laboratories LLC, Malibu CA 90265 USA IEEE Electron Device Letters https://doi.org/10.1109/LED.2017.2747843

We have demonstrated highly-scaled, self-aligned AlGaN/GaN FinFETs which were fabricated using e-beam lithography and a regrown n+ GaN ohmic process with a sacrificial dummy gate. Our devices were very aggressively scaled, with fin widths, gate length, and source drain spacing as small as 50 nm, 60 nm, and 200 nm respectively. DC characteristics, when normalized to active device periphery (number of fins times fin width), showed peak transconductance of 1.5 mS/μm and on resistance of 390 ohm-μm. Enhancement mode device operation was observed for fin widths below 100 nm. Highly efficient wideband X-band MMIC class-F power amplifier with cascode FP GaN HEMT HRL Laboratories, LLC, USA Electronics Letters https://doi.org/10.1049/el.2017.1672

Wideband high-power single-chip X-band class-F power amplifier with excellent output performances is reported. In order to achieve high-power class-F operation under minimised output capacitance

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impact at the frequency, high-voltage operation with minimised device size is pursued and its voltage swing becomes maximised by adopting high breakdown field-plate (FP) GaN high-electron-mobility transistor (HEMT) devices with cascode configuration. For the fabrication, 0.14 μm FP AlGaN/GaN HEMT technology with 58 GHz fT and ~100 V breakdown is used. Based on on-wafer test at 44 V Vdd, the fabricated class-F power amplifier delivers maximum 61.1% power added efficiency (PAE) with 9.2 W at 10.2 GHz. With the help of high-voltage operating cascode devices of minimised size, it also delivers excellent bandwidth of 1.6 GHz at the point of 50% PAE and high-power density of 4.42 W/mm is demonstrated. Design of Multioctave Bandwidth Power Amplifier Based on Resistive Second-Harmonic Impedance Continuous Class-F Beijing University of Posts and Telecommunications, Beijing, China IEEE Microwave and Wireless Components Letters https://doi.org/10.1109/LMWC.2017.2734764

In this letter, a generic method is presented for multioctave power amplifier (PA) based on extended version of the continuous class-F. The theory allows resistive second-harmonic impedance and sacrifices part of efficiency to get a bandwidth over one octave. A high-voltage GaN HEMT is adopted to achieve high output power and drain efficiency. Finally, a 0.2–2.5 GHz miniature multioctave PA is designed and fabricated. Experimental results show the drain efficiency of 55.5%–70.3% and the output power of 43.7–46.9 dBm across 0.2–2.5 GHz (170%). The compact size of the proposed PA can also be observed with only 2.6 cm ×5.5 cm, which is greatly reduced compared with other PAs with similar performances. Design of inverse Class-F power amplifier based on dual transmission line with 87.4% drain efficiency School of Electronic Engineering, Beijing Key Laboratory of Work Safety Intelligent Monitoring, Beijing University of Posts and Telecommunications, 100876, Beijing, China Microwave and Optical Technology Letters http://dx.doi.org/10.1002/mop.30859

In this paper, an inverse Class-F power amplifier (PA) based on dual transmission line (DTL) is presented. The output matching network (OMN) with DTL has a

simple and compact circuit topology compared with other harmonic-tuned OMNs with open/short shunt stubs and provides up to 6th harmonic suppression. In addition, the DTL structure is equivalent to a quarter wavelength transformer for fundamental matching. A GaN HEMT is adopted to achieve high output power and high drain efficiency in the proposed inverse Class-F PA. Finally, a 2.4 GHz inverse Class-F PA is designed and fabricated. The experimental results show the highest drain efficiency of 87.4% in the operating frequency with the corresponding output power of 44.5 dBm, and adjacent channel power ratio (ACPR) of −50.8/-51.6 dBc with digital predistortion technique (DPD) at 2.4 GHz. A New Small-Signal Parameter Extraction Technique for Large Gate-Periphery GaN HEMTs Nanolab, Department of Electrical Engineering, IIT Kanpur, Kanpur 208016, India Department of Science and Engineering, Macquarie University, Sydney, NSW 2109, Australia IEEE Microwave and Wireless Components Letters https://doi.org/10.1109/LMWC.2017.2746661

In this letter, we propose a method to extract the small-signal equivalent circuit model for GaN HEMTs using extrinsic-level RF broadband (0.5-50 GHz) Z-parameters. The measured Z-parameters of large gate-periphery GaN devices exhibit certain interesting characteristics, due to their inherently larger intrinsic capacitances and their subsequent interaction with the extrinsic inductances. We exploit these characteristics to simultaneously extract the intrinsic as well as the extrinsic small-signal model components and successfully validate it with measured S-parameter data for a 10 x 90 μm GaN device. Optimal Definition of Class F for Realistic Transistor Models Department of Electrical and Computer Engineering, The Ohio State University, Columbus, OH 43210 USA Department of Electronic Engineering, National University of Mexico, Mexico City 04510, Mexico IEEE Transactions on Microwave Theory and Techniques https://doi.org/10.1109/TMTT.2017.2743714

An optimal three-harmonic definition of class F at the intrinsic level is presented for realistic transistor models exhibiting IV characteristics with a nonzero

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knee voltage. This updated class-F definition is needed for use with the recently reported embedding device model, which predicts in a single harmonic balance simulation the voltage and current waveforms required at the package reference planes to sustain an intrinsic mode of operation. Optimal class-F operation is obtained by setting to infinite the third-harmonic output impedance of the transistor IV characteristics instead of using an open load for the third-harmonic termination. This is achieved by fine tuning the class-F quasi-rectangular drain voltage waveform. The required third-harmonic component of the drain voltage in the optimal class F is then found to be generated by the lossless inductive termination of the third-harmonic component of the drain displacement current arising from the nonlinear drain-to-source capacitance. The proposed class-F definition is verified for a gallium nitride (GaN) high electron mobility transistor using third-harmonic load-pull simulations with a realistic GaN transistor model. The optimal third-harmonic load termination predicted using the class-F definition is found to be in full agreement with the one obtained from the drain efficiency contour plots. A close agreement is also obtained for the predicted and measured optimal third-harmonic load termination, bringing experimental support for the proposed class-F definition. Accurate Modeling of GaN HEMT RF Behavior Using an Effective Trapping Potential GigaHertz Centre, Microwave Electronics Laboratory, Department of Microtechnology and Nanoscience, Chalmers University of Technology, SE-412 96 Göteborg, Sweden IEEE Transactions on Microwave Theory and Techniques https://doi.org/10.1109/TMTT.2017.2748950

This paper investigates the back-gating effects due to traps, and presents a new nonlinear trap modeling approach suitable for gallium nitride (GaN) high electron mobility transistors (HEMTs). It is shown that the traps have nonidentical influence on the channel compared with the gate. The potential due to trapped electrons in the buffer and the gate-source voltage need to be differentiated to model their respective influence on conductivity of the 2-D electron gas. Hence, the back-gating potential due to traps cannot be included in the transistor model by directly offsetting the gate-source voltage. A new modulation factor is therefore introduced to create

an effective back-gating potential, and thereby improve the modeling of trapping effects. The proposed nonlinear trap model is shown to accurately predict the trapping behavior for a large voltage operating region. A detailed procedure is presented to derive the model parameters from basic device measurements. The model is experimentally validated and shown to accurately predict dc-, pulsed-IV, and large-signal waveform performance for a commercial GaN HEMT. Linearity Enhancement of a Fully Integrated 6-GHz GaN Power Amplifier Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA 02139 USA School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore Department of Computer Science, National University of Singapore, Singapore IEEE Microwave and Wireless Components Letters https://doi.org/10.1109/LMWC.2017.2746673

A large-signal nonlinearity compensation technique is developed to improve the linearity of RF GaN power amplifiers. The design of a high power amplifier employing both common-source (CS) and common-gate (CG) GaN high-electron mobility transistors is presented for the IEEE 802.11p standard. The power amplifier is fabricated in 0.25-μm GaN-on-SiC technology and occupies 1.7 mm x 1.2 mm. The measurements show that 35-dBm output 1-dB compression point (OP1 dB) is obtained with 39-dBm OIP3 for two-tone intermodulation distortion testing. It also achieves 31% drain efficiency at 28.8-dBm output power with 10-V supply voltage considering a more than 6-dB back-off for orthogonal frequency division multiplexing-modulated signals. Linearity enhancement by means of the proposed CS-CG configuration is demonstrated in a fully integrated GaN power amplifier at 6 GHz. Heterogeneous Integration of Microwave GaN Power Amplifiers with Si Matching Circuits Fujitsu Laboratories Ltd., 10-1 Morinosato-Wakamiya, Atsugi 243-0197, Japan IEEE Transactions on Semiconductor Manufacturing https://doi.org/10.1109/TSM.2017.2756823

GaN high electron mobility transistors (HEMTs) were integrated into monolithic microwave integrated

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circuits (MMICs) by molding hetero-substrates and using a redistribution layer (RDL). Driver amplifiers (DAs) and high-power amplifiers (HPAs) on SiC substrates were molded with matching circuits on Si substrates including Cu-filled through-substrate vias (TSVs), and their circuits on hetero-substrates were connected using a Cu RDL. This was the first attempt to fabricate hetero-substrate MMICs with five chips for two-stage power amplifiers. This method will be very useful to increase the achievable quantity of small DAs and HPAs—as opposed to using large MMICs with matching circuits on a SiC substrate—and to reduce production costs. Furthermore, various frequency bands, such as the millimeter-wave band, can be accommodated by changing the Si chips of the matching circuits. Design of Multioctave High-Efficiency Power Amplifiers Using Stochastic Reduced Order Models Department of Electrical Engineering and Electronics, University of Liverpool, Liverpool, L69 3GJ, U.K IEEE Transactions on Microwave Theory and Techniques https://doi.org/10.1109/TMTT.2017.2750164

This paper presents a novel general design method of frequency varying impedance matching. The method is applied to design of a broadband high-efficiency power amplifier (PA). The proposed method defines the optimal impedance regions of a PA at several frequency sections over the operational frequency band. These regions contain the impedances that can achieve a high output power and a high-power added efficiency (PAE) simultaneously. A low-pass LC-ladder circuit is selected as the matching network (MN). The element values of the MN can be obtained using a synthesizing method based on stochastic reduced order models and Voronoi partition. The MN provides desired impedance in the predefined optimal impedance region at each frequency section. Thus, optimal output power and PAE of the PA can be achieved. To validate the proposed method, two eighth-order low-pass LC-ladder networks are designed as the input and output MNs, respectively. A gallium nitride (GaN) HEMT from Cree is employed as the active device. Packaging parasitic of the transistor has been taken into account. A PA is designed, fabricated, and measured. The measurement results show that the PA can achieve P1 dB PAE of better than 60% over a fractional bandwidth of 160% (0.2-1.8 GHz). The output power is 42-45 dBm (16-32 W), and the gain is 12-15 dB. The

performance of the PA outperforms existing broadband high-efficiency PAs in many aspects, which demonstrates the excellence of the proposed method. Overview of the assembly and packaging of wide band gap semiconductor technologies Beijing Microelectronic Technology Institute (BMTI), China Aerospace Science Corporation (CASC), China Electronic Packaging Technology (ICEPT), 2017 18th International Conference on https://doi.org/10.1109/ICEPT.2017.8046661

This paper summarizes the development of the third-generation semiconductors, which are also named Wide - Band-Gap(WBG) semiconductor, typified by SiC, GaN. Since the power devices based on the WBG semiconductor should be operated on harsh environments with high temperature and high frequency, the assembly and packaging should also withstand such environment. The technology of die-attachment and interconnection technologies suitable for these power devices are presented in this paper. Through the comparison of several advanced corporations' power devices, prudent technology to achieve a full comprehension in this market. The focus discussion is the roadmap of package technologies in the power devices based on the WBG semiconductors. And finally, further anticipation for future developments of the package technology in such applications is given. DC and RF Performance of AlGaN/GaN/SiC MOSHEMTs With Deep Sub-Micron T-Gates and Atomic Layer Epitaxy MgCaO as Gate Dielectric School of Electrical and Computer Engineering and Birck Nanotechnology Center, Purdue University, West Lafayette, IN, USA Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA, USA Air Force Research Laboratory, Sensors Directorate, Wright-Patterson Air Force Base, Dayton, OH, USA IEEE Electron Device Letters https://doi.org/10.1109/LED.2017.2746338

In this letter, we report on the dc and RF performance of AlGaN/GaN metal-oxide-semiconductor high-electron mobility transistors (MOSHEMTs) with various gate lengths ( LG ) from 90 to 500 nm using atomic-layer-epitaxy single crystalline Mg0.25Ca0.75O as gate dielectric. The 90-

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nm T-gate MOSHEMT simultaneously demonstrates a ft/fmax of 113/160 GHz with high on/off ratio of 5×108 . The on/off ratio increases to 2×1011 at LG=350 nm by reducing short channel effects. The gate leakage current is around 10−11 A/mm at off-state and 10−5 A/mm at on-state. A 160 nm LG MOSHEMT also exhibits an output power density of 4.18 W/mm at f=35 GHz and VDS=20 V. MgCaO demonstrates to be a promising dielectric for GaN MOS technology in serving as the surface passivation layer and reducing the gate leakage current while maintaining high RF performances for high-power applications. C-band energy harvester by Si RFICs with GaN diodes for microwave power transfer The Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Chuo, Sagamihara, Kanagawa 252-5210, Japan School of Physical Science, Space and Astronautical Science, The Graduate University for Advanced Studies Department of Engineering and Applied Sciences, Sophia University Research Field in Engineering, Research and Education Assembly, Kagoshima University, 1-21-40 Korimoto Kagoshima 890-0065 Japan UM-Services, Higashi-gotannda, Shinagawa, Tokyo 141-0022 Japan Radio-Frequency Integration Technology (RFIT), 2017 IEEE International Symposium on https://doi.org/10.1109/RFIT.2017.8048231

A compact C-band energy harvester is designed, test fabricated, and measured. An RF hybrid semiconductor integrated circuit (RF-HySIC) rectifier was fabricated by comprising a Si RFIC matching circuit and a GaN diode. The energy harvester at 5.8-GHz was made in a multi-circuit fashion under a wide input power range and input power control by field-effect transistor switch. The maximum RF-DC conversion efficiencies from a proto type of RF-HySIC rectifier with 50% and 13% were achieved at 5.1 and 5.8 GHz, respectively. Multi-octave linear efficient GaN power amplifier HRL Laboratories, LLC, 3011 Malibu Canyon Rd. Malibu, CA 90265 Radio-Frequency Integration Technology (RFIT), 2017 IEEE International Symposium on https://doi.org/10.1109/RFIT.2017.8048242

GaN RF technology has continued to demonstrate state-of-the-art power, efficiency, linearity, and low-noise performance in RF and mm-wave band. Here, we report on a multi-octave (100 MHz–8 GHz), linear nonuniform distributed amplifier (NDPA) in a MMIC architecture using scaled 120-nm short-gate-length GaN HEMTs. The linear NDPAs were built with six sections in a nonuniform distributed amplifier approach, where each cell consists of main and gm3 cells. The small signal gain was >10 dB over the band, with saturated CW output power of ∼35 dBm at Vdd = 17 V. The PAE improved by 7%–10% within the band compared to the previous NDPA with 150-nm gate-length GaN FETs. Based on two-tone testing, the linear NDPA showed improved OIP3 of ∼50 dBm, compared to OIP3 of 42 dBm for the NDPA without linearization. Under QPSK LTE waveform, the ACPR was improved by ∼10 dBc at average output power of 23 dBm, without digital pre-distortion. A Design Strategy for Bandwidth Enhancement in Three-Stage Doherty Power Amplifier With Extended Dynamic Range Centre for Applied Research in Electronics, IIT Delhi, Delhi 110016, India Indian Institute of Technology Delhi, Delhi 110016, India Department of Electronics and Communication Engineering, Indian Institute of Technology Roorkee, Roorkee 247667, India IEEE Transactions on Microwave Theory and Techniques https://doi.org/10.1109/TMTT.2017.2751044

This paper presents a design strategy to enhance the bandwidth of three-stage Doherty power amplifier (DPA) with operation upto 12-dB back-off. Based on the proposed strategy, a broadband 48-W DPA is designed and implemented using packaged CREE GaN transistors. The measured drain efficiency of 50%-61.8% at 12-dB back-off and 51.9%-66.2% at 6-dB back-off is obtained over the frequency range of 600-900 MHz. Over this 300-MHz band, the drain efficiency is between 51.1% and 78% at saturation. This corresponds to 40% fractional bandwidth. The three-stage DPA is also linearized with a three carrier 15-MHz WCDMA signal with a PAPR of 10.6 dB at various frequencies within operating band and shows the output signal qualifies spectral mask specifications.

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300 W GaN power amplifier for LTE applications Department of Radio Science and Engineering, Chungnam National University, 99 Daehak-ro, Yuseong-gu, Daejeon, 34134, Republic of Korea Radio-Frequency Integration Technology (RFIT), 2017 IEEE International Symposium on https://doi.org/10.1109/RFIT.2017.8048244

This paper presents a 300 W GaN power amplifier operating in the LTE band 7 (2.62∼2.69 GHz). From the loadpull simulation, optimum impedances of the GaN HEMT at the fundamental frequency and the second harmonic frequency are extracted for a maximum output power. The matching circuits that give the nearly optimum second harmonic impedances are implemented on a titanate substrate with a high dielectric constant and are integrated with a bare GaN transistor in a ceramic package. The fabricated power amplifier shows a saturated output power of 258∼324 W and a drain efficiency of 67∼73 % under the pulsed condition of 1 msec period and 10 % duty cycle. It also has an output power of 80∼85 W and a drain efficiency of 42∼49 % at ACLR of 30 dBc with the LTE input signal. Recent progresses in R&D and production of GaN HEMT based power amplifiers Wavice Inc., Hwasung-si Korea Agency for Defense Development, Daejeon-si Korea Radio-Frequency Integration Technology (RFIT), 2017 IEEE International Symposium on https://doi.org/10.1109/RFIT.2017.8048090

This report describes recent progresses in development and production of GaN HEMT based power amplifiers in Wavice Inc., such as discrete transistors, s-band internally matched packaged transistors, 5W 3.5 GHz Doherty amplifiers, S-band Tx module and 4kW C-band high power amplifiers. Especially for s-band internally matched transistors and power amplifiers, more than 1500 products have been produced and qualified. The RF performance variations and reliability data from the qualification of power amplifiers are summarized. Ultra-wideband efficient linearized 10W GaN-HEMT power amplifier Microwave Engineering Laboratoiy, Berlin Institute of Technology, Berlin, Germany GloMic GmbH, Berlin, Germany

Radio-Frequency Integration Technology (RFIT), 2017 IEEE International Symposium on https://doi.org/10.1109/RFIT.2017.8048245

This paper contributes a design of an ultrawideband, high efficiency and linearized 10 W GaN-HEMT power amplifier (PA). A systematic design approach using simulation-based source- and load-pull analyses in order to find optimum load and source impedances was applied for the proposed PA. Under continuous wave (CW) large-signal measurements, the design is confirmed by experimental results, which show a state-of-the-art achievement of 165.2% fractional bandwidth (FBW) from 0.4 to 4.2 GHz with output power greater than 10 W. The moderate gain is fiat at 10.7 ± 1 dB, and the power added efficiency (PAE) stays in the range of 47–80%. Investigation of GaN channel thickness on the channel mobility in AlGaN/GaN HEMTs grown on sapphire substrate RF/Power Components Research Group, Electrics and Telecommunications Research Institute, Daejeon 34129, South Korea Electrical Engineering, Yale University, New Haven, Connecticut 06511, USA School of electronics Engineering, Kyungpook National University, Daegu 702-701, South Korea Discrete Development Team, System LSI, Samsung Electronics Co., Ltd., Yongin, Gyeonggi 446-920, South Korea Radio-Frequency Integration Technology (RFIT), 2017 IEEE International Symposium on https://doi.org/10.1109/RFIT.2017.8048091

We have invented a novel channel mobility extraction method in the gated region of AlGaN/GaN high-electron-mobility transistors (HEMTs). The resistances in the contact, gated, and access region were extracted from Id(Vg) measurements on a set of HEMTs with various gate-to-drain distances and gate lengths. By considering the impact of the access and contact resistances, an accurate model to describe the channel mobility behavior in the gated region has been achieved. This channel mobility extraction method has been employed for different GaN channel thickness devices to study the effect of the GaN channel thickness on the device performance. Our systematic measurements have revealed that the channel mobility increases up to a certain channel thickness due to the reduced edge-type dislocation

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density evidenced by the X-ray diffraction measurement data. A 1.7-GHz GaN MMIC Doherty power amplifier using an adaptive bias circuit with a quadrature coupler Department of Electrical Engineering, KAIST, Daejeon, Republic of Korea Samsung Electronics Co. Ltd, Suwon, Republic of Korea Radio-Frequency Integration Technology (RFIT), 2017 IEEE International Symposium on https://doi.org/10.1109/RFIT.2017.8048092

A 2-stage 1.7-GHz Doherty power amplifier (PA) with an adaptive bias (ADB) circuit was designed for small-cell base station applications. An uneven power cell size ratio was used to provide a large back-off efficiency for high peak-to-average power ratio (PAPR) signals. To simplify the power divider and inter-stage matching network, a lumped Lange-type quadrature coupler was used. The leakage signal from the isolated port of the coupler was used as an input signal for the ADB circuit of the peaking amplifier. The PA was implemented in a 0.25-μm GaN on a SiC MMIC process. For a 1.7-GHz continuous wave, the PA has a 45.8% power added efficiency (PAE) at the output power of 38.6-dBm and a 31.2% PAE at 7-dB back-off power. For an LTE downlink signal, adjacent channel leakage ratio (ACLR) of −25.9-dBc was obtained at the average output power of 31.4-dBm without a digital pre-distortion (DPD). A high temperature variable gain amplifier based on GaN HEMT devices for downhole communications Multifunctional Integrated Circuits and Systems (MICS) group, Bradley Department of Electrical and Computer Engineering, Virginia Tech, Blacksburg, VA 24061, USA Circuits and Systems (ISCAS), 2017 IEEE International Symposium on https://doi.org/10.1109/ISCAS.2017.8050376

The decay of easily accessible reserves pushes the oil and gas industry to explore deeper wells, where the ambient temperature often exceeds 210 °C. The need for high temperature operation, combined with real-time data logging, results in a growing demand for robust, high temperature RF circuits. This paper presents a high temperature IF variable gain amplifier (VGA) for downhole communications, which is capable of operating at 230 °C. The proposed VGA is prototyped using GaN on SiC HEMT technology. Measured results at 230 °C show that the VGA has a

peak gain of 27 dB at the center frequency of 97.5 MHz, and a dynamic range of 29.4 dB. The input P1dB compression at the peak gain is −11.57 dBm at 230 °C, and −3.63 dBm at 25 °C. The input and output return losses are above 12 dB across the entire temperature range from 25 °C to 230 °C. The maximum power gain and dynamic range drop by 1 dB and 4.7 dB, respectively, at 230 °C. The maximum power dissipation of the VGA is 176 mW under the peak gain at 230 °C. High temperature VCO based on GaN devices for downhole communications Multifunctional Integrated Circuits and System (MICS) Group Bradley Department of Electrical and Computer Engineering Virginia Tech, Blacksburg, Virginia, 24061, USA Circuits and Systems (ISCAS), 2017 IEEE International Symposium on https://doi.org/10.1109/ISCAS.2017.8050448

This paper presents a high temperature voltage-controlled oscillator (VCO) for downhole communications. The proposed VCO adopts the common-source Colpitts oscillator configuration. The VCO is prototyped using 0.25 μm GaN RF transistors due to the high junction temperature and high unity gain frequency. Two GaN varactors are used to achieve the tuning frequency range of 40 MHz up to 230 oC. The measurements at 230 oC show that the VCO has an output power of 17.5 dBm with ±0.5 dB variations over the tuning range from 320.8 to 360.2 MHz. The measured phase noise is −121 dBc/Hz at 100 kHz offset from 343.3 MHz carrier. The maximum power consumption of the VCO is 122.5 mW. Large-signal modeling of GaN devices with emphasis on trapping effect and simulation validation (Invited) MESIC, Uni. of Sci. and Tech. of China (USTC), Hefei, Anhui, China Dynax Semiconductor, Inc, Kunshan, Jiangsu, China Applied Computational Electromagnetics Society Symposium (ACES), 2017 International http://ieeexplore.ieee.org/document/8051875/

This paper will present the recent development of large-signal modeling cum PA design based on Dynax GaN HEMT devices. A modified Angelov model is used to model the pulse I-V data. Improved modeling results to address the trapping effect will be given together with new model parameter extraction

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methodology. A new Large Signal model purpose with trapping effect. Design Power Amplifier in the purpose model and compare with the measurements with old large signal model. Effect of polarization Coulomb field scattering on device linearity in AlGaN/GaN heterostructure field-effect transistors School of Microelectronics, Shandong University, Jinan 250100, China National Key Laboratory of Application Specific Integrated Circuit (ASIC), Hebei Semiconductor Research Institute, Shijiazhuang 050051, China Journal of Applied Physics http://dx.doi.org/10.1063/1.5005518

The power gain for the AlGaN/GaN heterostructure field-effect transistors (HFETs) has been measured, and a distinct difference of device linearity for a single device under two types of direct current quiescent points was observed. Based on the analyses of the variation of the transconductance and the parasitic source access resistance, it is found that polarization Coulomb field scattering can affect the power gain and the device linearity. We show that this is an effective approach to improve the linearity of AlGaN/GaN HFETs. FEM thermal and stress analysis of bonded GaN-on-diamond substrate Key Laboratory for Physical Electronics and Devices of the Ministry of Education and Key Laboratory of Photonics Technology for Information of Shaanxi Province, School of Electronics and Information Engineering, Xi’an Jiaotong University, Xi’an 710049, P.R. China Wide Band Gap Semiconductor Research Center, Xi’an Jiaotong University, Xi’an 710049, PR China ISCAS-XJTU Joint Laboratory of Functional Materials and Devices for Informatics, School of Electronics and Information Engineering, Xi’an Jiaotong University, Xi’an 710049, P.R. China AIP Advances http://dx.doi.org/10.1063/1.4995005

A three-dimensional thermal and stress analysis of bonded GaN on diamond substrate is investigated using finite element method. The transition layer thickness, thermal conductivity of transition layer, diamond substrate thickness and the area ratio of diamond and GaN are considered and treated appropriately in the numerical simulation. The maximum channel temperature of GaN is set as a

constant value and its corresponding heat power densities under different conditions are calculated to evaluate the influences that the diamond substrate and transition layer have on GaN. The results indicate the existence of transition layer will result in a decrease in the heat power density and the thickness and area of diamond substrate have certain impact on the magnitude of channel temperature and stress distribution. Channel temperature reduces with increasing diamond thickness but with a decreasing trend. The stress is reduced by increasing diamond thickness and the area ratio of diamond and GaN. The study of mechanical and thermal properties of bonded GaN on diamond substrate is useful for optimal designs of efficient heat spreader for GaN HEMT. Fabrication and comparative study of DC and low frequency noise characterization of GaN/AlGaN based MOS-HEMT and HEMT Department of Electrical and Computer Engineering, George Mason University, 4400 University Drive, Fairfax, Virginia 22030 Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, Maryland 20742 Division of Electrical and Computer Engineering, Louisiana State University, Baton Rouge, Louisiana 70803 Department of Electrical and Computer Engineering, George Mason University, 4400 University Drive, Fairfax, Virginia 22030 Journal of Vacuum Science & Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phenomena http://dx.doi.org/10.1116/1.4998937

This work presents the effect of Al mole fraction and gate oxide on the direct current and low frequency noise characterization of GaN/AlGaN high electron mobility transistor (HEMT). Metal–oxide–semiconductor (MOS)-HEMT with SiO2 in the gate stack improved the Id(on)/Id(off) ratio up to more than 8 orders, compared to fabricated HEMT without oxide. It was shown that the gate leakage and isolation leakage suppression efficiency improved dramatically with the gate oxide. Subthreshold swing of MOS-HEMTs with different Al mole fractions (from 20% to 35%) varies slightly from 72 mV/decade to 79 mV/decade. Low frequency noise study revealed the difference in transport mechanism between HEMT and MOS-HEMTs. By using carrier number fluctuation model on the measured data, it was found that the noise is predominantly coming from

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the surface states. While generation-recombination is very prominent in HEMT, it is very insignificant in both MOS-HEMTs at much higher frequencies. This study reveals that very high number of surface states, assisting the tunneling in Schottky/AlGaN barrier is responsible for unusually high leakage and higher noise level in HEMT without oxide. Leakage level is improved from mA/mm range for HEMT to pA/mm range for MOS-HEMTs. Leakage suppression improvement and minimization of noise level can be mainly attributed by to high quality SiO2. Hooge's constant was on the order of 5–6 × 10−3, which is 5 × 10−2 for HEMT without oxide. Trap states analysis in AlGaN/AlN/GaN and InAlN/AlN/GaN high electron mobility transistors Laboratoire de Micro-Optoélectroniques et Nanostructures, Faculté des Sciences de Monastir, Avenue de l'environnement, 5019 Monastir, Tunisia Université Côte d'Azur, CNRS- CRHEA, Rue Bernard Grégory, 06560, Valbonne, France Institut d'Electronique, de Microélectronique et Nanotechnologies (IEMN), Cité Scientifique, 59650, Villeneuve d'Ascq, France Current Applied Physics https://doi.org/10.1016/j.cap.2017.09.003

The paper deals with trap effects in InAlN/AlN/GaN and AlGaN/AlN/GaN high electron mobility transistor structures using frequency dependent conductance and High-Low frequency capacitance analysis. We performed a comparative study on electrical characteristics of electron devices. Capacitance-voltage characteristics revealed hysteresis with a voltage shift that was attributed to the accumulation of charges at the InAlN/AlN and AlGaN/AlN heterointerfaces. Using a simple extraction method, a rather low density of trapped charges is evaluated. On the other hand, bias and frequency dependent measurements are carried out in the vicinity of threshold voltage to determine the interface trap density Dit, trap time constant τit and trap state energy position ET. It is found that device with InAlN barrier exhibits high trap state densities in the range of 1012 -1014 cm−2eV−1, approximately one order of magnitude larger than with AlGaN barrier. Barrier-Layer Optimization for Enhanced GaN-on-Diamond Device Cooling Center for Device Thermography and Reliability (CDTR), H. H. Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Bristol BS8 1TL, U.K.

Qorvo Inc., 500 W. Renner Road, Richardson, Texas 75080, United States Fraunhofer, USA Center for Coatings and Diamond Technologies, East Lansing, Michigan 48824, United States Michigan State University, East Lansing, Michigan 48824, United States ACS Appl. Mater. Interfaces http://dx.doi.org/10.1021/acsami.7b08961

GaN-on-diamond device cooling can be enhanced by reducing the effective thermal boundary resistance (TBReff) of the GaN/diamond interface. The thermal properties of this interface and of the polycrystalline diamond grown onto GaN using SiN and AlN barrier layers as well as without any barrier layer under different growth conditions are investigated and systematically compared for the first time. TBReff values are correlated with transmission electron microscopy analysis, showing that the lowest reported TBReff (∼6.5 m2 K/GW) is obtained by using ultrathin SiN barrier layers with a smooth interface formed, whereas the direct growth of diamond onto GaN results in one to two orders of magnitude higher TBReff due to the formation of a rough interface. AlN barrier layers can produce a TBReff as low as SiN barrier layers in some cases; however, their TBReff are rather dependent on growth conditions. We also observe a decreasing diamond thermal resistance with increasing growth temperature. High Frequency Noise Model of AlGaN/GaN HEMTs School of Electronic Engineering, University of Electronic Science and Technology of China, Chengdu, People's Republic of China Hiwafer Semiconductor Co., Ltd., Chengdu, People's Republic of China National Key Laboratory of Science and Technology on Space Microwave, China Academy of Space Technology, Xi'an, People's Republic of China ECS J. Solid State Sci. Technol. http://dx.doi.org/10.1149/2.0171711jss

Compared with conventional GaAs HEMTs, the larger gate leakage current and more obviously self-heating effects are two unique macroscopic features in AlGaN/GaN HEMTs. This paper presents the study of the effects brought by temperature-dependent Rs and Rd on noise performance of AlGaN/GaN HEMT. Based on these studies, a noise model up to 35GHz is established. An improved PRC model is proposed and the noise parameters NFmin, Rn and Γopt in the frequency band ranging from 0.1GHz to 35GHz is

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investigated. The effects brought by gate leakage current have been taken into consideration. Then, noise performance under different ambient temperature has been studied based on the high frequency noise model mentioned above. The parameters in the model except the parasitic inductors and capacitors are all temperature-dependent. With the model, the effects brought by temperature-dependent Rs and Rd have been studied under four different temperatures by comparing the noise performance in two different conditions. Results show that the temperature-dependent characteristics of these two parasitic resistances will have an effect on NFmin and Rn while little effect on Γopt. The influence of gate length on the electron injection of velocity in an AlGaN/AlN/GaN НЕМТ channel Institute of Ultrahigh-Frequency Semiconductor Electronics, Russian Academy of Sciences, Moscow, Russia Technical Physics Letters https://doi.org/10.1134/S1063785017080235

Field-effect high-electron-mobility transistors (HEMTs) based on AlGaN/AlN/GaN heterostructures with various gate lengths Lg have been studied. The maximum values of current and power gaincutoff frequencies (fT and fmax, respectively) amounted to 88 and 155 GHz for HEMTs with Lg = 125 nm, while those for the transistors with Lg = 360 nm were 26 and 82 GHz, respectively. Based on the measured S-parameters, the values of elements in small-signal equivalent schemes of AlGaN/AlN/GaN HEMTs were extracted and the dependence of electron-injection velocity vinj on the gate–drain voltage was determined. The influence of Lg and the drain–source voltage on vinj has been studied. Nonalloyed ohmic contacts for high-electron-mobility transistors based on AlGaN/GaN heterostructures Institute of Microwave Semiconductor Electronics, Russian Academy of Sciences, Moscow, Russia Russian Microelectronics https://doi.org/10.1134/S1063739717050079

A microwave field-effect transistor with nonalloyed ohmic contacts is fabricated using the technique of regrowing a heavily doped region under the contact metallization by molecular beam epitaxy through a

preliminarily formed dielectric mask. The fabricated field-effect transistor with a gate length of 0.18 µm and a total width of 100 µm has a current–amplification cutoff frequency of 66 GHz and ohmic contact resistivity of 0.15-0.18 Ω mm. Characterization of 0.18-μm gate length AlGaN/GaN HEMTs on SiC fabricated using two-step gate recessing Photonic-Wireless Convergence Components Research Department, ICT Materials & Components Research Laboratory, Electronics and Telecommunications Research Institute, Daejeon, Korea Journal of the Korean Physical Society https://doi.org/10.3938/jkps.71.360

We fabricated a 0.18-μm gate-length AlGaN/GaN high electron mobility transistor (HEMT) on SiC substrate fabricated by using two-step gate recessing which was composed of inductively coupled plasma (ICP) dry etching with a gas mixture of BCl3/Cl2 and wet chemical etching using the oxygen plasma treatment and HCl-based cleaning. The two-step gate recessing process exhibited an etch depth of 4.5 nm for the AlGaN layer and the clean surface of AlGaN layer at the AlGaN/gate metal contact region for the AlGaN/GaN HEMT structure. The recessed 0.18 μm × 200 μm AlGaN/GaN HEMT devices showed good DC characteristics, having a good Schottky diode ideality factor of 1.25, an extrinsic transconductance (gm) of 345 mS/mm, and a threshold voltage (Vth) of −2.03 V. The recessed HEMT devices exhibited high RF performance, having a cut-off frequency (fT) of 48 GHz and a maximum oscillation frequency (fmax) of 130 GHz. These devices also showed minimum noise figure of 0.83 dB and associated gain of 12.2 dB at 10 GHz. Characteristics of enhanced-mode AlGaN/GaN MIS HEMTs for millimeter wave applications RF Convergence Components Research Section, IT Materials and Components LaboratoryElectronics and Telecommunications Research InstituteDaejeonKorea Journal of the Korean Physical Society https://doi.org/10.3938/jkps.71.365

In this paper, an enhanced-mode (E-mode) AlGaN/GaN high electron mobility transistor (HEMT) was developed by using 4-inch GaN HEMT process. We designed and fabricated Emode HEMTs and characterized device performance. To estimate the

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possibility of application for millimeter wave applications, we focused on the high frequency performance and power characteristics. To shift the threshold voltage of HEMTs we applied the Al2O3 insulator to the gate structure and adopted the gate recess technique. To increase the frequency performance the e-beam lithography technique was used to define the 0.15 um gate length. To evaluate the dc and high frequency performance, electrical characterization was performed. The threshold voltage was measured to be positive value by linear extrapolation from the transfer curve. The device leakage current is comparable to that of the depletion mode device. The current gain cut-off frequency and the maximum oscillation frequency of the E-mode device with a total gate width of 150 um were 55 GHz and 168 GHz, respectively. To confirm the power performance for mm-wave applications the load-pull test was performed. The measured power density of 2.32 W/mm was achieved at frequencies of 28 and 30 GHz. Simulation study of InAlN/GaN high-electron mobility transistor with AlInN back barrier School of Electronic and Information Engineering, Hebei University of Technology, Tianjin 300401, China Chinese Physics B https://doi.org/10.1088/1674-1056/26/10/107301

In this work, we use a 3-nm-thick Al0.64In0.36N back-barrier layer in In0.17Al0.83N/GaN high-electron mobility transistor (HEMT) to enhance electron confinement. Based on two-dimensional device simulations, the influences of Al0.64In0.36N back-barrier on the direct-current (DC) and radio-frequency (RF) characteristics of InAlN/GaN HEMT are investigated, theoretically. It is shown that an effective conduction band discontinuity of approximately 0.5 eV is created by the 3-nm-thick Al0.64In0.36N back-barrier and no parasitic electron channel is formed. Comparing with the conventional InAlN/GaN HEMT, the electron confinement of the back-barrier HEMT is significantly improved, which allows a good immunity to short-channel effect (SCE) for gate length decreasing down to 60 nm (9-nm top barrier). For a 70-nm gate length, the peak current gain cut-off frequency (f T) and power gain cut-off frequency (f max) of the back-barrier HEMT are 172 GHz and 217 GHz, respectively, which are higher than those of the conventional HEMT with the same gate length.

Characterization of N-polar AlN in GaN/AlN/(Al,Ga)N heterostructures grown by metal-organic chemical vapor deposition Electrical & Computer Engineering and Materials Departments, University of California, Santa Barbara, CA 93106, United States of America Center for Nanophase Materials Science, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6139, United States of America Semiconductor Science and Technology https://doi.org/10.1088/1361-6641/aa8b30

In GaN/(Al,Ga)N high-electron-mobility transistors (HEMT), AlN interlayer between GaN channel and AlGaN barrier suppresses alloy scattering and significantly improves the electron mobility of the two-dimensional electron gas. While high concentrations of gallium were previously observed in Al-polar AlN interlayers grown by metal-organic chemical vapor deposition, the N-polar AlN (Al x Ga1−x N) films examined by atom probe tomography in this study exhibited aluminum compositions (x) equal to or higher than 95% over a wide range of growth conditions. The also investigated AlN interlayer in a N-polar GaN/AlN/AlGaN/ S.I. GaN HEMT structure possessed a similarly high x content. Effect of Surface Passivation on the Electrical Characteristics of Nanoscale AlGaN/GaN HEMT Department of Electronics and Communication Engineering, Amity School of Engineering and Technology Amity Institute of Telecommunication and Management, Amity University Uttar Pradesh-201313, India IOP Conference Series: Materials Science and Engineering https://doi.org/10.1088/1757-899X/225/1/012095

In this paper, we present the effect of passivation layer on the electrical characteristics of AlGaN/GaN HEMT. The energy band diagram, drain current voltage characteristics, transconductance and cut off frequency was calculated for both long channel and short channel devices. It was found that the electrical characteristics of the device improve with the introduction of high K dielectric in the passivation layer. The results obtained agree well with the data available in literature.

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Electron mobility in abrupt-interface and step-graded AlGaN/GaN Heterostructures School of Information Engineering, Guangdong University of Technology, Guangzhou, 510006, People's Republic of China Department of Physics, College of Physics and Electrical Engineering, Guangzhou University, Guangzhou 510006, People's Republic of China Semiconductor Science and Technology https://doi.org/10.1088/1361-6641/aa84d8

Based on the ensemble Monte Carlo method, we present a comparative study of the electron mobility of two-dimensional electron gases (2DEGs) formed in AlGaN/GaN abrupt-interface heterostructures (ABHs) and step-graded heterostructures (SGHs) at room temperature. We find that the electron mobility in SGHs is obviously higher than that in ABHs. The dependence of electron mobilities on the AlGaN barrier thickness is found to have a close relationship with the dislocation scatterings of electrons. On the other hand, our calculated results show that the mobility difference between SGHs and ABHs generally increases with AlGaN barrier thickness, which means that SGHs with a thicker barrier layer play a more prominent role in obtaining high mobility, compared with ABH counterparts.

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GROUP 5 – MEMS and Sensors Group leader: Marc Faucher (IEMN) Information selected by Knowmade

Analysis of a MEMS Tuned Cavity Oscillator on X -Band Department of Microtechnology and Nanoscience, Microwave Electronics Laboratory, Chalmers University of Technology, Gothenburg, Sweden IEEE Transactions on Microwave Theory and Techniques https://doi.org/10.1109/TMTT.2017.2683491

This paper reports on the analysis of a radio frequency microelectromechanical systems (RF-MEMS) tuned cavity oscillator on X -band based on a GaN-HEMT monolithic microwave integrated circuit reflection amplifier. The RF-MEMS-switches are mounted on a low-loss printed circuit board (PCB) intruded in an aluminum cavity that is coupled to a microstrip line connected to the reflection amplifier. This paper investigates the influence of the number of switches as well as their positions with respect to phase noise and tuning range. Vertical and horizontal positions of the switches are varied with target on optimum trade-off between phase noise and total tuning range. For a three-row MEMS-configuration at 1-mm depth from the end cavity wall, a tuning range of 4.9% is measured. The center frequencies are ranging from 9.84 to 10.33 GHz with measured phase noise of −140 to −129 dBc/Hz at 100-kHz offset. A similar three-row MEMS setup at 2.5-mm depth provides a tuning range of 12.3% with measured phase noise of −133 to −123 dBc/Hz at 100-kHz offset. Chip-Scale Near-Field Resonant Power Transfer via Elastic Waves Department of Electrical and Computer Engineering, Carnegie Mellon University, Pittsburgh, PA, USA Journal of Microelectromechanical Systems https://doi.org/10.1109/JMEMS.2017.2719944

This paper reports on the proof-of-concept demonstration of an approach for the synthesis of a through package charging and authenticating communication link enabled by GHz-range aluminum nitride (AlN) piezoelectric transducers. The acoustic link is formed by two thickness-mode acoustic transducers placed on the two sides of a packaging substrate. The link leverages the enhancement of

energy transfer that occurs at resonance; 1- μm -thick (2.7 GHz) and 6- μm -thick (500 MHz) AlN acoustic links are demonstrated showing substantial enhancement of power transfer efficiencies (PTE) when using thicker AlN substrates. PTEs of −8 dB at 2.7 GHz and −2 dB at 500 MHz are measured for transducers’ size of 1×100×100 μm3 and 6×100×100 μm3 through 700- and 500- μm -thick silicon substrates, respectively. The experimental values are in very close agreement with the analytical model of the acoustic link. The potential misalignment between the two transducers is the main limitation of this approach. To overcome this challenge, acoustic phased arrays are devised to enable steering of the transmitted beam. Preliminary results on the steering capability demonstrate about 8 dB of improvement in PTE via a two-element array when dealing with a 100- μm misalignment. This paper is the first step toward the development of next-generation high-efficiency and micro-scale power transfer units that could energize chips through packages. Fabrication and Electromechanical Modeling of a Flexural-Mode MEMS Piezoelectric Transformer in AlN Department of Electrical, Electronic, and Information Engineering, Advanced Research Center on Electronic Systems, University of Bologna, Cesena, Italy Centre of Materials and Microsystems, Fondazione Bruno Kessler, Trento, Italy Institute for Sensors and Actuators Systems, Vienna University of Technology, Vienna, Austria Journal of Microelectromechanical Systems https://doi.org/10.1109/JMEMS.2017.2709407

This paper presents the fabrication and electromechanical characterization of a novel AlN-based microelectromechanical systems (MEMS) flexural-mode piezoelectric transformer (PT) realized in a silicon-on-insulator bulk-micromachining process with segmented electrodes at the secondary side, which are series-connected in order to increase the output voltage. The goal of this work is to propose a MEMS-based alternative to inductors and magnetic transformers for power management in micro-power mm-scale electronic systems. The fabricated device is fully modeled by means of the Butterworth-Van Dyke

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(BVD) two-port network. The device is modeled analytically with the classic equations of a fully clamped-edge membrane and through finite-element method simulations. Characterization is performed through impedance measurements and an alternative empirical method suitable for MEMS devices is proposed for directly extracting its lumped parameters electromechanical circuit. Finally, the effect of the feed-through capacitance is fully analytically modeled, and this paper presents a variant of the BVD network of the PT with an inner BVD circuit, allowing an easier estimation of the effects of the complex zeros introduced by the feed-forward capacitance. The presented device achieves a measured maximum voltage gain of 58mV/V at ~36.3 kHz and maximum efficiency of ~75%. GaN membrane supported SAW pressure sensors with embedded temperature sensing capability IMT-Bucharest, 32B Erou Iancu Nicolae street, R-07719, Bucharest, Romania FORTH IESL Heraklion, Crete, Greece IEEE Sensors Journal https://doi.org/10.1109/JSEN.2017.2757770

This paper presents the fabrication and characterization of a GHz operating SAW based pressure sensor on a 1.2 μm thin GaN membrane. Two types of interdigitated transducers are manufactured using electron beam nanolithography to obtain finger and interdigit spacing widths - one with 170 nm and the other 200 nm half pitch. Micromachining techniques are used to obtain the 1.2 μm thin membrane. The resonance frequency shift of the SAW, the pressure sensitivity, sp, as well as the pressure coefficient of frequency, PCF, were experimentally determined and analyzed, both for the Rayleigh as well as for the symmetrical Lamb propagation mode, in the 1 to 7 Bar pressure range. Record values for sp (up to 6 MHz/Bar) and PCF (up to 537 ppm/Bar) have been obtained, especially for the symmetrical Lamb propagation mode also due to the very high frequency operation (5-11.5 GHz). The effect of different orientations of the SAW device (in the [1100] and [1120] directions) on the frequency response and sensitivity is also analyzed. The possibility to determine simultaneously the pressure and the temperature with the same SAW structure operating as a dual sensor has been demonstrated.

Design, Fabrication, and Characterization of Scandium Aluminum Nitride-Based Piezoelectric Micromachined Ultrasonic Transducers Department of Mechanical and Aerospace Engineering, University of California at Davis, Davis, CA, USA Advanced Modular Systems, Inc., Goleta, CA, USA Journal of Microelectromechanical Systems https://doi.org/10.1109/JMEMS.2017.2712101

This paper presents the design, fabrication, and characterization of piezoelectric micromachined ultrasound transducers (PMUTs) based on scandium aluminum nitride (ScxAl1–xN) thin films (x = 15%). ScAlN thin film was prepared with a dual magnetron system and patterned by a reactive ion etching system utilizing chlorine-based chemistry with an etching rate of 160 nm/min. The film was characterized by X-ray diffraction, which indicated a crystalline structure expansion compared with pure AlN and a well-aligned ScAlN film. ScAlN PMUTs were fabricated by a two-mask process based on cavity SOI wafers. ScAlN PMUTs with 50- and 40- μm diameter had a large dynamic displacement sensitivity measured in air of 25 nm/V at 17 MHz and 10 nm/V at 25 MHz, twice that of AlN PMUTs with the same dimensions. The peak displacement as a function of electrode coverage was characterized, with maximum displacement achieved with an electrode radius equal to 70% of the PMUT radius. Electrical impedance measurements indicated that the ScAlN PMUTs had 36% greater electromechanical coupling coefficient ( k2t) compared with AlN PMUTs. The output pressure of a 7×7 ScAlN PMUT array was 0.7 kPa/V at ~1.7 mm away from the array, which is approximately three times greater that of an 8×8 AlN PMUT array with the same element geometry and fill factor measured at the same distance. Acoustic spreading loss and PMUT insertion loss from mechanical transmit to receive were characterized with a 15 × 15 ScAlN PMUT array via hydrophone and laser Doppler vibrometer. Tuning the piezoelectric and mechanical properties of the AlN system via alloying with YN and BN Department of Mechanical Engineering, Colorado School of Mines, Golden, Colorado 80401, USA Department of Metallurgical and Materials Engineering, Colorado School of Mines, Golden, Colorado 80401, USA Journal of Applied Physics http://dx.doi.org/10.1063/1.4993254

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Recent advances in microelectromechanical systems often require multifunctional materials, which are designed so as to optimize more than one property. Using density functional theory calculations for alloyed nitride systems, we illustrate how co-alloying a piezoelectric material (AlN) with different nitrides helps tune both its piezoelectric and mechanical properties simultaneously. Wurtzite AlN-YN alloys display increased piezoelectric response with YN concentration, accompanied by mechanical softening along the crystallographic c direction. Both effects increase the electromechanical coupling coefficients relevant for transducers and actuators. Resonator applications, however, require superior stiffness, thus leading to the need to decouple the increased piezoelectric response from the softened lattice. We show that co-alloying of AlN with YN and BN results in improved elastic properties while retaining some of the piezoelectric enhancements from YN alloying. This finding may lead to new avenues for tuning the design properties of piezoelectrics through composition-property maps. Giant increase in piezoelectric coefficient of AlN by Mg-Nb simultaneous addition and multiple chemical states of Nb Advanced Manufacturing Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), 807-1, Tosu, Saga 841-0052, Japan Department of Molecular and Material Sciences, Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, 6-1, Kasuga-kouen, Kasuga, Fukuoka 816-8580, Japan Murata Manufacturing Co., Ltd., 1-10-1, Higashikoutari, Nagaokakyo, Kyoto 617–8555, Japan Appl. Phys. Lett. http://dx.doi.org/10.1063/1.4990533

Aluminum nitride (AlN) is one of piezoelectric materials, which are eagerly anticipated for use in microelectromechanical systems (MEMS) applications such as communication resonators, sensors, and energy harvesters. AlN is particularly excellent in generated voltage characteristics for the MEMS rather than oxide piezoelectric materials such as lead zirconium titanate Pb(Zr, Ti)O3. However, it is necessary to improve the piezoelectric properties of AlN in order to advance the performance of the MEMS. We dramatically increased the piezoelectric coefficient d33 of AlN films by simultaneously adding magnesium (Mg) and niobium (Nb). The d33 of Mg39.3Nb25.0Al35.7N is 22 pC/N, which is about

four times that of AlN. The d33 is increased by Mg and Nb simultaneous addition, and is not increased by Mg or Nb single addition. Interestingly, the Nb has multiple chemical states, and which are influenced by the Mg concentration. High-performance ultraviolet photodetectors based on lattice-matched InAlN/AlGaN heterostructure field-effect transistors gated by transparent ITO films Research Center for Nano Devices and Advanced Materials, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555, Japan Appl. Phys. Lett. http://dx.doi.org/10.1063/1.4986311

We demonstrate high-performance ultraviolet photodetectors (UV-PDs) based on lattice-matched (LM) InAlN/AlGaN heterostructure field-effect transistors (HFETs) gated by transparent ITO films. Low dark currents of 6.8 × 10−8 and 6.1 × 10−7 A/mm and high photocurrent gains over four and three orders of magnitude were obtained for the LM In0.12Al0.88N/Al0.21Ga0.79N and In0.10Al0.90N/Al0.34Ga0.66N HFETs, respectively. The negative threshold voltage shifts under illumination indicate that most of the photo-generated carriers are transported in the two-dimensional gas (2DEG) region around the InAlN/AlGaN interface. High peak responsivities of 2.2 × 104 and 5.4 × 104 A/W and large UV-to-visible rejection ratios greater than 104 and 103 were achieved for the LM In0.12Al0.88N/Al0.21Ga0.79N and In0.10Al0.90N/Al0.34Ga0.66N HFET-type UV-PDs, respectively. These improved performances with respect to other AlGaN UV-PDs around the same wavelength detection range may possibly be attributed to the greater contribution of the photogenerated electrons to the 2DEG, which results from the increase in the polarization sheet charge density at the InAlN/AlGaN interface. The LM InAlN/AlGaN heterostructures provide relatively promising candidates for realizing high-performance HFET-type UV-PDs. High sensitivity cardiac troponin I detection in physiological environment using AlGaN/GaN High Electron Mobility Transistor (HEMT) Biosensors Institute of NanoEngineering and Microsystems, National Tsing Hua University, Hsinchu 300, Taiwan R.O.C Department of Power Mechanical Engineering, National Tsing Hua University, Hsinchu 300, Taiwan R.O.C

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Institute of Biomedical Engineering, National Tsing Hua University, Hsinchu 300, Taiwan R.O.C Department of Electrical Engineering, National Central University, Jhongli City, Taoyuan County 320, Taiwan R.O.C Department of Medical Laboratory Science and Biotechnology, National Cheng-Kung University, Tainan City 701, Taiwan R.O.C Biosensors and Bioelectronics https://doi.org/10.1016/j.bios.2017.09.018

In this study, we report the development of a high sensitivity assay for the detection of cardiac troponin I using electrical double layer gated high field AlGaN/GaN HEMT biosensor. The unique gating mechanism overcomes the drawback of charge screening seen in traditional FET based biosensors, allowing detection of target proteins in physiological solutions without sample processing steps. Troponin I specific antibody and aptamer are used as receptors. The tests carried out using purified protein solution and clinical serum samples depict high sensitivity, specificity and wide dynamic range (0.006–148 ng/mL). No additional wash or sample pre-treatment steps are required, which greatly simplifies the biosensor system. The miniaturized HEMT chip is packaged in a polymer substrate and easily integrated with a portable measurement unit, to carry out quantitative troponin I detection in serum samples with<2 µl sample volume in 5 min. The integrated prototype biosensor unit demonstrates the potential of the method as a rapid, inexpensive, high sensitivity CVD biomarker assay. The highly simplified protocols and enhanced sensor performance make our biosensor an ideal choice for point of care diagnostics and personal healthcare systems. Near-Infrared Intersubband Photodetection in GaN/AlN Nanowires Université Grenoble-Alpes, CEA, INAC, PHELIQS, 17 av. des Martyrs, 38000 Grenoble, France Université Grenoble-Alpes, CNRS, Institut Néel, 25 av. des Martyrs, 38000 Grenoble, France Nano Lett. http://dx.doi.org/10.1021/acs.nanolett.7b03414

Intersubband optoelectronic devices rely on transitions between quantum-confined electron levels in semiconductor heterostructures, which enables infrared (IR) photodetection in the 1–30 μm wavelength window with picosecond response times.

Incorporating nanowires as active media could enable an independent control over the electrical cross-section of the device and the optical absorption cross-section. Furthermore, the three-dimensional carrier confinement in nanowire heterostructures opens new possibilities to tune the carrier relaxation time. However, the generation of structural defects and the surface sensitivity of GaAs nanowires have so far hindered the fabrication of nanowire intersubband devices. Here, we report the first demonstration of intersubband photodetection in a nanowire, using GaN nanowires containing a GaN/AlN superlattice absorbing at 1.55 μm. The combination of spectral photocurrent measurements with 8-band k·p calculations of the electronic structure supports the interpretation of the result as intersubband photodetection in these extremely short-period superlattices. We observe a linear dependence of the photocurrent with the incident illumination power, which confirms the insensitivity of the intersubband process to surface states and highlights how architectures featuring large surface-to-volume ratios are suitable as intersubband photodetectors. Our analysis of the photocurrent characteristics points out routes for an improvement of the device performance. This first nanowire based intersubband photodetector represents a technological breakthrough that paves the way to a powerful device platform with potential for ultrafast, ultrasensitive photodetectors and highly efficient quantum cascade emitters with improved thermal stability. Ultraviolet-C Photodetector Fabricated Using Si-Doped n-AlGaN Nanorods Grown by MOCVD Semiconductor Materials Process Laboratory, School of Advanced Materials Engineering, Engineering College, Research Center for Advanced Materials Development (RCAMD), Chonbuk National University, Baekje-daero 567, Jeonju 54896, Republic of Korea ACS Photonics http://dx.doi.org/10.1021/acsphotonics.7b01047

Aluminum gallium nitride (AlxGa1–xN) alloy films and nanostructures have attracted extensive research attention for ultraviolet (UV) and deep ultraviolet optoelectronic applications. However, the morphology-controlled growth of high-quality AlxGa1–xN quasi one-dimensional nanostructures has been limited by the complex multicomponent phase diagram and inhomogeneous composition

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distribution. Here, we demonstrated the growth of Si-doped n-type compositionally uniform Al0.45Ga0.55N nanorods employing a metal organic chemical vapor deposition (MOCVD) technique for the application in UV-C photodetectors. A two-step growth process, namely, growth of undoped GaN seeds and subsequent growth of n-AlGaN nanorods over GaN seeds, has been developed. Various characterization techniques have been used to study the crystalline quality, orientation, and optical properties of the realized nanorods. Field emission scanning electron microscopy revealed a uniform distribution of vertically aligned n-AlGaN nanorods over the GaN seeds. X-ray diffraction studies showed that the grown nanorods are preferentially (0002) oriented with hexagonal crystal structure. High-resolution transmission electron microscopy images indicated the nanorods are single crystalline in nature, without any significant crystalline defects and dislocations. Cathodoluminescence spectra of AlGaN nanorods displayed a strong band edge excitonic emission peak at 276 nm at 77 K and shifted to lower energy as the temperature increased to 300 K. The photocurrent current (Ip) of the fabricated photoconductive device was significantly higher in the UV region (250–276 nm) compared to the corresponding dark current. The photocurrent displayed a nonlinear power density (P)-dependent characteristics (Ip ∝ P0.64). The photoresponsivity and sensitivity of the fabricated photodetector were estimated to be ∼115 mA/W and ∼64%, respectively, in the UV-C region. Selective UV photodetectors based on the metal–AlGaN Schottky barrier St. Petersburg State Electrotechnical University (LETI), St. Petersburg, Russia Journal of Communications Technology and Electronics https://doi.org/10.1134/S1064226917090194

Selective metal–AlGaN photodetectors based on the Schottky barrier and operating in UV spectral range have been developed. The selective photodiodes based on Ag–AlGaN Schottky barriers of different composition have been manufactured, which has made it possible to improve the photosensitivity in the UV spectral range and eliminate spurious signals in the long-wavelength part of the UV spectral range. This has made it possible to develop visible-blind photodetectors with the long-wavelength edge of photosensitivity lying at the wavelengths less than

350 nm. The width of the photosensitivity spectrum is within 15–40 nm, depending on the thickness of the Ag layer, which varies from 15 to 150 nm. The proper choice of the composition of the AlxGa1–xN solid solution ensures increase in the photoresponse and reduction of the FWHM spectrum width up to 11 nm by matching peaks of the Ag transmission spectrum and the absorption spectrum of the epitaxial layer. The sensitivity is 0.071 A/W. The combination of effects of wideband window and overthe- barrier transfer has made it possible to create the ultraselective UV photodetectors based on Au–AlGaN structures with a half-width of the photosensitivity spectrum of 5–6 nm for the wave range 350—375 nm and a sensitivity of up to 140 mA/W. Based on a structure with the upper AlxGa1–xN epitaxial layer (with the AlN content x = 0.1 or x = 0.06), selective photodetectors with the maximum photosensitivity at wavelengths of 355 nm and 362 nm have been developed. Application of an additional less wideband GaN layer has made it possible to independently control the short-wavelength and long-wavelength boundaries of the sensitivity range. Fast Electrical Detection of Carcinoembryonic Antigen Based on AlGaN/GaN High Electron Mobility Transistor Aptasensor Key Lab of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083 School of Microelectronics, University of Chinese Academy of Sciences, Beijing 100049 Beijing Key Laboratory of Low Dimensional Semiconductor Materials and Devices, Beijing 100083 Chinese Physics Letters https://doi.org/10.1088/0256-307X/34/9/097302

As one of the most important tumor-associated antigens of colorectal adenocarcinoma, the carcinoembryonic antigen (CEA) threatens human health seriously all over the globe. Fast electrical and highly sensitive detection of the CEA with AlGaN/GaN high electron mobility transistor is demonstrated experimentally. To achieve a low detection limit, the Au-gated sensing area of the sensor is functionalized with a CEA aptamer instead of the corresponding antibody. The proposed aptasensor has successfully detected different concentrations (ranging from 50 picogram/milliliter (pg/ml) to 50 nanogram/milliliter (ng/ml)) of CEA and achieved a detection limit as low as 50 pg/ml at $V_\mathrmds=0.5\,V$. The

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drain-source current shows a clear increase of 11.5 μA under this bias. Construction of GaN/Ga2O3 p–n junction for an extremely high responsivity self-powered UV photodetector Center for Optoelectronics Materials and Devices, Department of Physics, Zhejiang Sci-Tech University, Hangzhou 310018, China State Key Laboratory of Information Photonics and Optical Communications & Laboratory of Optoelectronics Materials and Devices, School of Science, Beijing University of Posts and Telecommunications, Beijing 100876, China J. Mater. Chem. C http://dx.doi.org/10.1039/C7TC03746E

A self-powered ultraviolet photodetector was constructed with GaN/Ga2O3 p–n junction by depositing n-type Ga2O3 thin film on Al2O3 single crystals substrate covered by p-type GaN thin film. The fabricated device exhibits a typical rectification behavior in dark and excellent photovoltaic characteristics under 365 nm and 254 nm light illumination. The device shows an extremely high responsivity of 54.43 mA W−1, a fast decay time of 0.08 s, a high Ilight/Idark ratio of 152 and a high detectivity of 1.23 × 1011 cm Hz1/2 W−1 under 365 nm light with a light intensity of 1.7 mW cm−2 under zero bias. Such excellent performances under zero bias are attributed to the rapid separation of photogenerated electron–hole pairs driven by built-in electric field in the interface depletion region of GaN/Ga2O3 p–n junction. The results strongly suggest that the GaN/Ga2O3 p–n junction based photodetectors are suitable for applications in secure ultraviolet communication and space detection which require high responsivity and self-sufficient functionality. Ethanol surface chemistry on MBE-grown GaN(0001), GaOx/GaN(0001), and Ga2O3(-201) Chair of Physical Chemistry, Department of Chemistry and Catalysis Research Center, Technische Universität München, Lichtenbergstrasse 4, 85748 Garching, Germany Nanosystems Initiative Munich (NIM), Schellingstr. 4, 80799 Munich, Germany Walter Schottky Institute and Physics Department, Technische Universität München, Am Coulombwall 4 85748 Garching, Germany The Journal of Chemical Physics http://dx.doi.org/10.1063/1.4994141

"In this work, ethanol is used as a chemical probe to study the passivation of molecular beam epitaxy-grown GaN(0001) by surface oxidation. With a high degree of oxidation, no reaction from ethanol to acetaldehyde in temperature-programmed desorption experiments is observed. The acetaldehyde formation is attributed to a mechanism based on αα-H abstraction from the dissociatively bound alcohol molecule. The reactivity is related to negatively charged surface states, which are removed upon oxidation of the GaN(0001) surface. This is compared with the Ga2O3(2⎯⎯⎯012¯01) single crystal surface, which is found to be inert for the acetaldehyde production. These results offer a toolbox to explore the surface chemistry of nitrides and oxynitrides on an atomic scale and relate their intrinsic activity to systems under ambient atmosphere. Co-adsorption of water and oxygen on GaN: Effects of charge transfer and formation of electron depletion layer Howard P. Isermann Department of Chemical and Biological Engineering, Rensselaer Polytechnic Institute, Troy, New York 12180, USA Department of Physics, Applied Physics, and Astronomy, Rensselaer Polytechnic Institute, Troy, New York 12180, USA The Journal of Chemical Physics http://dx.doi.org/10.1063/1.4991322

Species from ambient atmosphere such as water and oxygen are known to affect electronic and optical properties of GaN, but the underlying mechanism is not clearly known. In this work, we show through careful measurement of electrical resistivity and photoluminescence intensity under various adsorbates that the presence of oxygen or water vapor alone is not sufficient to induce electron transfer to these species. Rather, the presence of both water and oxygen is necessary to induce electron transfer from GaN that leads to the formation of an electron depletion region on the surface. Exposure to acidic gases decreases n-type conductivity due to increased electron transfer from GaN, while basic gases increase n-type conductivity and PL intensity due to reduced charge transfer from GaN. These changes in the electrical and optical properties, as explained using a new electrochemical framework based on the phenomenon of surface transfer doping, suggest that gases interact with the semiconductor surface through electrochemical

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reactions occurring in an adsorbed water layer present on the surface.

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GROUP 6 - Photovoltaics and Energy harvesting Group leader: Eva Monroy (INAC-CEA)

Information selected by Knowmade

Enhanced Solar Cell Conversion Efficiency of InGaN/GaN Multiple Quantum Wells by Piezo-Phototronic Effect Beijing Institute of Nanoenergy and Nanosystems, Chinese Academy of Sciences, Beijing 100083, China CAS Center for Excellence in Nanoscience, National Center for Nanoscience and Technology (NCNST), Beijing 100190, China University of Chinese Academy of Sciences, Beijing 100049, China School of Material Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, United States ACS Nano http://dx.doi.org/10.1021/acsnano.7b04935

The piezo-phototronic effect is the tuning of piezoelectric polarization charges at the interface to largely enhance the efficiency of optoelectronic processes related to carrier separation or recombination. Here, we demonstrated the enhanced short-circuit current density and the conversion efficiency of InGaN/GaN multiple quantum well solar cells with an external stress applied on the device. The external-stress-induced piezoelectric charges generated at the interfaces of InGaN and GaN compensate the piezoelectric charges induced by lattice mismatch stress in the InGaN wells. The energy band realignment is calculated with a self-consistent numerical model to clarify the enhancement mechanism of optical-generated carriers. This research not only theoretically and experimentally proves the piezo-phototronic effect modulated the quantum photovoltaic device but also provides a great promise to maximize the use of solar energy in the current energy revolution. Influence of Thermal Annealing on Free Carrier Concentration in (GaN)1-x(ZnO)x Semiconductors Department of Chemistry, Stony Brook University, Stony Brook, NY, 11794, USA Department of Geosciences, Stony Brook University, Stony Brook, NY, 11794, USA Department of Chemistry, University of Massachusetts Amherst, 710 N Pleasant St, Amherst, MA 01003, USA Chemistry Division, Brookhaven National Laboratories, Upton, New York, 11793, USA

Center for Functional Nanomaterials, Brookhaven National Laboratories, Upton, New York, 11793, USA J. Phys. Chem. C http://dx.doi.org/10.1021/acs.jpcc.7b06455

It was previously demonstrated that the efficiency of (GaN)1−x(ZnO)x semiconductors for solar water splitting can be improved by thermal annealing, though the origin of this improvement was not resolved. In the present work, it is shown that annealing reduces the free carrier (electron) concentration of (GaN)1−x(ZnO)x. The time-, temperature-, and atmosphere-dependent changes were followed through two simple techniques: indirect diffuse reflectance measurements from 0.5 – 3.0 eV which show very high sensitivity to the free carrier response at the lowest energies, and EPR measurements which directly probe the number of unpaired electrons. For the thermal annealing of investigated compositions, it is found that temperatures of 250 °C and below do not measurably change the free carrier concentration, a gradual reduction of the free carrier concentration occurs over a time period of many hours at 350 °C and the complete elimination of free carriers happens within an hour at 550 °C. These changes are driven by an oxidative process which is effectively supressed under actively reducing atmospheres (H2, NH3), but which can still occur under nominally inert gases (N2, Ar). Surprisingly, it is found that the N2 gas released during thermal oxidation of (GaN)1−x(ZnO)x samples remains trapped within the solid matrix and is not expelled until temperatures of about 900 °C, a result directly confirmed through neutron pair-distribution fuction (PDF) measurements which show a new peak at the 1.1 Å bond length of molecular nitrogen after annealing. Preliminary comparative photoelectrochemical (PEC) measurements of the influence of free carrier concentration on photoactivity for water oxidation were carried out for a sample with x = 0.64. Samples annealed to eliminate free carriers exhibited no photoactivity for water oxidation, while a complex dependence on carrier concentration was observed for samples with intermediate free carrier concentrations. The methods demonstrated here provide an important

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approach for quantifying (and controlling) the carrier concentrations of semiconductors which are only available in the form of loose powders, as is commonly the case for oxynitride compounds. Research on quantum efficiency and photoemission characteristics of exponential-doping GaN nanowire photocathode Department of Optoelectronic Technology, School of Electronic and Optical Engineering, Nanjing University of Science and Technology, Nanjing, China Journal of Materials Science https://doi.org/10.1007/s10853-017-1394-x

Aimed at improving the actual photoemission performance of nanowire photocathode, an axial exponential-doping GaN nanowire photocathode is proposed. Based on two-dimensional continuity equation and finite difference method, the quantum efficiency of this exponential-doping GaN nanowire photocathode is obtained. The simulation results suggest that this structure of GaN nanowire photocathode can effectively obviate the difficulty in collecting the electrons escaping from side faces because a large part of carriers will escape from top surface under the built-in electric field. Besides, it is discovered that the optimal height of nanowires is 300 nm when the doping concentration of top surface is 1 × 1018 cm−3 and that of back interface is 1 × 1019 cm−3. Then, when the nanowires are arranged as array, the optimal light angle of incidence is approximately 60° by analyzing the electrons flow density of the array. By comparison of collection proportion of photoelectrons, the optimal nanowire spacing is 231 nm. This study demonstrates potential application value of exponential-doping GaN nanowire photocathode. The results can direct the preparation of this kind of photocathode. Effect of metal-fingers/doped-ZnO transparent electrode on performance of GaN/InGaN solar cell Microelectronics and VLSI Design Group, Department of Electronics and Communication Engineering, National Institute of Technology Silchar, Assam, 788010, India Journal of Semiconductors https://doi.org/10.1088/1674-4926/38/9/092001

The effect of doped-ZnO transparent conductive oxide (TCO) with metal (Ag)-fingers contact on GaN/InGaN solar cell is investigated through numerical simulations. An optical and electrical

analysis of different dopant elements (such as B, Al, Ga, In and Sn) with ZnO as a top TCO layer is studied. A comparative analysis of metal square pad electrode, metal grid pattern electrode and metal-finger/ZnO type electrodes are taken into consideration to ensure the effect of anti-reflectivity by ZnO. The effect of thickness of ZnO and i-InGaN layer on performance of solar cell is also studied in detail. The proposed solar cell structure with Ag-fingers/ZnO:Al as top contact electrode shows interesting device characteristics compared to other dopants and metal top electrodes. The device achieves open circuit voltage ~2.525 V, short circuit current ~4.256 mA/cm2, fill factor ~87.86% and efficiency ~9.22% under 1 Sun, air mass 1.5 global illumination. Photoelectrochemical hydrogen generation from water using undoped GaN with selective-area Si-implanted stripes as photoelectrodes Jinn-Kong Sheu et al. J. Mater. Chem. A http://dx.doi.org/10.1039/C7TA07155H

This study examines photoelectrochemical (PEC) cells with undoped GaN (u-GaN) photoelectrodes that feature selective-area Si implantation stripes for hydrogen (H2) generation using NaCl solution as electrolyte. Selective-area Si implantation was performed on the u-GaN layer to create n+-GaN stripes with higher carrier concentration than the u-GaN area. Si-implanted n+-GaN stripes behave like metal lines, but they allow light to penetrate Si-implanted regions, to facilitate the collection of photogenerated carriers. For a moderate area ratio of Si implantation, the typical hydrogen generation rate of u-GaN working electrodes with and without Si-implanted GaN stripes were approximately 98

mole/hr cm2 and 68 mole/hr cm2, respectively, when the applied potential was 1 V. These values correspond to an enhanced H2 generation rate of around 44%. The marked enhancement in hydrogen generation rate is attributed to the fact that photogenerated electrons can be effectively collected by Si-implanted n+-GaN stripes. Microscopy showed an insignificant change in Si-implanted surfaces before and after PEC reaction. By contrast, u-GaN area without Si implantation exhibited significant corrosion after PEC reaction. The findings of this study indicate that the u-GaN epitaxial layer with Si-

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implanted stripes can be potentially used as robust photoelectrodes to efficiently generate hydrogen. Novel heterostructured InN/TiO2 submicron fibers designed for high performance visible-light-driven photocatalysis Zhen Su et al. Catal. Sci. Technol. http://dx.doi.org/10.1039/C7CY01207A

As a typical photocatalyst, TiO2 can only absorb the UV light limited by its wide band gap, which severely limits its industry application. Seeking for effective strategies to enable its visible light absorption is on the spotlight. In this paper, InN with a band gap of 0.7 eV was incorporated into TiO2 nanofiber to obtain high-performance visible-light photocatalyst for the first time. Heterostructured InN/TiO2 submicron fibers were facilely fabricated via electrospining technique followed by nitridation procedure. InN was homogeneously distributed in the TiO2 matrix, as characterized by transmission electron microscope. Owing to the ultra-narrow band gap of InN, the light absorption of the InN/TiO2 hybrid submicron fibers was broadened to visible wavelengths. The photocatalytic performance of the heterostructure was assessed by the decomposition of rhodamine B under visible light irradiation. Approximately 80% rhodamine B was decomposed in just 15 min. The rate constant reached up to 0.089 min−1, which was enhanced by 45 times compared with electrospun TiO2 fibers. This great improvement of photocatalytic property was attributed to both the intense visible-light absorption and efficient charge separation enabled by the homogeneous distribution of InN phase in TiO2 fibers. The photocatalytic efficiency achieved here was among the highest values of the currently reported photocatalysts. The results obtained in this work may pave a new way for the fabrication of high-performance visible-light photocatalysts.

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GROUP 7 - Materials, Technology and Fundamental Group leader: Jean-Christophe Harmand (LPN-CNRS)

NANO

Information selected by Jesús Zúñiga Pérez (CRHEA-CNRS)

Molecular beam epitaxial growth and characterization of AlN nanowall deep UV light emitting diodes Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, Michigan 48109, USA Department of Electrical and Computer Engineering, McGill University, 3480 University Street, Montreal, Quebec H3A 0E9, Canada Appl. Phys. Lett. http://dx.doi.org/10.1063/1.4989551

We have demonstrated large area AlN nanowall light emitting diodes grown on a sapphire substrate, which operate at 214 nm. Through detailed temperature-dependent and power-dependent photoluminescence measurements and rate equation analysis, a relatively high internal quantum efficiency (∼60%) was derived for AlN nanowall structures at room-temperature. A consistent blueshift in the emission wavelengths was measured with decreasing nanowall widths due to the reduced tensile strain distribution. The devices exhibit excellent current-voltage characteristics, including a turn-on voltage of 7 V and current densities of  >170 A/cm2 at 12 V. Near-Infrared Intersubband Photodetection in GaN/AlN Nanowires Université Grenoble-Alpes, CEA, INAC, PHELIQS, 17 av. des Martyrs, 38000 Grenoble, France Université Grenoble-Alpes, CNRS, Institut Néel, 25 av. des Martyrs, 38000 Grenoble, France Nano Lett. http://dx.doi.org/10.1021/acs.nanolett.7b03414

Intersubband optoelectronic devices rely on transitions between quantum-confined electron levels in semiconductor heterostructures, which enables infrared (IR) photodetection in the 1–30 μm wavelength window with picosecond response times. Incorporating nanowires as active media could enable an independent control over the

electrical cross-section of the device and the optical absorption cross-section. Furthermore, the three-dimensional carrier confinement in nanowire heterostructures opens new possibilities to tune the carrier relaxation time. However, the generation of structural defects and the surface sensitivity of GaAs nanowires have so far hindered the fabrication of nanowire intersubband devices. Here, we report the first demonstration of intersubband photodetection in a nanowire, using GaN nanowires containing a GaN/AlN superlattice absorbing at 1.55 μm. The combination of spectral photocurrent measurements with 8-band k·p calculations of the electronic structure supports the interpretation of the result as intersubband photodetection in these extremely short-period superlattices. We observe a linear dependence of the photocurrent with the incident illumination power, which confirms the insensitivity of the intersubband process to surface states and highlights how architectures featuring large surface-to-volume ratios are suitable as intersubband photodetectors. Our analysis of the photocurrent characteristics points out routes for an improvement of the device performance. This first nanowire based intersubband photodetector represents a technological breakthrough that paves the way to a powerful device platform with potential for ultrafast, ultrasensitive photodetectors and highly efficient quantum cascade emitters with improved thermal stability. Ultraviolet-C Photodetector Fabricated Using Si-Doped n-AlGaN Nanorods Grown by MOCVD Semiconductor Materials Process Laboratory, School of Advanced Materials Engineering, Engineering College, Research Center for Advanced Materials Development (RCAMD), Chonbuk National University, Baekje-daero 567, Jeonju 54896, Republic of Korea ACS Photonics http://dx.doi.org/10.1021/acsphotonics.7b01047

Aluminum gallium nitride (AlxGa1–xN) alloy films and nanostructures have attracted extensive research attention for ultraviolet (UV) and deep ultraviolet optoelectronic applications. However, the morphology-controlled growth of high-quality

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AlxGa1–xN quasi one-dimensional nanostructures has been limited by the complex multicomponent phase diagram and inhomogeneous composition distribution. Here, we demonstrated the growth of Si-doped n-type compositionally uniform Al0.45Ga0.55N nanorods employing a metal organic chemical vapor deposition (MOCVD) technique for the application in UV-C photodetectors. A two-step growth process, namely, growth of undoped GaN seeds and subsequent growth of n-AlGaN nanorods over GaN seeds, has been developed. Various characterization techniques have been used to study the crystalline quality, orientation, and optical properties of the realized nanorods. Field emission scanning electron microscopy revealed a uniform distribution of vertically aligned n-AlGaN nanorods over the GaN seeds. X-ray diffraction studies showed that the grown nanorods are preferentially (0002) oriented with hexagonal crystal structure. High-resolution transmission electron microscopy images indicated the nanorods are single crystalline in nature, without any significant crystalline defects and dislocations. Cathodoluminescence spectra of AlGaN nanorods displayed a strong band edge excitonic emission peak at 276 nm at 77 K and shifted to lower energy as the temperature increased to 300 K. The photocurrent current (Ip) of the fabricated photoconductive device was significantly higher in the UV region (250–276 nm) compared to the corresponding dark current. The photocurrent displayed a nonlinear power density (P)-dependent characteristics (Ip ∝ P0.64). The photoresponsivity and sensitivity of the fabricated photodetector were estimated to be ∼115 mA/W and ∼64%, respectively, in the UV-C region. Fabrication of Phosphor-Free III-Nitride Nanowire Light-Emitting Diodes on Metal Substrates for Flexible Photonics Department of Electrical and Computer Engineering and ⊥Electronic Imaging Center, New Jersey Institute of Technology, 323 Martin Luther King Boulevard, University Heights, Newark, New Jersey 07102, United States Epitaxial Laboratory Inc., Tiana Place, Dix Hills, New York 11746, United States Vietnam Academy of Science and Technology, Institute of Applied Materials Science, 1 Mac Dinh Chi Street, District 1, Ho Chi Minh City 70001, Vietnam Faculty of Science and Technology, Hoa Sen University, 8 Nguyen Van Trang Street, District 1, Ho Chi Minh City 70001, Vietnam

ACS Omega http://dx.doi.org/10.1021/acsomega.7b00843

In this paper, we report our study on high-performance III-nitride nanowire light-emitting diodes (LEDs) on copper (Cu) substrates via the substrate-transfer process. Nanowire LED structures were first grown on silicon-on-insulator (SOI) substrates by molecular beam epitaxy. Subsequently, the SOI substrate was removed by combining dry- and wet-etching processes. Compared to conventional nanowire LEDs on Si, the nanowire LEDs on Cu exhibit several advantages, including more efficient thermal management and enhanced light-extraction efficiency (LEE) because of the usage of metal reflectors and highly thermally conductive metal substrates. The LED on Cu, therefore, has stronger photoluminescence, electroluminescence intensities, and better current–voltage characteristics compared to the conventional nanowire LED on Si. Our simulation results further confirm the improved device performance of LEDs on Cu, compared to LEDs on Si. The LEE of the nanowire LED on Cu is nine times higher than that of the LED on Si at the same nanowire radius of 60 nm and spacing of 130 nm. Moreover, by engineering the device-active region, we achieved high-brightness phosphor-free LEDs on Cu with highly stable white-light emission and high color-rendering index of ∼95, showing their promising applications in general lighting, flexible displays, and wearable applications. Collective Lasing Behavior of Monolithic GaN–InGaN Core–Shell Nanorod Lattice under Room Temperature Department of Photonics and Institute of Electro-Optical Engineering, National Chiao Tung University, 1001 Ta Hsueh Road, Hsinchu 300, Taiwan Nano Lett. http://dx.doi.org/10.1021/acs.nanolett.7b02922

We demonstrated a monolithic GaN–InGaN core–shell nanorod lattice lasing under room temperature. The threshold pumping density was as low as 140 kW/cm2 with a quality factor as high as 1940. The narrow mode spacing between lasing peaks suggested a strong coupling between adjacent whisper gallery modes (WGM), which was confirmed with the far-field patterns. Excitation area dependent photoluminescence revealed that the long-wavelength lasing modes dominated the

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collective lasing behavior under a large excitation area. The excitation-area-dependent lasing behavior resulted from the prominent optical coupling among rods. According to the optical mode simulations and truncated-rod experiments, we confirmed that the fine-splitting of lasing peaks originated from the coupled supermodes existing in the periodic nanorod lattices. With wavelength-tunable active materials and a wafer-level scalable processing, patterning optically coupled GaN–InGaN core–shell nanorods is a highly practical approach for building various on-chip optical components including emitters and coupled resonator waveguides in visible and ultraviolet spectral range. GaN Metalens for Pixel-Level Full-Color Routing at Visible Light Department of Physics, National Taiwan University, Taipei 10617, Taiwan Research Center for Applied Sciences, Academia Sinica, Taipei 11529, Taiwan Department of Electrical Engineering, National United University, Miaoli 36063, Taiwan Department of Photonics, National Cheng Kung University, Tainan 70101, Taiwan Department of Electrical Engineering and Graduate Institute of Electronics Engineering, National Taiwan University, Taipei 10617, Taiwan College of Engineering, Chang Gung University, Taoyuan 33302, Taiwan Nano Lett. http://dx.doi.org/10.1021/acs.nanolett.7b03135

Metasurface-based components are known to be one of the promising candidates for developing flat optical systems. However, their low working efficiency highly limits the use of such flat components for feasible applications. Although the introduction of the metallic mirror has been demonstrated to successfully enhance the efficiency, it is still somehow limited for imaging and sensing applications because they are only available for devices operating in a reflection fashion. Here, we demonstrate three individual GaN-based metalenses working in a transmission window with extremely high operation efficiency at visible light (87%, 91.6%, and 50.6% for blue, green, and red light, respectively). For the proof of concept, a multiplex color router with dielectric metalens, which is capable of guiding individual primary colors into different spatial positions, is experimentally verified based on the design of out-

of-plane focusing metalens. Our approach with low-cost, semiconductor fabrication compatibility and high working efficiency characteristics offers a way for establishing a complete set of flat optical components for a wide range of applications such as compact imaging sensors, optical spectroscopy, and high-resolution lithography, just named a few. Effect of surface roughness, chemical composition, and native oxide crystallinity on the orientation of self-assembled GaN nanowires on Ti foils Paul-Drude-Institut für Festkörperelektronik, Leibniz-Institut im Forschungsverbund Berlin e.V., Hausvogteiplatz 5–7, 10117 Berlin, Germany Department of Electronic Systems, NTNU Norwegian University of Science and Technology, Trondheim NO-7491, Norway Nanotechnology https://doi.org/10.1088/1361-6528/aa84a1

We report on plasma-assisted molecular beam epitaxial growth of almost randomly oriented, uniformly tilted, and vertically aligned self-assembled GaN nanowires (NWs), respectively, on different types of polycrystalline Ti foils. The NW orientation with respect to the substrate normal, which is affected by an in situ treatment of the foil surface before NW growth, depends on the crystallinity of the native oxide. Direct growth on the as-received foils results in the formation of ensembles of nearly randomly oriented NWs due to the strong roughening of the surface induced by chemical reactions between the impinging elements and Ti. Surface nitridation preceding the NW growth is found to reduce this roughening by transformation of the uppermost layers into TiN and TiO x N y species. These compounds are more stable against chemical reactions and facilitate the growth of uniformly oriented GaN NW ensembles on the surface of the individual grains of the polycrystalline Ti foils. If an amorphous oxide layer is present at the foil surface, vertically oriented NWs are obtained all across the substrate because this layer blocks the transfering of the epitaxial information from the underlying grains. The control of NW orientation and the understanding behind the achievement of vertically oriented NWs obtained in this study represent an important step towards the realization of GaN NW-based bendable devices on polycrystalline metal foils.

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Effect of doping on the intersubband absorption in Si- and Ge-doped GaN/AlN heterostructures Université Grenoble-Alpes, F-38000 Grenoble, France CEA-Grenoble, INAC-PHELIQS, 17 av. des Martyrs, F-38000 Grenoble, France CNRS-Institute Néel, 25 av. des Martyrs, F-38000 Grenoble, France Nanotechnology https://doi.org/10.1088/1361-6528/aa8504

In this paper, we study band-to-band and intersubband (ISB) characteristics of Si- and Ge-doped GaN/AlN heterostructures (planar and nanowires) structurally designed to absorb in the short-wavelength infrared region, particularly at 1.55 μm. Regarding the band-to-band properties, we discuss the variation of the screening of the internal electric field by free carriers, as a function of the doping density and well/nanodisk size. We observe that nanowire heterostructures consistently present longer photoluminescence decay times than their planar counterparts, which supports the existence of an in-plane piezoelectric field associated to the shear component of the strain tensor in the nanowire geometry. Regarding the ISB characteristics, we report absorption covering 1.45–1.75 μm using Ge-doped quantum wells, with comparable performance to Si-doped planar heterostructures. We also report similar ISB absorption in Si- and Ge-doped nanowire heterostructures indicating that the choice of dopant is not an intrinsic barrier for observing ISB phenomena. The spectral shift of the ISB absorption as a function of the doping concentration due to many body effects confirms that Si and Ge efficiently dope GaN/AlN nanowire heterostructures. Fabrication of AlGaN nanorods with different Al compositions for emission enhancement in UV range Jiangsu Provincial Key Laboratory of Advanced Photonic and Electronic Materials, School of Electronic Science and Engineering, Nanjing University, Nanjing 210093, People's Republic of China Nanjing National Laboratory of Microstructures, Nanjing University, Nanjing 210093, People's Republic of China College of Engineering and Applied Sciences, Nanjing University, Nanjing 210093, People's Republic of China Nanotechnology https://doi.org/10.1088/1361-6528/aa7ba4

Highly ordered AlxGa1−xN nanorods with varied aluminum alloy compositions (0.18 ≤ x ≤ 0.8) are fabricated with nanoimprint lithography and top-down dry etching techniques. And the structural properties and morphology are obtained by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Compared with as-grown AlGaN samples, nanorod samples reveal outstanding optical performance on account of strain releasing and light extraction enhancement. Through Raman scattering and cathodeluminescence measurements, it has been observed clear red-shifts of E2h modes and near band edge emission (NBE) peaks of AlGaN nanorods compared to the planar ones, indicating the residual strain releasing after nano-fabrication. The integrated intensities of NBE peaks of AlGaN nanorods manifest light emission enhancement up to 2.7 at deep-UV range. Finite-difference time-domain (FDTD) simulations have been adopted to investigate the light extraction and far-field distribution of such structures, it turned out that ordered nanorod array can enhance the TM polarized emission extraction 2–7 folds compared to the planar structure. The optical regulation in nanorod arrays should take the responsibility for the observed optical enhancements, which is proved by the far-field distribution of light, thus it can improve the performance of ultraviolet LEDs.

NON/SEMI POLAR Information selected by

Philippe De Mierry (CRHEA-CNRS) Efficient semipolar (11-22) 550 nm yellow/green InGaN light-emitting diodes on low defect density (11-22) GaN/sapphire templates Materials Department, University of California, Santa Barbara, California 93106, USA Department of Electrical and Computer Engineering, University of California, Santa Barbara, California 93117, USA CNRS - CRHEA, Rue Bernard Grégory, 06560 Valbonne, France Institute of Nano Optoelectronics Research and Technology, Universiti Sains Malaysia, 11800 USM, Penang, Malaysia ACS Appl. Mater. Interfaces http://dx.doi.org/10.1021/acsami.7b11718

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We demonstrate efficient semipolar (11-22) 550 nm yellow/green InGaN light-emitting diodes (LEDs) with In0.03Ga0.97N barriers on low defect density (11-22) GaN/patterned sapphire templates. The In0.03Ga0.97N barriers were clearly identified and no InGaN clusters were observed by atom probe tomography (APT) measurements. The semipolar (11-22) 550 nm InGaN LEDs (0.1 mm2 size) show an output power of 2.4 mW at 100 mA and a peak external quantum efficiency (EQE) of 1.3% with a low efficiency droop. In addition, the LEDs exhibit a small blue-shift of only 11 nm as injection current increases from 5 to 100 mA. These results suggest the potential to produce high efficiency semipolar InGaN LEDs with long emission wavelength on large-area sapphire substrates with economical feasibility. 444 nm InGaN light emitting diodes on low-defect-density (11-22) GaN templates on patterned sapphire Materials Department, University of California, Santa Barbara, CA 93106, U.S.A. Department of Electrical and Computer Engineering, University of California, Santa Barbara, CA 93117, U.S.A. Université Côte d'Azur, CNRS–CRHEA, 06560 Valbonne, France Applied Physics Express https://doi.org/10.7567/APEX.10.106501

Efficient InGaN-based 444 nm blue light-emitting diodes (LEDs) were fabricated on low-defect-density (11-22) semipolar GaN templates grown on patterned r-sapphire. At 20 A/cm2, the packaged (11-22) LEDs exhibited a light output power of 2.9 mW (17.8 mW at 100 A/cm2) and a record peak external quantum efficiency of 6.4% showing a negligible efficiency droop and blue shift with drive currents up to 100 A/cm2. In addition, we demonstrated light extraction simulations for the (11-22) template, which showed that the structured pattern is not only beneficial for limiting the defect propagation but also increases the light extraction by 29% compared with GaN layers grown on planar substrates.

MATERIAL / CHARACTERIZATION / EQUIPMENT / NUMERICAL SIMULATION

Information selected by Agnès Trassoudaine (Université d'Auvergne)

and Yvon Cordier (CRHEA-CNRS)

Epitaxial ScAlN Etch-Stop Layers Grown by Molecular Beam Epitaxy for Selective Etching of AlN and GaN U.S. Naval Research Laboratory, Washington, DC 20375 USA IEEE Transactions on Semiconductor Manufacturing https://doi.org/10.1109/TSM.2017.2749201

Although selective dry etches exist for GaN, it is difficult to selectively etch AlN in heterostructures with other conventional III-N epitaxial materials. The reduction in etch rate resulting from the addition of 2-16% scandium to ScxAl₁-xN in conventional Cl₂/BCl₃/Ar inductively coupled plasma etching is presented. Smooth, epitaxial ScxAl₁-xN layers are grown by RF-plasma-assisted molecular beam epitaxy directly on 4H-SiC substrates. The etch selectivity with respect to AlN is as high as 10.6 and 11.2 for x = 0.02 and 0.16, respectively, allowing ScxAl₁-xN to act as an etch-stop layer with minimal misfit strain when grown within either AlN or GaN based heterostructures. DFT modeling of carbon incorporation in GaN(0001) and GaN(000-1) metalorganic vapor phase epitaxy Center for Integrated Research of Future Electronics, Institute of Materials and Systems for Sustainability, Nagoya University, Nagoya 464-8603, Japan Institute of High Pressure Physics, Polish Academy of Sciences, Sokolowska 29/37, 01-142 Warsaw, Poland Research Institute for Applied Mechanics, Kyushu University, Kasuga, Fukuoka 816-8580, Japan Department of Aeronautics and Astronautics, Kyushu University, Nishi-ku, Fukuoka 819-0395, Japan Appl. Phys. Lett. http://dx.doi.org/10.1063/1.4991608

The carbon incorporation mechanism in GaN(0001) and GaN(000-1) during MOVPE was investigated using density functional theory (DFT) calculations. The results confirm that the crucial factors for carbon incorporation are Fermi level pinning and accompanying surface band bending. In addition, the lattice symmetry has a strong dependence on the stability of carbon in a few subsurface layers,

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which results from interactions between the impurities and surface states. It was shown that these effects are responsible for facilitating or hindering the incorporation of impurities and dopants. The influence of diluent gas species (hydrogen or nitrogen) on carbon incorporation was discussed. Growth of AlGaN under the conditions of significant gallium evaporation: Phase separation and enhanced lateral growth National Research Centre “Kurchatov institute,” Moscow 123182, Russia Journal of Applied Physics http://dx.doi.org/10.1063/1.5002070

The growth kinetics of AlGaN in NH3 MBE under significant Ga desorption was studied. It was found that the addition of gallium stimulates 2D growth and provides better morphology of films compared to pure AlN. The effect was experimentally observed at up to 98% desorption of the impinging gallium. We found that under the conditions of significant thermal desorption, larger amounts of gallium were retained at lateral boundaries of 3D surface features than at flat terraces because of the higher binding energy of Ga atoms at specific surface defects. The selective accumulation of gallium resulted in an increase in the lateral growth component through the formation of the Ga-enriched AlGaN phase at boundaries of 3D surface features. We studied the temperature dependence of AlGaN growth rate and developed a kinetic model analytically describing this dependence. As the model was in good agreement with the experimental data, we used it to estimate the increase in the binding energy of Ga atoms at surface defects compared to terrace surface sites using data on the Ga content in different AlGaN phases. We also applied first-principles calculations to the thermodynamic analysis of stable configurations on the AlN surface and then used these surface configurations to compare the binding energy of Ga atoms at terraces and steps. Both first-principles calculations and analytical estimations of the experimental results gave similar values of difference in binding energies; this value is 0.3 eV. Finally, it was studied experimentally whether gallium can act as a surfactant in AlN growth by NH3 MBE at elevated temperatures. Gallium application has allowed us to grow a

300 nm thick AlN film with a RMS surface roughness of 2.2 Å over an area of 10 ×× 10 μm and a reduced density of screw dislocations. Threading dislocation reduction in three-dimensionally grown GaN islands on Si (111) substrate with AlN/AlGaN buffer layers Department of Materials Science and Engineering, National Chiao Tung University, University Rd. 1001, Hsinchu 30010, Taiwan Journal of Applied Physics http://dx.doi.org/10.1063/1.5002079

Three-dimensional GaN island growth without any masks was first introduced under high pressure in metalorganic chemical vapor deposition after the growth of AlN and AlGaN buffer layers on Si (111) substrate, followed by two-dimensional GaN growth to form a continuous GaN film with improvement of the crystalline quality and surface smoothness. X-ray diffraction and cross-sectional scanning transmission electron microscopy analyses show that a high-quality GaN film can be achieved by bending of edge threading dislocations (TDs) and the formation of dislocation half-loops. It is observed that most of edge TDs bend 90° from the growth direction along c-axis, whereas mixed TDs bend about 30° towards the inclined sidewall facets of the islands. Consequently, a 1.2 μm thick GaN epitaxial film with a low threading dislocation density of 2.5 × 108 cm−2 and a smooth surface of 0. 38 nm roughness can be achieved on Si substrate. In-situ TEM study of domain switching in GaN thin films Department of Mechanical and Nuclear Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, USA Pen-Tung Sah Institute of Micro-Nano Science and Technology, Xiamen University, Xiamen 361005, People's Republic of China Air Force Research Laboratory, 2941 Hobson Way, Wright-Patterson AFB, Ohio 45433, USA Appl. Phys. Lett. http://dx.doi.org/10.1063/1.5002690

Microstructural response of gallium nitride (GaN) films, grown by metal-organic chemical vapor deposition, was studied as a function of applied electrical field. In-situ transmission electron microscopy showed sudden change in the electron

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diffraction pattern reflecting domain switching at around 20 V bias, applied perpendicular to the polarization direction. No such switching was observed for thicker films or for the field applied along the polarization direction. This anomalous behavior is explained by the nanoscale size effects on the piezoelectric coefficients of GaN, which can be 2–3 times larger than the bulk value. As a result, a large amount of internal energy can be imparted in 100 nm thick films to induce domain switching at relatively lower voltages to induce such events at the bulk scale. Evolution of threading dislocations in GaN epitaxial laterally overgrown on GaN templates using self-organized graphene as a nano-mask Suzhou Institute of Nano-Tech and Nano-Bionics (SINANO), Chinese Academy of Sciences (CAS), Suzhou 215123, People's Republic of China Suzhou Nanowin Science and Technology Co., Ltd., Suzhou 215123, People's Republic of China University of Chinese Academy of Sciences, Beijing 100049, People's Republic of China College of Physics, Optoelectronics and Energy and Collaborative Innovation Center of Suzhou Nano Science and Technology, Soochow University, Suzhou 215006, People's Republic of China Key Lab of Advanced Optical Manufacturing Technologies of Jiangsu Province and Key Lab of Modern Optical Technologies of Education Ministry of China, Soochow University, Suzhou 215006, People's Republic of China Appl. Phys. Lett. http://dx.doi.org/10.1063/1.4998924

Growth of high-quality GaN within a limited thickness is still a challenge, which is important both in improving device performance and in reducing the cost. In this work, a self-organized graphene is investigated as a nano-mask for two-step GaN epitaxial lateral overgrowth (2S-ELOG) in hydride vapor phase epitaxy. Efficient improvement of crystal quality was revealed by x-ray diffraction. The microstructural properties, especially the evolution of threading dislocations (TDs), were investigated by scanning electron microscopy and transmission electron microscopy. Stacking faults blocked the propagation of TDs, and fewer new TDs were subsequently generated by the coalescence of different orientational domains and lateral-overgrown GaN. This evolution mechanism of TDs was different from that of traditional ELOG

technology or one-step ELOG (1S-ELOG) technology using a two-dimensional (2D) material as a mask. Step-free GaN surfaces grown by confined-area metal-organic vapor phase epitaxy North Carolina State University, Raleigh, North Carolina 27607, USA Sandia National Laboratories, Albuquerque, New Mexico 87185, USA Center for Nanophase Materials Science, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA APL Materials http://dx.doi.org/10.1063/1.4993840

A two-step homoepitaxial growth process producing step-free surfaces on low dislocation density, Ga-polar ammonothermal GaN single crystals is described. Growth is conducted under very low supersaturation conditions where adatom incorporation occurs predominantly at step edges, and lateral growth is strongly preferred. The achievable step-free area is limited by the substrate dislocation density. For ammonothermal crystals with an average dislocation density of ∼1 × 104 cm−2, step-free mesas up to 200 × 200 μm2 in size are achieved. These remarkable surfaces create a unique opportunity to study the effect of steps on the properties and performance of semiconductor heterostructures. XeF2 etching of epitaxial Nb2N for lift-off or micromachining of III-N materials and devices US Naval Research Laboratory, Electronics Science and Technology Division, 4555 Overlook Ave. SW, Washington, DC 20375, USA Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films http://dx.doi.org/10.1116/1.4994400

This paper presents characterization of the effects of XeF2 vapor phase etching conditions on the lateral etch rate and etch uniformity of a sacrificial, epitaxial Nb2N layer grown between a III-N high-electron-mobility transistor heterostructure and a 6H-SiC substrate. To achieve uniform and repeatable lateral Nb2N removal, an etch temperature of 100 °C or higher was required, providing average etch rates ranging from 10 to 40 μm/min. A net compressive stress and positive strain gradient in the released III-N material were inferred from the buckling of clamped-clamped

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beams and the convex curvature of cantilever structures, respectively. XeF2 etching of epitaxial Nb2N sacrificial layers in III-N material structures allows for a highly selective, completely dry release process that is compatible with common micromachining and epitaxial lift-off techniques. In situ stress measurements during MOCVD growth of thick N-polar InGaN Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, USA Materials Research Institute, The Pennsylvania State University, University Park, Pennsylvania 16802, USA Journal of Applied Physics http://dx.doi.org/10.1063/1.4998745

The growth of N-polar InGaN films by metalorganic chemical vapor deposition (MOCVD) on N-polar GaN was investigated in order to understand the evolution of growth stress and the dislocation microstructure of relatively thick InGaN films (140 nm) in the absence of hexagonal hillocks and V-pits, which are typically present in III-polar InGaN. During in situ stress measurements of N-polar InGaN, growth initiates under an initial low stress state, which gradually transitions to a constant compressive incremental stress for the remainder of the film thickness. This behavior in the growth stress evolution in N-polar InGaN occurs regardless of the stress state of the GaN base layer (i.e., compression or tension), which was controlled by varying the temperature of the initial low temperature layer in a two-step temperature growth process for N-polar GaN. A blue shift in the PL peak emission of N-polar InGaN was, however, observed with increasing incremental compressive stress in the N-polar GaN base layer. These results provide insight into potential mechanisms of plastic relaxation in high crystal quality thick N-polar InGaN films grown by MOCVD. Photo-assisted Kelvin probe force microscopy investigation of three dimensional GaN structures with various crystal facets, doping types, and wavelengths of illumination Institut für Halbleitertechnik and Laboratory for Emerging Nanometrology, Technische Universität Braunschweig, 38092 Braunschweig, Germany Epitaxy competence center ec2, Hans-Sommer-Straße 66, 38106 Braunschweig, Germany

Physikalisch-Technische Bundesanstalt (PTB), Bundesallee 100, 38116 Braunschweig, Germany Institute of Nanochemistry and Nanobiology, Shanghai University, Shanghai 200444, People's Republic of China Osram Opto Semiconductors GmbH, Leibnizstraße 4, 93055 Regensburg, Germany Journal of Applied Physics http://dx.doi.org/10.1063/1.5000137

Three dimensional GaN structures with different crystal facets and doping types have been investigated employing the surface photo-voltage (SPV) method to monitor illumination-induced surface charge behavior using Kelvin probe force microscopy. Various photon energies near and below the GaN bandgap were used to modify the generation of electron–hole pairs and their motion under the influence of the electric field near the GaN surface. Fast and slow processes for Ga-polar c-planes on both Si-doped n-type as well as Mg-doped p-type GaN truncated pyramid micro-structures were found and their origin is discussed. The immediate positive (for n-type) and negative (for p-type) SPV response dominates at band-to-band and near-bandgap excitation, while only the slow process is present at sub-bandgap excitation. The SPV behavior for the semi-polar facets of the p-type GaN truncated pyramids has a similar characteristic to that on its c-plane, which indicates that it has a comparable band bending and no strong influence of the polarity-induced charges is detectable. The SPV behavior of the non-polar m-facets of the Si-doped n-type part of a transferred GaN column is similar to that of a clean c-plane GaN surface during illumination. However, the SPV is smaller in magnitude, which is attributed to intrinsic surface states of m-plane surfaces and their influence on the band bending. The SPV behavior of the non-polar m-facet of the slightly Mg-doped part of this GaN column is found to behave differently. Compared to c- and r-facets of p-type surfaces of GaN-light–emitting diode micro-structures, the m-plane is more chemically stable. AlGaN/GaN High Electron Mobility Transistor Grown and Fabricated on ZrTi Metallic Alloy Buffer Layers Department of Chemical Engineering, University of Florida, Gainesville, Florida 32611, USA Department of Materials Science Engineering, University of Florida, Gainesville, Florida 32611, USA Tivra Corporation, Oakland, California 94606, USA

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Department of Physics, Arizona State University, Tempe, Arizona 85287, USA Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830, USA ECS J. Solid State Sci. Technol. http://dx.doi.org/10.1149/2.0161711jss

AlGaN/GaN high electron mobility transistors (HEMTs) were demonstrated for structures grown on ZrTi metallic alloy buffer layers, which provided lattice matching of the in-plane lattice parameter (“a-parameter”) to hexagonal GaN. The quality of the GaN buffer layer and HEMT structure were confirmed with X-ray 2θ and rocking scans as well as cross-section transmission electron microscopy (TEM) images. The X-ray 2θ scans showed full widths at half maximum (FWHM) of 0.06°, 0.05° and 0.08° for ZrTi alloy, GaN buffer layer, and the entire HEMT structure, respectively. TEM of the lower section of the HEMT structure containing the GaN buffer layer and the AlN/ZrTi/AlN stack on the Si substrate showed that it was important to grow AlN on the top of ZrTi prior to growing the GaN buffer layer. The estimated threading dislocation (TD) density in the GaN channel layer of the HEMT structure was in the 108 cm−2 range. Recent Advancement in Charge and Photo-Assisted Non-Contact Electrical Characterization of SiC, GaN, and AlGaN/GaN HEMT Semilab SDI Semilab USA ECS Trans. http://dx.doi.org/10.1149/08007.0261ecst

The charge-based corona-Kelvin noncontact metrology, originally developed for Si IC fabrication, has recently been extended to wide energy gap semiconductors. We discuss principles of this extension and key applications, namely: high precision dopant measurement on SiC and GaN; two-dimensional electron gas characterization in AlGaN/GaN HEMT structures; interface and dielectric characterization on epi-layers with SiO2, SiN and Al2O3; comprehensive interfacial instability characterization of oxidized SiC; and whole wafer mapping of defects with a charge-assisted surface voltage technique. This powerful set of measurements is performed without fabrication of any test structures or electrical contact. Corresponding commercial tools are currently being

introduced. Based on the historical example of silicon IC, we believe that this approach shall offer enhanced testing for research and for manufacturing process control with reduced cost and fast data feedback benefiting the wide-bandgap device technology. Thermal Evolution of Implantation Damages in Mg-Implanted GaN Layers Grown on Si Univ. Grenoble Alpes CEA, LETI INAC MEM ECS Trans. http://dx.doi.org/10.1149/08007.0131ecst

We report on the structural characterization of Mg-implanted and annealed GaN layer on Si (111). Anneals ranging from 400 °C to 1100 °C are performed on samples implanted with 1013 - 1015 at/cm² Mg doses. A comparative study of the evolution of the damage in these samples as a function of annealing temperatures and implanted doses is performed by using photoluminescence (PL) and X-Ray Diffraction (XRD). For low Mg dose, the induced strain, measured via XRD, can be relaxed at relatively low temperature, i.e. 500 °C, while a 1000 °C anneal is required for higher dose. PL characteristics bands of Mg implanted in GaN are evidenced. Comparison of XRD and PL results show that the strain correction and the increase of the PL signal are not simultaneous. The trend in the evolution of the PL bands indicates that a higher thermal treatment would allow a better optical activation of Mg. Optimized Process and Tool Design for GaN Chemical Mechanical Planarization Ozyegin University, Faculty of Engineering, Mechanical Engineering Department, Nisantepe Mevki, Cekmekoy, Istanbul 34794 Turkey ECS J. Solid State Sci. Technol. http://dx.doi.org/10.1149/2.0201711jss

In this paper, we present a systematic approach to the gallium nitride (GaN) chemical mechanical planarization (CMP) process through evaluating the effect of crystallographic orientation, slurry chemistry and process variables on the removal rate and surface quality responses. A new CMP process and a complementary tool set-up are introduced to enhance GaN material removal rates.

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The key process variables are studied to set them at an optimal level, while a new slurry feed methodology is introduced in addition to a new tool set up to enable high material removal rates and acceptable surface quality through close control of the process chemistry. It is shown that the optimized settings can significantly improve the material removal rates as compared to the literature findings while simultaneously enabling a more sustainable process and potential removal selectivity against silica. Growth and Characterization of Bulk HVPE-GaN. Pathway to Highly Conductive and Semi-Insulating GaN Substrates Institute of High Pressure Physics PAS ECS Meeting Abstracts http://ma.ecsdl.org/content/MA2017-02/29/1251.abstract?sid=5232db56-5ce0-489c-934d-730e54ca610f

Development of GaN-based optoelectronic and electronic devices is closely linked to ongoing work devoted to crystallizing bulk GaN. Hydride vapor phase epitaxy (HVPE) is the most popular method for obtaining commercial-grade substrates. Significant advantages of HVPE are high growth rate and high purity of new-grown GaN. Using ammonothermal GaN substrates of high crystallographic and structural quality as seeds enables growth of HVPE-GaN of the same high quality [1]. Without intentional doping the material has a very low concentration of impurities and n-type conductivity comes from silicon with concentration close to 1×1017 cm-3. Free carrier concentration is at the level of 3-5×1016 cm-3. Controllable doping of HVPE-GaN to prepare substrates of specific parameters is still a challenge. In this work influence of different dopants on optical and electrical properties of GaN is presented. Results showing highly conductive n-type HVPE-GaN doped with silicon and germanium and semi-insulating material doped with carbon and iron with manganese will be presented. Characterization of the crystals includes their structural (X-ray diffraction, defect selective etching), optical (Raman spectroscopy, photoluminescence) and electrical (Hall measurements, Capacitance–voltage profiling) properties. Concentrations of dopants will be

examined by Secondary Ion Mass Spectrometry (SIMS). Detailed characterization of the grown GaN:Si and GaN:Ge will be presented. The way of introducing precursors to the HVPE reactor and details of crystallization process will be demonstrated. A difference between concentration of Si, which is always higher, and free electron concentration is observed in GaN:Si. This suggests that part of Si donors is compensated by an acceptor state. The strong yellow luminescence (YL) peaks suggest that this acceptor is gallium vacancy (VGa) or its complexes. The assumption is in good agreement with theoretical calculations of energy of VGa formation decreasing for highly n-type material [2]. However, when we incorporate Ge into our HVPE-GaN we observe no YL in the PL spectra and there is no significant difference between concentration of Ge and the free carrier concentration. This is probably connected to lack of VGa in GaN:Ge. Uniformity, in terms of free carrier concentration, of GaN:Si and GaN:Ge on c-plane and m-plane of crystals will be studied. It will be shown that highly conductive n-type material can be used as substrates for building laser diodes on them. When C is introduced to HVPE-GaN, using CH4 as a precursor, a strong YL peak is observed in PL spectra of crystallized material. The crystals are highly resistive (>108 Ωcm) at room temperature. Hall measurements performed up to 1000 K showed p-type conductivity with hole concentration 4×1015 cm-3. Activation energy of ~1 eV was calculated from Arrhenius plot. This is an experimental confirmation of DFT calculations performed for C substituted for N [3]. It is also an explanation for strong yellow luminescence (YL) present in PL spectra for GaN:C in this case not related to VGa but to C. Gallium nitride crystals can also be grown using solid iron as a source of dopants. Then, no yellow luminescence and only weak near band edge luminescence are visible in the crystals. A sharp peak is observed at 1.3 eV. This was shown before as an intrinsic transition of Fe impurity in GaN [4]. The grown crystals are highly resistive at room temperature. High-temperature Hall effect measurements revealed n-type conductivity with activation energy equal to 1.8 eV. Secondary ion mass spectrometry indicated the presence of

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manganese in the samples. The concentration of manganese was always higher than concentration of iron in the doped GaN. Evaluation of Hvpe GaN Layers Grown on Ammonothermal GaN Substrates By Synchrotron X-Ray Topography Stony Brook University U.S. Naval Research Laboratory Institute of High Pressure Physics PAS ECS Meeting Abstracts http://ma.ecsdl.org/content/MA2017-02/31/1331.abstract?sid=5232db56-5ce0-489c-934d-730e54ca610f

For obtaining low defect density GaN substrates with controllable electronic properties for high performance electronic and optoelectronic devices, quasi-bulk growth by hydride vapour phase epitaxy (HVPE) on ammonothermal grown GaN substrates appears to be a feasible approach [1]. Synchrotron X-ray topography (white beam and monochromatic beam) has been employed to characterize dislocation configurations in such GaN substrates that were grown by HVPE on ammonothermal GaN substrate, and then slicing the substrate. Threading dislocations and basal plane dislocations (BPDs) are observed in these GaN substrates. Compared with GaN grown on sapphire and silicon carbide substrates [2], HVPE GaN on ammonothermal GaN [3] is obviously of higher crystalline quality with lower defect densities. Threading screw dislocation (TSD) density was measured to be about 880 cm-2 while threading edge dislocation (TED) density was about an order higher (~ 5824 cm-2). The distribution of BPDs which are induced by deformation, was found to be highly non-uniform with most regions of the wafer nearly BPD-free as well as high densities concentrated near one edge. Also, besides the surface features, like the surface scratches, arrays of threading dislocations can be seen from the transmission and grazing incidence topographs, which likely originate from scratches on the surface of the ammonothermal substrate. Correlation of the defect distributions with the HVPE growth process and their implication for devices will be discussed.

On Ni/Au Alloyed Contacts to Mg-Doped GaN Department of Materials Science and Engineering, North Carolina State University, Raleigh, USA Adroit Materials, Cary, USA Journal of Electronic Materials https://doi.org/10.1007/s11664-017-5775-3

Ni/Au contacts to p-GaN were studied as a function of free hole concentration in GaN using planar transmission line measurement structures. All contacts showed a nonlinear behavior, which became stronger for lower doping concentrations. Electrical and structural analysis indicated that the current conduction between the contact and the p-GaN was through localized nano-sized clusters. Thus, the non-linear contact behavior can be well explained using the alloyed contact model. Two contributions to the contact resistance were identified: the spreading resistance in the semiconductor developed by the current crowding around the electrically active clusters, and diode-type behavior at the interface of the electrically active clusters with the semiconductor. Hence, the equivalent Ni/Au contact model consists of a diode and a resistor in series for each active cluster. The reduced barrier height observed in the measurements is thought to be generated by the extraction of Ga from the crystalline surface and localized formation of the Au:Ga phase. The alloyed contact analyses presented in this work are in good agreement with some of the commonly observed behavior of similar contacts described in the literature. The residual C concentration control for low temperature growth p-type GaN State Key Laboratory on Integrated Optoelectronics, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China School of Electronic, Electrical and Communication Engineering, University of Chinese Academy of Sciences, Beijing 100049, China Suzhou Institute of Nano-tech and Nano-bionics, Chinese Academy of Sciences, Suzhou 215123, China Chinese Physics B https://doi.org/10.1088/1674-1056/26/10/107102

In this work, the influence of C concentration to the performance of low temperature growth p-GaN is studied. Through analyses, we have confirmed that the C impurity has a compensation effect to p-GaN.

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At the same time we have found that several growth and annealing parameters have influences on the residual C concentration: (i) the C concentration decreases with the increase of growth pressure; (ii) we have found there exists a Ga memory effect when changing the Cp2Mg flow which will lead the growth rate and C concentration increase along the increase of Cp2Mg flow; (iii) annealing outside of metal–organic chemical vapor deposition (MOCVD) could decrease the C concentration while in situ annealing in MOCVD has an immobilization role to C concentration. Halide vapor phase epitaxy of thick GaN films on ScAlMgO4 substrates and their self-separation for fabricating freestanding wafers Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan Nichia Corporation, Anan, Tokushima 774-8601, Japan Applied Physics Express https://doi.org/10.7567/APEX.10.101001

Halide vapor phase epitaxy of thick GaN films was demonstrated on ScAlMgO4 (SCAM) substrates, and their self-separation was achieved. The 320-µm-thick GaN film was self-separated from the SCAM substrate during the cooling process after the growth. This separation phenomenon occurred because of both the c-plane cleavability of SCAM and the difference in the thermal-expansion coefficients between GaN and SCAM. The dark-spot densities for the GaN films on the SCAM substrates were approximately 30% lower than those on sapphire substrates. These results indicate that SCAM substrates are promising for fabricating a high-quality freestanding GaN wafer at a low cost. Numerical simulations of the electrical transport characteristics of a Pt/n-GaN Schottky diode Laboratory of Metallic and Semiconductor Materials, University of Biskra, P. O. Box 145, Biskra 07000, Algeria Thin Films Development and Applications Unit UDCMA, Setif/Research Center in Industrial Technologies CRTI, P. O. Box 64, Cheraga 16014, Algeria DIIES-University of Reggio Calabria, Loc. Feo di Vito, Reggio Calabria I-89100, Italy Faculty of Science, University of Batna, Batna 05000, Algeria Japanese Journal of Applied Physics https://doi.org/10.7567/JJAP.56.094301

In this paper, using a numerical simulator, we investigated the current–voltage characteristics of a Pt/n-GaN thin Schottky diode on the basis of the thermionic emission (TE) theory in the 300 to 500 K temperature range. During the simulations, the effect of different defect states within the n-GaN bulk with different densities and spatial locations is considered. The results show that the diode ideality factor and the threshold voltage decrease with increasing temperature, while at the same time, the zero-bias Schottky barrier height (Φb0) extracted from the forward current density–voltage (J–V) characteristics increases. The observed behaviors of the ideality factor and zero-bias barrier height are analyzed on the basis of spatial barrier height inhomogeneities at the Pt/GaN interface by assuming a Gaussian distribution (GD). The plot of apparent barrier height (Φb,App) as a function of q/2kT gives a straight line, where the mean zero-bias barrier height ($\overline\Phi _\textb0$) and the standard deviation (σ0) are 1.48 eV and 0.047 V, respectively. The plot of the modified activation energy against q/kT gives an almost the same value of $\overline\Phi _\textb0$ and an effective Richardson constant A* of 28.22 A cm−2 K−2, which is very close to the theoretical value for n-type GaN/Pt contacts. As expected, the presence of defect states with different trap energy levels has a noticeable impact on the device electrical characteristics.

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PRESS RELEASE Technical and economic information selected by Knowmade

OPTOELECTRONICS

Veeco ships new-generation EPIK 868 MOCVD systems to China for high-volume LED production Source: Semiconductor Today

Epitaxial deposition and process equipment maker Veeco Instruments Inc of Plainview, NY, USA has shipped multiple TurboDisc EPIK 868 gallium nitride (GaN) metal-organic chemical vapor deposition (MOCVD) systems to several leading Chinese LED makers for the production of light emitting diodes for solid-state lighting applications. Compared with previous generations, the EPIK 868 MOCVD system enables cost per wafer savings of more than 20%, with a combined advantage of best operating uptime, low maintenance costs and what is claimed to be best-in-class wafer uniformity, as well as a compact architecture with the best footprint efficiency for high-volume LED production. “The introduction of the lower-cost and higher-productivity EPIK 868 to the China LED market clearly demonstrates Veeco’s long term commitment to this important region,” says president William J. Miller Ph.D. “With the EPIK 868, our Chinese customers can continue to take advantage of Veeco's leading edge technology development and world-class service offerings at a significantly lower cost of ownership,” he adds. Based on Veeco’s proven TurboDisc technology, the new EPIK 868 MOCVD system offers a four-reactor platform for the highest productivity and a 35% footprint reduction compared with the competition, it is claimed. Furthermore, the wafer carrier capacity can be increased for greater throughput per batch. “The EPIK 868 is built upon a production proven TurboDisc platform with over 1000 chambers installed worldwide, providing the highest operating stability and efficiency,” says Peo Hansson Ph.D., senior VP & general manager MOCVD Operations. “Not only will the new EPIK 868 system improve our customers’ productivity and cost of ownership, but it will also provide a highly reliable, leading-edge production tool,” he adds. The EPIK 868 features proprietary IsoFlange and TruHeat technologies, which provide homogeneous laminar flow and uniform temperature profile across the entire wafer carrier. These innovations produce wavelength uniformity to drive higher yields in a tighter bin. The EPIK 868 system offers a 2.3x throughput advantage over the existing EPIK 700 system due to its four-chamber configuration and the ability to increase wafer carrier capacity. Veeco says that customers can easily transfer processes from existing TurboDisc systems to the new EPIK 868 MOCVD platform for quick-start production of high-quality LEDs. Read more

glō orders Aixtron G5+ 8x150mm MOCVD system for micro-LED production Source: Semiconductor Today

Deposition equipment maker Aixtron SE of Herzogenrath, Germany has received an order for an AIX G5+ metal-organic chemical vapor deposition (MOCVD) platform from glō-USA Inc in Sunnyvale, CA, USA. Started at Lund University’s Nanometer Structure Consortium by professor Lars Samuelson, Sweden-based glō AB established an R&D and product development pilot line in Sunnyvale in 2010. The firm now focuses on

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commercializing micro-LED (mLED) products based on its proprietary defect-free gallium nitride (GaN) nanowire technology. Such 3D structures enable the growth of mLEDs while maintaining the reliability of an inorganic material system. Aixtron’s AIX G5+ Planetary Reactor system was selected in the scope of glō’s strategic expansion and will be delivered in an 8x150mm configuration during fourth-quarter 2017, as glō aims to deliver micro-LED products in 2018. According to glō, micro-LED technology is on the roadmap of all tier-one display makers as a challenger to the existing display technology for next-generation consumer products. Micro-LED displays consist of micron-sized LED arrays forming individual sub-pixel elements. Compared with existing LCD and OLED technologies, mLED displays offer low power consumption while exhibiting what is reckoned to be superior pixel density, contrast ratio and brightness, hence opening new horizons for consumer mobile products as well as premium TV displays. “Based on more than 10 years of experience and know-how in the area of nanotechnology, we have developed a game-changing three-color micro-LED display technology,” claims glō’s CEO Fariba Danesh. “Our three-color pixels are made solely with GaN semiconductor material. We are now focused on taking this exciting technology to a volume production stage. Beyond the epitaxial structure, the manufacturing of mLEDs require scalable processes, very tight uniformity and particle control of the epitaxial wafers to enable the highest yield and therewith cost-efficient transfer to our mLED partners. Aixtron’s AIX G5+ MOCVD system provides all these requirements while maintaining low fab economics due to a batch reactor configuration,” she adds. “Our AIX G5+ is being recognized as the tool of record for mLED-related applications as it is the sole technology on the market providing on-wafer uniformity control, low particle levels, and unique advanced features such as wafer-level temperature control with Auto-Feed Forward (AFF) and therefore supporting the demanding micro LED requirements,” claims Aixtron’s president Dr Bernd Schulte. Read more

Disruptive Substrate Technology for Direct Green and Red Micro LEDs Source: LED Inside

Figure 1. A full InGaN structure grown on InGaN-on-sapphire (InGaNOS) substrates can span the spectrum from blue to amber. (Source: Soitec)

The advantages presented by microLED displays include low power consumption, high resolution, quick response and high luminance. In addition, sensors can be embedded within these displays. But there are still numerous challenges ahead for microLED technology such as cost, supply chain, defect management, mass transferability and efficiency. In particular, the efficiency of green LEDs remains a challenge. In addition, microLED displays require the use of red, green and blue (RGB) LEDs, achieved by mixing nitride LEDs and phosphide LEDs. This mixing causes blue, green and red LEDs to behave differently in terms of temperature and aging, which impacts image color quality. Moreover, blue, green and red LEDs each require specific electronic drivers, making integration more complex. The ideal solution for microLED makers would be the availability of efficient nitride LEDs in both green and red. In this case, all RGB LEDs would be composed of the same material with the same behaviors and driving conditions. The challenge is to find one material capable of spanning the blue to red spectrum. Theoretically, the indium-gallium-nitride (InGaN) alloy can cover the entire visible range by adjusting the indium content to fine

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tune the peak emission wavelength. Unfortunately, high indium content in GaN-based LEDs results in poor quality because of lattice mismatches between the GaN buffer layers and the InGaN quantum wells. An innovative material solution To address these issues, Soitec has developed an innovative substrate called InGaNOX (InGaN-on-X) that overcomes lattice mismatch. The substrate has a top relaxed InGaN layer that can be used as a seed layer for full InGaN LED growth. The technology has been demonstrated in fabricating blue, green and red nitride emitting heterostructures on 100-mm wafers and is scalable up to 300-mm wafers. The starting material is an InGaN donor template typically formed by a 200-nm thick InxGa1-xN layer atop 3-µm thick GaN on sapphire, in which the indium content x varies from 1.5 percent up to 8 percent. The InGaN layer is strained because of the lattice mismatch between GaN on sapphire and the InxGa1-xN layer. The thin InGaN layer is then transferred using Soitec’s Smart Cut™ technology onto a compliant layer deposited on a substrate. Then the InGaN layer is patterned and all patterns are relaxed through a specific process developed by Soitec. To obtain final Ga-face polarity, a second transfer is performed onto the final handle wafer (figure 2).

Figure 2. (a) A 100-mm InGaNOS substrate is shown with an In0.08Ga0.92N layer and 300µm x 300 µm patterns at 3.205 angströms. The brown area is the patterned In0.08Ga0.92N layer. (b) This microscopic view shows a 300µm x 300 µm pattern with a top partially relaxed InxGa1-xN layer. (Source: Soitec)

Lattice parameters can be tuned from 3.190 angströms up to 3.205 angströms by the donor and relaxation process, enabling emissions from blue to red. Pattern size can be customized from square millimeters down to 5 µm x 5 µm. This methodology is compatible with sapphire, glass or silicon handle wafers with sizes up to 300 mm. Achieving green and red direct emission The benefits of relaxed InGaN substrates are demonstrated by the growth of full InGaN emitting heterostructures and their direct emission. These heterostructures have been grown and characterized by the electronics research institute CEA-Leti.

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Full InGaN LED heterostructures composed of a ~200-nm InGaN buffer layer followed by 5x InxGa1-xN/InyGa1-yN quantum wells are grown on InGaN-on-sapphire (InGaNOS) substrates with lattice parameters from 3.190 angströms up to 3.205 angströms. The expected well and barrier widths are 3 nm and 8 nm, respectively. According to the lattice parameters of the InGaNOS substrate, indium incorporation varies in the InxGa1-xN wells for the same growth conditions. Emission from the heterostructure can be tuned from green (537 nm) to red (617 nm) with FWMH of 46 nm and 75 nm, respectively.

Figure 3. Photoluminescence spectra at room temperature of full InGaN structures grown on InGaNOS 3.190 angströms (blue curve), InGaNOS 3.200 angströms (green curve), and InGaNOS 3.205 angströms (orange and red curves) are shown. (Source: Soitec)

An InGaNOS substrate enables full InGaN heterostructures with direct emission from blue to red (figures 1 and 3), whereas standard green LEDs are the product of blue LEDs and phosphor conversion and standard red LEDs are made from phosphide LEDs. The next step is the fabrication of optimized full InGaN LEDs with external quantum efficiency (EQE) measurement. A disruptive approach for microLED displays Soitec’s disruptive technology solution addresses the major challenges facing the microLED industry: - The substrates are suitable for producing high-efficiency green LEDs with direct emission, eliminating the need for phosphor converters. - Color quality consistency is enhanced with full InGaN blue, green and red LEDs that do not require nitride/phosphide LED mixing. In addition to producing high-efficiency and high-quality microLEDs, InGaNOX technology can be used to create substrates with mixed lattice parameters, enabling growth of different colored LEDs on the same substrate. This could drastically reduce the cost of microLED mass transfer for microdisplay fabrication. Read more

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LG Innotek exhibits UV LEDs at LED Japan Source: Semiconductor Today

At LED Japan 2017 in Makuhari Messe, Chiba, Japan (4-6 October), Seoul-based LG Innotek (a subsidiary of South Korean electronics company LG Group) is exhibiting about 30 types of UV LED packages (optimized on the basis of UV wavelength and optical power) as well as modules for sterilization (developed with the company's proprietary technologies) as it aims to make inroads into the Japanese market. In particular, the firm is introducing Japan’s first UV LED sterilizer for escalator handrails, emitting 275-278nm-wavelength light of to destroy germ DNA. The product can sterilize germs for the whole duration of escalator operation and is easy to install and manage, says the firm. Since the product was launched in Korea and China last July, it has been installed in about 30 locations, including shopping malls, hospitals and airports. LG Innotek is also showcasing UV-C LED modules for sterilization that can be installed in home appliances including water purifiers, air purifiers, etc. The firm will also show a cork sterilization module, installed in LG Electronics’ ‘PuriCare Slim Updown’ direct water purifier. Unlike mercury UV lamps, the module does not generate harmful heavy metals and, due to its durability, it does not easily break. In addition, LG Innotek is exhibiting 365, 385, 395, 405 and 415nm-wavelength UV-A LEDs that are used in curing equipment in manufacturing facilities. Curing hardens coating agents, adhesives etc or dries inks. The firm will show a 305nm UV-B LED, which is gaining attention for biotechnology and medical applications. Read more

Nitride Semiconductor files UV-LED patent infringement lawsuit in USA against Digi-Key Source: Semiconductor Today

Nitride Semiconductor Co Ltd of Tokushima, Japan has filed a patent infringement lawsuit with the US District Court for the District of Minnesota against Digi-Key Corp (trading as Digi-Key Electronics), which sells ultraviolet light-emitting diode (UV-LED) products on the Internet manufactured by Rayvio Corp of Haywood, CA, USA. Nitride is seeking injunction, damages and accounting, asserting that Digi-Key infringes its US patent 6,861,270 (‘Method for Manufacturing Gallium Nitride Compound Semiconductor and Light Emitting Element’) by selling UV-LED products manufactured by RayVio. The patented invention is said to contribute significantly to improving the light-emitting efficacy of LEDs. Previously, on 23 May, Nitride filed a lawsuit against RayVio in the US District Court, Northern District of California, alleging infringement of the same patent. Nitride says that, with professor Shiro Sakai at Tokushima University, in 2000 it succeeded in developing the first highly efficient UV-LED, and has since continued to manufacture and sell UV-LED, involving huge investment in R&D. The firm says that it will take resolute action against infringers in any country where appropriate and necessary to protect its patents and other intellectual property rights. Read more

Seoul Semiconductor sues Archipelago Lighting for infringement of 12 Acrich patents Source: Semiconductor Today

South Korean LED maker Seoul Semiconductor Co Ltd has filed a lawsuit, together with its affiliate Seoul Viosys Co Ltd, in the US District Court for the Central District of California asserting that Archipelago Lighting Inc is selling various LED bulb products (including filament LED bulbs) that infringe on 12 patents covering aspects of Seoul’s Acrich technology, including fundamental LED technologies such as LED driver technology for high-voltage operation, multi-junction technology (MJT), filament LED bulb structure, LED packaging, LED epitaxial growth, LED chip fabrication, etc.

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In conventional LED products, one LED unit usually operates at a low voltage (3V) and high current. To increase brightness, one must connect many LED units through wire-bonding, but this can lead to other issues such as an oversized, costly operating circuit, a substantial increase in manufacturing costs, and defects caused by multiple wire-bonding connections. Seoul’s Acrich technology resolves such problems by enabling the design of a high-voltage product with a high power output that relies on only a small number of LED units. It does so by utilizing its LED driver technology to enable high-voltage operation, as well as its unique MJT technology for mounting and integrating many LEDs within a small area. Acrich technology also enables LED products to operate using AC power without requiring conversion to DC, minimizing power dissipation and reducing overall component count. This maximises the available space in LED products, facilitating a simple circuit design and significantly reducing the size and cost of LED products, the firm says. Seoul began to develop Acrich technology in the mid-1990s and has continued to launch new Acrich products every year following mass production in 2005. Based on decades of investment in R&D, Seoul has established a large patent portfolio for Acrich technology, including rights to about 1000 patents. However, with the recent increase in demand for high-voltage LED products, several companies have begun to manufacture products that infringe on Acrich patents, says Seoul. To protect its investment against such infringement, Seoul says that it will actively enforce its patent rights against any infringers. “We have extensively investigated copycat products infringing on Acrich technology with various LED TVs, general lighting and automotive lighting products,” says Dr Ki-bum Nam, head of Seoul’s R&D Center & chief technology officer. “To protect Acrich technology, which has been developed with considerable resources over many decades, we will continuously take any and all legal action against infringers that disregard our valuable intellectual property,” he adds. “Creating a fair market that respects intellectual property is important for all innovative entrepreneurs and businesses.” Read more

HB-LED market growing at 10% CAGR to 2023 Source: Semiconductor Today

The high-brightness LED market will rise at a compound annual growth rate (CAGR) of 10% during 2016-2023, forecasts Occams Business Research and Consulting in its report ‘Global High Brightness LED Market Research Report Insights, Opportunity Analysis, Market Shares and Forecast, 2017 – 2023’. The key factors driving growth are increasing lighting applications, large-scale replacement of traditional luminaires, the decreasing cost of LED components, and the growing need for energy-efficient lighting products to save energy. Read more

HB-LED chip production to grow 2.8% to $13.179bn in 2017, then 2-5% annually during 2018-2022 Source: Semiconductor Today

Global production of high-brightness LED chips is expected to grow 2.8% year-on-year to US$13.179bn in 2017, then at 2-5% annually during 2018-2022, forecasts Digitimes Research. The production value for automotive and display applications will rise at a compound annual growth rate (CAGR) of 13-15% and 8-11%, respectively, in 2018-2022, while lighting will see a CAGR below 10% because LED lighting penetration will approach saturation, the firm adds. The production value for backlighting applications for TVs, notebooks, monitors and tablets will continue to decline slightly in 2018-2022, while backlighting applications for handsets will drop significantly due to the increasing adoption of AMOLED panels for smartphones. Read more

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ProPhotonix adds optical options to UV LED curing range, configurable to specific applications Source: Semiconductor Today

ProPhotonix Ltd of Salem, NH, USA, a designer and manufacturer LED illumination systems and laser diode modules for OEMs and medical equipment companies (as well as a distributor of laser diodes for Ushio, Osram, QSI, Panasonic and Sony) with operations in Ireland and the UK, has supplemented its range of COBRA Cure FX Series of UV LED curing systems with new optical options that provide higher intensity and dose, allowing end users to further optimize them to requirements of their specific application. Read more

Plessey’s LED fab scale-up could go abroad Source: Electronics Weekly

Plessey’s long-awaited LED manufacturing scale-up could be abroad rather than at the firm’s West Country fab, according to CEO and founder Michael LeGoff.

Plessey HQ Plymouth

At issue is a London-centric investment community, and a Government that ignores the UK semiconductor industry, according to LeGoff. Plymouth “The investment community doesn’t look at Plymouth, so we are looking to local government and the Government.” he said. “We are not saying give us £100m, we are saying support us in more tangible ways than just waving the flag.” He is thinking of something like last year’s Government decision to insist that “public sector steel contracts must specifically consider UK steel” – including in NHS and council projects. “The Government gets behind UK steel, automotive and nuclear power industries, but in electronics we are not supported,” said LeGoff. “It could easily say that if a company bids for a local government or government lighting contract, they get discount for UK-manufactured LED content.” “The US does it, so does Germany, France, Italy and China,” he added. “The thing is, the UK has to buy the LEDs, and if they don’t come from the UK, they will come from Taiwan.” LeGoff’s frustration is not just on behalf of Plessey. “We have got smart cars, smart cities and smart infrastructure coming – all needing sensors and CPUs,” said LeGoff. “All this needs to be manufactured here. Why shouldn’t that be here, and not china?

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Lobbying governments A similar call came from Europe earlier this year, when French semiconductor research lab Leti combined with the Fraunhofer organisation to lobby the French and German governments to assist in scaling European intellectual property to production in Europe rather than the Far East. “Otherwise,” said Fraunhofer microelectronics group chairman Hubert Lakner at the time, “Europe will become what it is geographically, an appendage of Asia.” Plessey added LED-making to silicon device production when it bought University of Cambridge GaN-on-silicon spin-out CamGaN in 2011/12. Using its chip-making expertise, the CamGaN intellectual property has been turned into a production process and Plessey LEDs can now match the performance of competitors, without the expense of working on sapphire or SiC substrates.

Plessey PLW7070GA

“Our 7070 [photo right] is coming out on par with Cree’s MK-R in efficacy,” Plessey operations director Mike Snaith told Electronics Weekly. Because the substrate is silicon, and Plessey has IC-grade lithography in-house, protection diodes and driver circuits can be integrated monolithically should the need arise, added Snaith. Scale-up is needed now because the firm has only two MOCVD reactors in which to grow the GaN layers necessary for LED production. Sub-scale “The product is profitable and selling into the US, Europe, China and Taiwan – and the Japanese are looking at our 3535,” said CEO LeGoff. “We have a £7m LED order book and we are gaining traction, but we are still sub-scale because we can’t generate enough sales to cover the cost of the factory with two reactors.” Space has been prepared in one of the firm’s clean rooms for two more reactors, and two reactors are reserved at the manufacturer. While UK investors are not interested in funding those reactors, international investors are, to boost their national productivity, said LeGoff. “I have tickets booked for meetings in the US, China and Taiwan. They want our LED scale-up,” he said, “and if I move production overseas, I then have to question if I maintain development in Plymouth.” “So why wouldn’t you want to scale production in Plymouth?” he added. Read more

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ELECTRONICS

Navitas’ co-founder delivering keynote on GaN power ICs at WiPDA 2017 Source: Semiconductor Today

Navitas Semiconductor Inc of El Segundo, CA, USA says that, at the 5th IEEE Workshop on Wide Bandgap Power Devices and Applications (WiPDA 2017) at the Hyatt Regency Tamaya Resort, Albuquerque, NM, USA, co-founder & VP of engineering Dr Nick Fichtenbaum will deliver a keynote address ‘GaN Power ICs: Device Integration Delivers Application Performance’ at 8:30am on 1 November. Fichtenbaum will also provide real-world insights in a panel discussion ‘Commercialization of GaN Devices in High-Frequency Power Electronic Applications’ at 10:30am on 31 October. “WiPDA is an influential forum as it brings together many of the best minds in power devices,” comments Fichtenbaum, who has been pioneering GaN materials and devices for nearly 15 years. “It is a great honor to present the latest in GaN technology including advances in the monolithic integration of analog, digital and power circuits all in GaN to solve fundamental challenges in high-speed, high density applications,” he adds. Founded in 2013, Navitas introduced what it claimed to be the first commercial GaN power ICs. The firm says that its proprietary 'AllGaN' 650V platform process design kit (PDK) monolithically integrates GaN power field-effect transistors (FETs) with logic and analog circuits, enabling smaller, higher-energy-efficiency and lower-cost power for mobile, consumer, enterprise and new energy markets. “Navitas has developed high-performance, easy-to-use GaN power ICs for next-generation applications in advanced mobile, industrial and consumer markets,” says VP of sales & marketing Stephen Oliver. “Fichtenbaum’s presentation highlights advanced research, practical development and real-world commercial implementation of this new GaN material,” he adds. “We look forward to discussing these GaN innovations as GaN adoption accelerates throughout the power industry.” In September, Navitas introduced what is claimed to be the smallest 65W USB-PD laptop adapter reference design in support of the dramatic size and weight reductions driven by market demand. The NVE028A uses Navitas high-frequency, high-efficiency AllGaN GaN Power ICs to deliver 65W in a package up to five times smaller and lighter than traditional silicon-based designs. Since introducing the AllGaN platform at APEC’16, Navitas has announced single and half-bridge GaN power ICs, plus the smallest 150W adapter. Read more

Navitas’ GaN power ICs enable smallest 65W USB-PD laptop adapter Source: Semiconductor Today

To keep pace with the dramatic size and weight reductions in laptop designs over the last 10 years, Navitas Semiconductor Inc of El Segundo, CA, USA has launched what it claims is the smallest 65W USB-PD (Type C) adapter reference design. Founded in 2013, Navitas introduced what it claimed to be the first commercial GaN power ICs. The firm says that its proprietary 'AllGaN' 650V platform process design kit monolithically integrates GaN power field-effect transistors (FETs) with logic and analog circuits, enabling smaller, higher-energy-efficiency and lower-cost power for mobile, consumer, enterprise and new energy markets.

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High-frequency, high-efficiency AllGaN Power ICs have been used to deliver 65W in only 45cc/2.7in3 and only 60g in weight by minimizing the size, weight and cost of transformers, filters and heat-sinks. By contrast, existing silicon-based designs can require 6-7in3 and weigh over 300g, says the firm. “Finally, a laptop adapter is thin and light – like the laptop it charges – and at a great price,” says VP of sales & marketing Stephen Oliver. “Power designers have been faced with several, conflicting industry challenges, from new USB Type C connectivity and USB PD (Power Delivery) output compliance to statutory energy-efficiency standards and the ever-present issue of cost,” he adds. “Navitas’ GaN power ICs deliver the simultaneous achievements of high-speed operation and high efficiency to enable a single system design that meets all of those challenges – at the same or lower cost than old, slow silicon designs”. The new NVE028A reference design uses GaN power ICs in an active clamp flyback (ACF) topology running 3-4x faster and with 40% lower loss than typical adapter designs, to deliver smaller size and reduced costs. The design is fully compliant with European CoC Tier 2 and US DoE Level VI efficiency standards, in addition to reaching peak efficiencies of over 94% at full load. “China power supply manufactures have been looking for wide-band-gap components like this, to further increase the power supply’s efficiency and power density to satisfy the requirement of customers,” comments Mark Dehong Xu, president of the China Power Supply Society (CPSS) and director of Zhejiang University’s Institute of Power Electronics. Unlike earlier attempts at high-density adapters, the NVE028A achieves small size (51mm x 43mm x 20.5mm cased) and what is claimed to be breakthrough power density (1.5W/cc, 24W/in3 cased) using simple, standard, low-cost manufacturing techniques. “Since we introduced the AllGaN platform at APEC’16, Navitas has announced single and half-bridge GaN power ICs, the world’s smallest 150W adapter, and now the world’s smallest, fully compliant 65W USB-PD design,” says Navitas’ CEO Gene Sheridan. “This is the flexible, high-performance, cost-effective platform that meets and exceeds the targets of the mobile and consumer charger markets”. Read more

Fujitsu Semiconductor and ON Semiconductor announce increased strategic partnership Source: ElectroIQ

Fujitsu Semiconductor Limited and ON Semiconductor (Nasdaq: ON) today announced an agreement that ON Semiconductor will purchase a 30 percent incremental share of Fujitsu’s 8-inch wafer fab in Aizu-Wakamatsu, resulting in 40 percent ownership when the purchase is completed. The purchase is scheduled to be completed on April 1, 2018, subject to certain regulatory approvals and other closing conditions. Read more

GaN power devices: Perfecting the vertical architecture Source: CompoundSemiconductor

By Yuhao Zhang, Min Sun and Tomás Palacios from Massachusetts Institute of Technology GaN is tipped to revolutionise the power electronics industry. It promises to trim the losses in power conversion circuits, and could drive a 10 percent reduction in global power consumption. What’s more, thanks to its capability to handle far higher power densities that today’s devices, it could trim the size, weight and cost of power systems. Initially, the development of GaN power devices focused on a lateral geometry. Recently, however, there has been a growing interest in vertical architectures. Merits of this geometry include: the capability of realising high

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breakdown voltage and current levels, without having to enlarge chip size; a superior reliability, resulting from the shift in the peak electric field from the surface to the bulk of the device; and a simplification of thermal management, compared with lateral devices. Thanks to these attributes, vertical GaN devices are the most likely contenders to combine currents in excess of 100 A with voltages of more than 600 V – the typical requirements for many medium and high power applications, such as electric vehicles and renewable energy processing. One of the challenges facing vertical GaN power devices – like their lateral cousins – is the realisation of normally-off operation. That’s not the only issue, however: many vertical devices require p-type GaN or epitaxial regrowth. That’s not easy, as compared to n-type GaN, the p-type variant has a low ratio for the acceptor activation and a far lower carrier mobility. And if epitaxial regrowth is needed, this greatly increases the complexity and cost of device fabrication. To overcome these difficulties, our team at the Massachusetts Institute of Technology has developed a novel GaN-based vertical power device that features trench and fin structures, and avoids the growth of p-type material. Enabling normally-off devices Trench structures are key building blocks in many modern GaN vertical devices. For example, they have been recently used in trench metal-insulator-semiconductor barrier Schottky rectifiers, where they shield the high electric field at the Schottky contact (see Figure 1 (a)). The addition of the trench greatly enhances the reverse blocking characteristics of the GaN Schottky rectifier by delivering a doubling of the breakdown voltage and a slashing of the leakage current at high reverse biases by a factor of 104.

Figure 1. Trench structures can feature in various vertical GaN power devices, including: (a) metal-insulator-semiconductor barrier Schottky rectifiers, (b) current aperture vertical electron transistors, and (c) MOSFETs.

Normally-off GaN transistors have also benefited from the addition of trenches. They include one of the most widely used vertical transistor architectures, the current-aperture vertical electron transistor. This normally-on device combines the high conductivity of a two-dimensional electron gas channel at the AlGaN/GaN heterojunction with the improved field distribution of a vertical structure. Normally-off operation is possible by switching to a trenched semi-polar gate (see Figure 1(b)). Another transistor architecture that benefits from the introduction of the trench is the vertical GaN MOSFET. This modification allows it to combine a normally-off operation with a low on-resistance (see Figure 1(c)). Read more

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Transphorm partner Yaskawa Electric’s new servo motor is first to use Gallium Nitride Source: I-micronews

Transphorm, the actor in the design and manufacturing of highest reliability (JEDEC and AEC-Q101 qualified) 650V gallium nitride (GaN) semiconductors, along with Yaskawa Electric announced that Yaskawa’s Σ-7 F is the first servo motor to use high-voltage (HV) GaN. Transphorm’s technology enables Yaskawa to deliver better performance in a smaller form factor versus what is possible with incumbent silicon semiconductors. The groundbreaking achievement of this co-developed device is that the Σ-7 F integrates the servo amplifier with the servo motor itself. Further, Yaskawa’s use of Transphorm’s GaN FETs produces an integrated servo motor half the size of a similar design using Silicon (Si) technology.

TheΣ-7 F: Revolutionized by GaN

The Σ-7 F series—AC servo motors in a three-phase bridge configuration—uses Transphorm’s HV GaN FETs in a standard three lead TO-220 package. The topology will be deployed across Yaskawa’s full Σ-7 F product line, which currently includes three servo motors ranging from 100W to 400W. The integrated motor allows the industrial manufacturing system to simplify cabling in a daisy chain configuration. Further, it reduces the system’s control panel cabinet size by as much as 30 percent, given:

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· Reduction in size of the servo motor itself · Elimination of the power supply cable’s terminal block due to a reduction in cabling required · Smaller heat sink due to lower losses using Transphorm GaN Transphorm’s HV GaN technology inherently delivers better efficiency via lower gate charge, faster switching speeds and smaller reverse recovery charge when compared to incumbent technologies, while offering high reliability. Additionally, applications designed on Transphorm GaN achieve smaller device size, higher power density and lower overall system costs. Yaskawa’s Σ-7 F motor demonstrates these benefits as well as:

The Σ-7 F targets industrial multi-axis automation systems commonly used in conveyance equipment as well as food product and packaging manufacturing. Such automation systems must provide high precision, high throughput, repeatability and design flexibility. Read more

RF GaN market growing at CAAGR of 14.1% to $733m in 2021, maintained by defense applications Source: Semiconductor Today

RF gallium nitride (GaN) device revenue rose by slightly more than 23% in 2016, and will increase at a compound annual average growth rate (CAAGR) of 14.1% to $733m in 2021, forecasts the Strategy Analytics Strategic Component Applications (SCA) group report ‘RF GaN Market Update: 2016-2021’, as fast growth in defense applications - particularly radar, communications and electronic warfare (EW) - will offset an expected flattening of the wireless infrastructure segment to keep the overall market growth for GaN on an upwards trajectory. “LTE base-station deployments in China have been the obvious growth driver for RF GaN revenue these past three years,” comments Eric Higham, service director, Advanced Semiconductor Applications (ASA) service. “As this activity winds down, infrastructure will remain a large and important segment, but the industry will need to position to take advantage of other applications and emerging 5G opportunities for growth,” he adds. Key questions that the RF GaN device supply base needs to understand are listed as:

• How will the GaN equipment/supplier landscape change over time?

• What product platforms will be important?

• What are the technology/product differentiators?

• Where is the next big commercial application for RF GaN? “While the GaN supply chain looks for guidance on these future commercial opportunities, fast growth in defense applications will keep the overall market growth for GaN on an upwards trajectory,” notes Asif Anwar,

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director of the Advanced Defense Systems service. “The question is, can companies focused exclusively on domestic defense sectors take advantage of this growing global demand? These companies will need to understand how to better compete against commercial manufacturers as well explore strategic options including partnerships or secondary manufacturing options.” Read more

EPC2045 100V GaN-on-Silicon Transistor Source: I-micronews

Take a look at the fifth generation of EPC’s low voltage transistor The low voltage GaN device market is increasingly important, and Efficient Power Conversion Corporation (EPC) is a major player in low voltage GaN-on-silicon high-electron-mobility transistor (HEMT) devices. 100V GaN HEMTs are a very new technology but they already compete with silicon transistors, especially in the field of megahertz high frequency applications. System Plus Consulting has investigated the company’s EPC2045 device, its latest driving 100V for applications such as single-stage 48V converters, USB-C data and power connectors, LiDAR sensors, point-of-load converters and loads in open rack server architectures.

EPC2045 GaN on Silicon Transistor 100V (System Plus Consulting)

With its new transistor and GaN epitaxy design, the EPC2045 achieves a breakdown voltage of 100V for a current of 16A at 25°C, and a very low RdsOn on-resistance of 7mΩ compared to the previous generation. The chip-scale packaging of EPC products reduces the final device cost and decreases its inductance, bringing advantages not only with respect to competitors in GaN, but also silicon. Compared to silicon transistors, GaN process developments have significantly lowered capacitance. This translates into lower gate drive losses and lower device switching losses at higher frequencies for the same on-resistance and voltage rating.

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EPC2045 GaN on Silicon Transistor 100V (System Plus Consulting)

Based on a complete teardown analysis, the report also provides an estimation of the production cost of the epitaxy and the package. The report also compares the new product with previous EPC devices and epitaxy and GaN Systems, Transphorm, Panasonic and Texas Instruments packaging. This comparison highlights the differences in design and manufacturing processes and their impact on device size and production cost. Finally, the report shows a comparison between the standard 100V silicon MOSFETs and the EPC GaN-on-silicon HEMT. Read more

EPC launches wireless power demonstration kits Source: Semiconductor Today

Efficient Power Conversion Corp (EPC) of El Segundo, CA, USA - which makes enhancement-mode gallium nitride on silicon (eGaN) power field-effect transistors (FETs) for power management applications - has announced the availability of two new demonstration kits: the EPC9127 (a complete wireless power kit including a 10W, class 2 amplifier, category 3 receiver device) and the EPC9128 (consisting of a 16W, class 3 amplifier and two receiver devices - categories 3 and 4). Coupled with the existing EPC9120 (33W class 4) and the EPC9121 multi-mode kit (capable of operating to either an AirFuel Class 2 standard with a category 3 device or a Qi (A6)/PMA standard with a compatible receiving device), these systems provide a full range of wireless power demonstration kits to allow for complete, wide-spread implementation. EPC hence now covers a wide range of the AirFuel resonant technology standard. The popularity of resonant wireless power transfer is increasing rapidly, with end applications evolving quickly from mere cell-phone battery charging to the powering of large surface areas where handheld tablets, laptops and computers – and, soon TV sets, lamps and other electrically powered appliances – can simultaneously charge anywhere on the surface. The purpose of the demonstration kits is to simplify the evaluation process of using eGaN FETs and ICs for highly efficient wireless power transfer. Operating at 6.78MHz (the lowest ISM band), the kits utilize the high-frequency switching capability of EPC’s GaN transistors to facilitate wireless power systems. The efficiency of the systems is about 87% from input to the amplifier to the output of the receiver (end-to-end). With future improvements in architecture and GaN IC technology, this can reach the 95% range, reckons EPC. Read more

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EPC appoints MIGVAN as sales, marketing and technical support partner for Israel Source: Semiconductor Today

To support its accelerating growth throughout Israel, Efficient Power Conversion Corp (EPC) of El Segundo, CA, USA – which makes enhancement-mode gallium nitride on silicon (eGaN) power field-effect transistors (FETs) for power management applications – has appointed MIGVAN Technologies & Engineering Ltd as its sales, marketing and technical support representative. Read more

EPC presenting GaN-based large-surface-area wireless power solution at Wireless Power Summit Source: Semiconductor Today

At the Wireless Power Summit 2017 in the Embassy Suites Hotel Downtown, Denver, CO (5-6 October) , Efficient Power Conversion Corp (EPC) of El Segundo, CA, USA - which makes enhancement-mode gallium nitride on silicon (eGaN) power field-effect transistors (FETs) for power management applications - is exhibiting a wireless power tabletop highlighting the capability of GaN-based magnetic resonance technology to provide wireless power over a large surface area to many receiving devices (such as cell phones, laptop computers, and table lamps) simultaneously. The future of wireless power and its eventual ubiquitous adoption is dependent on the ability of end users to place any electrical item on a surface and have it powered without having to ‘plug in’, says EPC. The fundamental technology to achieve this ‘drop-and-go’ power is defined by the AirFuel Alliance standard. eGaN FETs and ICs, operating at 6.78MHz, are featured in the amplifiers that power the transmit coils of the wireless power surface and in the receive circuits used in the devices placed on the surface. eGaN technology is suitable for wireless power applications due to its ability to operate at high frequency, high voltage, and high power, says EPC. The wireless power table being demonstrated at the Summit is capable of delivering a total of 165W of power, enabling simultaneous powering of multiple devices. Several eGaN products are critical to the wireless power table design. Specifically, the amplifier on the transmit side of the table uses the EPC9512 power amplifier. The amplifier takes advantage of the performance of the EPC8010 as the main power stage FET, the EPC2038 as the synchronous bootstrap FET and the EPC2019 is critical in the SEPIC pre-regulator. On the receive side, the EPC2019 is also used as a boost FET to accommodate the multiple power levels of the receive devices to be placed on the tabletop, which range from 5W for cell-phone charging to 25W to power the laptop. The Wireless Power Summit will also provide wireless power industry forecasts, showcase the latest technologies, and give current insights into the wireless power market. Read more

EpiGaN to supply OMMIC with GaN/Si material for new 150mm RF power product line Source: Semiconductor Today

EpiGaN nv of Hasselt, near Antwerp, Belgium - which supplies gallium nitride on silicon (GaN-on-Si) and gallium nitride on silicon carbide (GaN-on-SiC) epitaxial wafers for power switching and RF power devices as well as sensors - and OMMIC of Limeil-Brévannes, France, which provides compound semiconductor monolithic microwave integrated circuits (MMICs) and foundry services, are collaborating to develop RF GaN/Si technology on 150mm-diameter wafers. OMMIC recently inaugurated what is reckoned to be Europe’s first 150mm GaN production line. The firms have jointly collaborated on establishing a production process based on EpiGaN’s GaN/Si material technology with in-situ grown silicon nitride (SiN) passivation. They will also cooperate directly to move this

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technology to 150mm-diameter wafers, targeting future 5G wireless communication standards, for which OMMIC last week announced a large project with a 5G equipment supplier. The advent of the 5G era about to revolutionize long-distance communications, says EpiGaN. In order to provide users with exceptionally high-speed wireless connections, ultra-low latency and enhanced mobile broadband, gallium nitride is required - in applications such as multimedia streaming, autonomous driving, machine-to-machine communication with billions of interconnected sensors or Internet-of-Things (IoT) - to transmit and receive RF signals in the utmost efficient way, add the firm. “We offer many attractive USPs for RF power, which add value to device designers, such as in-situ SiN passivation for enhanced device robustness, or very low RF losses up to 100GHz,” says EpiGaN’s CEO Dr Marianne Germain. The high-frequency capability of the firm’s material “enables a very cost-efficient and energy-efficient GaN technology for the higher frequency bands targeted by 5G,” she adds. “The next-generation 5G standard will require GaN as an enabling semiconductor technology to provide a step-up in performance,” states OMMIC’s CEO Dr Marc Rocchi. “Only then will the experience for the end user be superb. Teaming up with EpiGaN is an essential element of our growth strategy and it enables us to meet the required volume and quality levels for our 5G GaN MMICs,” he adds. Read more

eLASER orders further Aixtron AIX G5+C MOCVD system to scale up GaN epi and device capacity for power electronics Source: Semiconductor Today

Deposition equipment maker Aixtron SE of Herzogenrath, near Aachen, Germany says that Elite Advanced Laser Corporation (eLASER) of Chung Ho Dist, New Taipei City, Taiwan, which provides electronics manufacturing services (EMS) for optoelectronic and radio frequency (RF) components, has placed a repeat order for an AIX G5+C metal-organic chemical vapor deposition (MOCVD) system to produce gallium nitride (GaN) epitaxial wafers and devices for power electronics applications. The production tool will be installed during second-half 2017, complemening existing capacity. It integrates Penta-Injector technology (for best material uniformities across the entire wafer diameter) and is equipped with a cassette-to-cassette (C2C) wafer transfer module for full automation of GaN processes. “We have been impressed by the speed at which eLASER has transferred their device manufacturing processes on our system technology. Therefore, we are convinced that the recent addition of our AIX G5+C platform - which has become the tool of record at leading GaN power electronics manufacturers - will support the company’s goal to gain further market share in the GaN power electronics ecosystem,” comments Aixtron’s president Dr Bernd Schulte. “While offering configurations of 8x150mm and 5x200mm, the tool meets the toughest requirements from the silicon industry in terms of uniformity and particles. Thereby, Aixtron’s G5+C system technology is breaking down the barriers to bring GaN into silicon production lines.” Read more

Wolfspeed highlighting GaN RF technology and GaN-on-SiC foundry services at CSICS Source: Semiconductor Today

In booth #200 at the 2017 IEEE Compound Semiconductor Integrated Circuit Symposium (CSICS) in Miami, FL (22–25 October), Wolfspeed of Raleigh, NC, USA — a Cree Company that makes silicon carbide (SiC) power products and GaN-on-SiC high-electron-mobility transistors (HEMTs) and monolithic microwave integrated circuits (MMICs) — is exhibiting its GaN RF amplifier technology and showcasing its GaN-on-SiC commercial

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foundry services, enabling RF design engineers to build more efficient broadband power amplifiers for commercial and military wireless communications and radar applications. Wolfspeed engineers will be showcasing the firm’s commercial open GaN-on-SiC foundry services, as well as demonstrating their latest GaN-on-SiC power devices for an extensive range of RF power amplifier applications for military communications systems, radar equipment, electronic warfare (EW) and electronic counter-measure (ECM) systems, as well as commercial RF applications in the industrial, medical & scientific (ISM) band. Wolfspeed claims that its GaN RF technology leads the industry in reliability with a failure-in-time (FIT) rate of <10 after billions of device hours of field operation. “As GaN-on-SiC RF technology has entered the mainstream in commercial wireless infrastructure, our industry-leading open RF foundry and components business continues to innovate to meet the changing cost, efficiency and performance demands needed for upcoming 5G systems,” says Jim Milligan, vice president, RF and Microwave Products. Wolfspeed’s RF business development manager Simon Wood serves as the exhibition chair of the CSICS conference, and Wolfspeed personnel are presenting one of the CSICS 2017 conference technical sessions. On 25 October at 1:30pm, RF applications engineer Kasyap Patel will deliver a presentation ‘Current Contours-Based Input Matching Network (IMN) Design Methodology for Broadband GaN Doherty Power Amplifiers’. Co-presenters for this session are H. Golestaneh (RF/mmWave design engineer at Peraso Technologies) and S. Boumaiza (professor, ECE at University of Waterloo, Canada). Read more

Mitsubishi Electric launching Ka-band GaN-HEMT MMIC to downsize satellite earth-station power transmitters Source: Semiconductor Today

Following development that was partially supported by Japan’s New Energy and Industrial Technology Development Organization (NEDO), Tokyo-based Mitsubishi Electric Corp is to launch the MGFG5H3001, a Ka-band (26–40GHz) 8W gallium nitride (GaN) high-electron-mobility transistor (HEMT) monolithic microwave integrated circuit (MMIC) amplifier for satellite earth stations. Satellite networks (used for high-speed communication during natural disasters and in areas where ground networks are difficult to construct) are currently implemented mainly in the C-band (4–8GHz) and Ku-band (12–18GHz), but higher frequencies are increasingly being used. Also, market demand for deployments in the higher-frequency Ka-band are increasing.

Picture: The new MGFG5H3001 Ka-band GaN-HEMT MMIC.

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The new Ka-band GaN-HEMT MMIC is targeted at helping to meet the growing demand for higher-frequency deployments, as well as facilitating the development of satellite communications equipment capable of extra-high output power and efficiency. With an optimized transistor configuration on one chip that integrates amplifier transistors circuits, matching circuits and distortion-reducing linearizer, the MGFG5H3001 offers what are claimed to be industry-best low distortion and saturated output power rating (Pout typical) of 39.0dBm (8W). The reduced number of parts yields a small footprint that can help to downsize satellite earth-station power transmitters. Samples of the MGFG5H3001 are shipping from 1 November. Read more

GaN Systems and Taiwan’s Ministry of Economic Affairs collaborate on GaN technology to meet global power challenges Source: Semiconductor Today

GaN Systems Inc of Ottawa, Ontario, Canada – a fabless developer of gallium nitride (GaN)-based power switching semiconductors for power conversion and control – and Taiwan’s Ministry of Economic Affairs (MOEA) have entered into a Letter of Intent to collaborate on expanding the economic and technical benefits of GaN technology to Taiwan’s electronics manufacturers. The aim is to meet the global challenges of unsustainable increases in power consumption, combating climate change, implementing cleantech technologies, and meeting green CO2-reduction initiatives. To further advance Taiwan’s role in the electronics industry, recognizing the importance and benefits of GaN, the MOEA will provide assistance to GaN Systems to extend its in-country business and representation. This agreement brings together the GaN transistor manufacturer with the government body that oversees Taiwan’s electronics industry. Working together, the alliance will collaborate to help solve global power challenges.

Picture: GaN Systems and Taiwan’s Ministry of Economic Affairs sign Letter of Intent.

“As Taiwan plays a preeminent role in the Asian electronics industry, we are pleased to provide GaN Systems with the resources to continue their success with our leading manufacturers,” says Mei-Hua Wang, Vice Minister of Taiwan’s Ministry of Economic Affairs (MOEA). “This Letter of Intent strengthens the bonds between GaN Systems and Taiwan’s electronics industry,” she adds.

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“We see this as an important demonstration of how companies and government work together to reinforce partnerships amongst industry leaders and across industry segments,” comments GaN Systems’ CEO Jim Witham. Read more

MACOM showcasing GaN-on-Si portfolio and high-performance MMICs and diodes at EuMW Source: Semiconductor Today

In booth #200 at European Microwave Week (EuMW 2017) in Nürnberg Convention Center, Germany (10–12 October), M/A-COM Technology Solutions Inc of Lowell, MA, USA (which makes semiconductors, components and subassemblies for analog RF, microwave, millimeter-wave and photonic applications) is showcasing its gallium nitride-on-silicon (GaN-on-Si) portfolio and other high-performance monolithic microwave integrated circuits (MMICs) and diode products. The booth features new products optimized for base-station, aerospace and defense, RF energy, commercial, and industrial, scientific & medical RF applications, namely:

• high-power GaN-on-Si (RF Energy Toolkit enabling faster and easier solid-state RF system development, and a 500W GaN-on-Si device with high efficiency and power at elevated temperature, suitable for rugged aerospace & defense applications);

• RF small-signal portfolio (featuring high-performance MMICs and base-station and mobile backhaul devices);

• high-performance diodes (diode design and application-specific solutions); and

• high-reliabiity (hi-rel) and component devices (the latest screened products for mission-critical aerospace applications).

• Members of MACOM’s product management, engineering and applications teams will be available in the booth.

Read more

MACOM launches 500W GaN-on-Si power transistor for L-band airport surveillance radar Source: Semiconductor Today

M/A-COM Technology Solutions Inc of Lowell, MA, USA (which makes semiconductors, components and subassemblies for analog RF, microwave, millimeter-wave and photonic applications) has launched the newest entry in its gallium nitride on silicon (GaN-on-Si) power transistor portfolio for pulsed L-band radar systems targeted for airport surveillance radar (ASR) applications at 1.2-1.4GHz. Delivering high efficiency at peak pulse power levels up to 500W, the MAGX-101214-500 is expected to outperform premium-priced GaN-on-SiC-based transistors, and far exceed the performance, efficiency and power density of legacy silicon LDMOS-based devices. The new MAGX-101214-500 enables customers to scale to higher power levels across a host of ASR applications, delivering 500W output power and greater than 70% power efficiency under pulsed conditions at 50V operation. Supplied in a small-footprint ceramic flanged package and supporting matching structures that minimize circuit size, the transistors help to enable rugged, compact radar systems underpinned with efficient, simplified cooling and power supply architectures, says MACOM. The MAGX-101214-500 builds on MACOM’s portfolio of GaN-on-Si power transistors, which have demonstrated field-proven reliability in harsh environmental conditions. To date, over 1 million MACOM GaN-on-Si devices have been shipped to customers around the world.

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“The continued expansion of MACOM’s GaN-on-Si product portfolio enables customers to address an ever-widening range of RF power requirements while achieving performance profiles that meet and exceed GaN-on-SiC, at significantly less cost at scaled volume production levels,” claims Greg French, senior product manager, RF Power. “Our proven technology leadership in GaN-on-Si combined with our decades-long heritage in civil and defense radar are among the many factors fueling our innovation in these important markets.” MACOM is showcasing the MAGX-101214-500 in booth #200 at European Microwave Week (EuMW 2017) in Nuremberg, Germany (10-12 October). Products are sampling to customers now, with production release targeted for first-half 2018. Read more

MACOM’s RF Energy Toolkit now available for commercial OEMs designing GaN-on-Si-based RF systems Source: Semiconductor Today

M/A-COM Technology Solutions Inc of Lowell, MA, USA (which makes semiconductors, components and subassemblies for analog RF, microwave, millimeter-wave and photonic applications) says that its RF Energy Toolkits are now available for order, meeting surging demand for a flexible and cost-effective development platform that helps to accelerate time to market with high-performance, power-efficient solid-state RF systems. Targeted for use in commercial markets ranging from cooking, lighting and industrial heating/drying to medical/pharmaceutical, automotive ignition systems and beyond, the RF Energy Toolkits enable engineers to quickly and easily take advantage of GaN-on-Si as a high-precision, high-efficiency energy source, says MACOM. The firm says that the all-in-one versatility and ease-of-use of its RF Energy Toolkit streamlines development cycles and costs for GaN-on-Si-based RF systems, equipping engineers to overcome the limitations of legacy magnetron power sources while achieving significantly higher efficiency than silicon LDMOS-based systems, at comparable cost structures. Designers can fine-tune RF energy output for any application requirements, with push-button ease and an intuitive display interface. OEMs designing for more complex RF energy applications can tap MACOM and its partner network for custom applicator and algorithm development, plus expert engineering support. The RF Energy Toolkits can scale power output up to 300W leveraging the onboard MACOM GaN-on-Si power transistor, and can be paralleled for higher-power applications. The Toolkits support pulsed and continuous-wave operation at the 2.45GHz frequency band. Future Toolkits will support the 915MHz frequency band. “Commercial OEMs have awakened to the massive market opportunity for GaN-on-Si-based solid-state RF systems which essentially remove most of the limitations of magnetron-based systems, but they are new to this technology, and design and development challenges have slowed their time to market – until now,” says Mark Murphy, senior director, RF Power. “The RF Energy Toolkit affords them an all-in-one, adaptable ‘Swiss army knife’ solution that removes the engineering barriers that have impeded OEMs’ adoption of RF energy, liberating them to take giant strides forward on the path to mainstream commercialization,” he adds. MACOM is showcasing its RF Energy Toolkit in booth #200 at European Microwave Week (EuMW 2017) in Nuremberg, Germany (10-12 October). RF Energy Toolkits are available for order now. Read more

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Custom MMIC discussing latest in RF MMICs at EuMW Source: Semiconductor Today

On stand 113 at European Microwave Week (EuMW 2017) in Nuremberg, Germany (8-13 October), monolithic microwave integrated circuit developer Custom MMIC of Westford, MA, USA is discussing its latest developments in RF and microwave gallium arsenide (GaAs) and gallium nitride (GaN) MMICs, including ultra-wideband amplifiers, linear mixers, low-noise amplifiers (LNAs), low-phase-noise amplifiers (LPNAs), and switches. On 11 October at 2:10pm in the Kiew room - as part of the 47th European Microwave Conference’s EuMC28 sessions on amplifiers and receivers - lead engineer Nicholas Novaris is presenting a paper ‘Understanding the Phenomenon of High Power Pulse Recovery in GaN LNAs’, which explores and details the high-power pulse recovery behavior of commercially available and overdriven GaN LNAs. This topic has become pertinent as GaN LNAs, with comparable noise figures to commonly installed GaAs LNAs, are capable of withstanding much higher input power levels than GaAs, and have the added benfit of not requiring additional and performance-degrading limiter circuitry, says Custom MMIC. Read more

StratEdge’s molded ceramic packages meet GaN Mil-Std packaging requirements up to 18 GHz Source: Semiconductor Today

StratEdge of San Diego, CA, USA (which designs and produces packages for microwave, millimeter-wave, and high-speed digital devices) says that its off-the-shelf line of molded ceramic packages can be configured to meet the requirements for chips with frequencies up to 18GHz, including gallium nitride (GaN) devices. The firm’s molded ceramic packages come in over 200 standard outlines, dramatically increasing the packaging options for GaN devices. StratEdge also offers complete automated assembly & test services for these packages, including gold-tin solder die attach.

Picture: StratEdge’s MCB GaN package.

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GaN devices are traditionally packaged in StratEdge’s LL family of high-power laminate copper-moly-copper (CMC) base packages with a ratio of 1:3:1 CMC, accommodating frequencies up to 63GHz. In the molded ceramic package, the standard Kovar base can be replaced with CMC. For frequencies of 18GHz or less, using a molded ceramic package provides the advantages of hermeticity, a broad array of outline packages and lower cost, while the CMC provides the heat dissipation needed for GaN devices to meet requirements for aerospace applications. For surface-mount (SMT) applications, the packages can be manufactured with gull-wing formed leads, offering flexibility since it is inexpensive to change the lead design to match an existing footprint. “StratEdge has hundreds of molded ceramic MC Series packages in standard, open-tooled configurations, which are all Mil-Std hermetic,” says president Tim Going. “By swapping out their bases with CMC, you get a low-cost, high-power, fully hermetic packaging solution.” StratEdge is exhibiting at the 2017 IEEE Compound Semiconductor Integrated Circuit Symposium (CSICS) in Miami, FL, USA (22-25 October). Read more

Nitride epiwafer firm SweGaN raises $750,000 in new share issue Source: Semiconductor Today

In a new share issue, custom III-nitride epiwafer maker SweGaN of Linköping, Sweden has raised SEK6m ($750,000) from existing investors US-based Mount Wilson Ventures, Almi Invest and Linköping University’s LiU Invest together with several private angel investors. Founded in 2014, SweGaN has developed patented nitride-based epitaxial structures aimed at meeting the challenges of high-performance and high-frequency gallium nitride (GaN) devices, targeting a wide range of applications including telecoms for 5G networks, satellite communications, and defense or civilian sensors. “The investment is further supplemented by a loan that gives us a great opportunity to grow rapidly,” says CEO Olof Kordina. “The funds raised will be used to increase production and accelerate the development of our new materials,” he adds. The strategy is to increase and improve production to meet the growing demand for high-quality epitaxial wafers. Production capacity is to be increased by a factor of five, and by the beginning of 2018 the firm will start producing on 6-inch substrates instead of the existing 4-inch substrates. By the end of 2017 SweGaN expects to see revenue growth of 300%, the employment of three new staff, and the launch of a new product range. Read more

WIN enhances 0.25µm GaN power process Source: Semiconductor Today

WIN Semiconductors Corp of Taoyuan City, Taiwan – the largest pure-play compound semiconductor wafer foundry – has released an optimized version of its 0.25µm gallium nitride (GaN) technology, NP25, that provides what is claimed to be superior DC and RF transistor performance. In production since 2014, NP25 is a 0.25µm-gate gallium nitride on silicon carbide (GaN-on-SiC) process, and offers the flexibility to produce both fully integrated amplifier products as well as custom discrete transistors. The optimized 0.25µm process offers enhanced RF performance with fast switching time, higher gain and increased power-added efficiency (PAE) for demanding power applications through Ku-band. Optimized NP25 transistors exhibit better DC and RF current-voltage (IV) characteristics and provide 2dB higher maximum stable gain. Increased gain leads directly to higher power density and PAE under a range of tuning and

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bias conditions. This performance-optimized process is fully qualified and supported with a comprehensive design kit and transistor models. WIN’s NP25 technology is fabricated on 4-inch silicon carbide substrates and operates at a drain bias of 28V. At 10GHz, NP25 provides saturated output power of 5W/mm with 19dB linear gain and over 65% power-added efficiency. These performance metrics make the NP25 process suitable for a variety of high-power, broad-bandwidth and linear transmit functions in the radar, satellite communications, and wireless infrastructure markets. NP25 sample kits are available and can be obtained by contacting WIN’s regional sales managers. WIN is showcasing its compound semiconductor RF and mm-Wave solutions in stand 111B at European Microwave Week (EuMW 2017) in Nurnberg, Germany (8-13 October). Read more

Saab using GaN-based AESA in new Arexis electronic warfare jammer pod for Gripen fighter aircraft Source: Semiconductor Today

Sweden-based defence and security company Saab AB is in the final stages of development of a new family of electronic warfare (EW) self-protection systems called Arexis. One version of Arexis is the on-board EW suite in the new version of the Gripen fighter, Gripen E/F. At the Defence and Security Equipment International (DSEI 2017) exhibition in London, UK (10-13 September), Saab expanded the Arexis product family by presenting the Arexis advanced electronic attack jammer pod. This has the capability to screen and hence protect the approach and departure of entire strike formations against low-frequency radars by the smart utilization of DRFM-based jamming techniques such as smart noise, coherent false targets, and various saturation techniques. The core technologies in Arexis are ultra-wideband digital receivers and DRFM (digital radio frequency memory) devices, gallium nitride (GaN)-based solid-state active electronically scanned array (AESA) jammer transmitters, and interferometric direction finding systems. For the advanced electronic attack application, these technologies are adapted to the lower-frequency ranges that are required to jam modern anti-stealth air defence systems, the output power is increased, and everything is repacked in a pod to make it a role-specific solution. Saab EW systems are in use by customers worldwide. The firm can provide everything from electronic support measures, radar warner receivers and jammers to self-protection systems with missile approach warners and countermeasure dispenser systems. Read more

Energous launches GaN-based wireless solution for charging electronic devices with up to 10W Source: Semiconductor Today

Energous Corp of San Jose, CA, USA (a developer of WattUp wire-free RF charging technology that provides over-the-air power-at-a-distance) has launched a high-power Near Field WattUp charging solution for electronic devices such as smartphones, tablets, smart speakers, game controllers, drones etc. The new high-power Near Field WattUp charging solution includes: a GaN-based 5-10W RF receiver IC; a GaN-based 10-15W RF power amplifier (PA); allowance for full 2D/planar movement; support for 90˚ charging angles (sideways charging); a smaller receiver (RX) size, superior accomodation of metal and other foreign objects; and PA integration into the overall system, leading to a lowered bill-of-materials (BOM) cost.

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The new transmitter reference design can charge devices with up to 10W of energy, significantly increasing the amount of power delivered to receiving devices and eliminating connectors and charging contacts for a much wider variety of devices. “We continue to grow our WattUp wire-free charging ecosystem with reference design solutions that will support the technology adoption in an even broader range of customer products,” says president & CEO Stephen Rizzone. “Extending the high-power capabilities of Near Field WattUp charging enables many different types of devices to be charged from multiple transmitter options. By continuing to expand the portfolio of reference designs available to customers, we are able to support increasing requests from our various partners for additional options and power levels,” he adds. “With a catalog of reference designs ranging from high-power, quick-charging, low-power, small-form-factor, Mid Field and Far Field power-at-a-distance, customers now have the ability to meet virtually all of their wireless charging requirements from a single source,” comments Mark Tyndall, senior VP of corporate development & strategy at Dialog. “These first GaN-based solutions for our WattUp wire-free charging technology support higher power and improved charging flexibility,” says founder & chief technology officer Michael Leabman. “Our ability to develop multiple components within the WattUp ecosystem allows us to innovate based on our customer needs,” he adds. Read more

Eltek’s Flatpack2 SHE power conversion module uses Infineon’s CoolGaN tech Source: Power Electronics News

In close co-operation with Infineon Technologies, Eltek engineers have reduced losses by as much as 50% while further improving reliability and total cost of ownership in their Flatpack2 SHE, a new Super High Efficient power conversion module in the Flatpack2 family. Eltek leveraged HE technology with CoolGaN from Infineon to reach up to 98% efficiency in the devices. Examples of the energy savings are illustrated by these examples where early versions of the 92%-efficient Flatpack 2 were replaced with Flatpack 2 SHE: -Single mobile base station in Italy, 6 kW load – annual saving: € 576.00 -Central office site in UK, 250 kW load – annual saving: £ 18,350.00

“We always seek to stay ahead of the game on technology, and the ability to take on game changing technology like the CoolGaN from Infineon is key to achieve this goal. Besides the efficiency improvement, this technology brings improved reliability as well as manufactureability and other advantages that will enable us to continue to spearhead this industry,” said Erik Myhre, Senior R&D Manager at Eltek.

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For more information visit www.infineon.com/GaN Read more

OMMIC Develops First European 6-inch GaN Wafer Production Fab Source: Everything RF

France based MMIC manufacturer, OMMIC has announced the inauguration of its new 6-inch GaN production line. The new facility will multiply OMMIC’s manufacturing strength exponentially, making it one of Europe’s leading III-V compound semiconductor suppliers and the only European company able to produce GaN and GaAs on 6-inch wafers.

Based out of the city of Limeil-Brévannes, France, OMMIC, with a turnover of €14.5 million in 2016 and a backlog of more than €20 million this year, was the 5th largest company manufacturing MMICs. The company is now working towards becoming the third largest GaN manufacturer by 2020, with sales over €100 million. The new production line development reflects OMMIC’s vision to become a dominant player in serving the 5G and satellite communications markets. A pioneer in III-V GaAs and GaN semiconductors, the French manufacturer now looks to strengthen its capability to cover the needs of 5G antenna relays at 28 and 40 GHz as well as serve and assist its current clients with more modern equipment. Its processes can be used at frequencies above 30 GHz with output powers that have not yet been achieved. With 5G expected to take off through large scale consumer adoption in 2020, OMMIC has signed partnerships with leading names like Huawei to support the development of 5G base stations. OMMIC raised funds for the construction of the leading-edge factory for III-V semiconductors 6-inch GaN production line in Europe in June 2016 through key players like Bpifrance, BNP Paribas, Banque Populaire and Financière Victoire. Read more

Comtech Xicom Technology Expands its High Power GaN SSPA Product Line Source: Everything RF

Comtech Xicom Technology, a part of Comtech's Commercial Solutions segment has released a series of high-power GaN SSPAs as part of its industry-leading SSPA product line. The new compact and rugged amplifiers are significantly more efficient than competing SSPAs making them ideal for transportable and mobile applications where power draw matters.

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For Ku-band customers, the new XTLIN-200K covers the 13.75 to 14.5 GHz Ku-band with a minimum of 200 W of linear power. The unit is available in a compact, low profile outdoor package that is ideally suited for transportable applications. The new XTLIN-100K also covers the 13.75 to 14.5 GHz, with a minimum of 100 W of linear power, and is in the same package size as its industry-leading 100 W Linear X-band unit, allowing easy conversion from X-band to Ku-band. At X-band, the new XTLIN-200X further extends Comtech Xicom’s tactical X-band product line, offering a minimum of 200 W of linear power. The compact package size is identical to that of the new 200 W Ku-band amplifier. Comtech Xicom already had industry-leading high efficiency X-band GaN products in certified terminals at linear powers of 20 W, 50 W and 100 W – and now the product line extends to 200 W. The new XTSLIN-200X compares favorably in size, weight, and especially power consumption to available products at this power level, and the common package size with the new Ku-band products is ideal for tactical military customers that want to optimize satellite availability. The Ku-band products are ideal for both commercial and military SATCOM applications, with very high efficiency that’s optimal for high data rate transportable applications. Comtech Xicom manufactures a wide variety of tube-based and solid-state power amplifiers for military and commercial satellite uplink applications. Its product range encompasses power levels from 8 W to 3 kW, with frequency coverage in sub-bands within the 2 GHz to 45 GHz spectrum. Amplifiers are also available for fixed and ground-based, ship-board, and airborne mobile applications. Read more

GaN on SiC Power Transistors for 3.5 GHz Cellular Source: Microwave Journal

The promise of 5G new radio technologies to provide significant improvements in throughput, super low latency and reliable, ubiquitous coverage is critically based on the availability of new spectrum. The 3GPPP group has identified new spectrum both below and above 6 GHz in a drive toward global harmonization. The future 5G ecosystem will most likely feature macro base stations transmitting in spectrum below 6 GHz for physical coverage, while mmWave frequencies will be used for capacity enhancements.

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The frequency band from 3400 to 3800 MHz has generated wide interest due to its potential to be available on a global basis, having already been identified for mobile communications use in many European countries, in China (which includes frequencies down to 3300 MHz) and in the U.S. RF characteristics at 3.5 GHz make this band suitable for use in both massive MIMO systems with beamforming antennas and in more traditional cellular base station architectures. ITU identifies these 3.5 GHz frequencies as band 42 (3400 to 3600 MHz) and band 43 (3600 to 3800 MHz). THREE NEW DOHERTY TRANSISTORS Many field trials are underway in the 3.5 GHz bands. To address this market, Infineon has developed a line of GaN on SiC RF power transistors for Doherty amplifier applications that are capable of the highest efficiency and broadband operation. GaN on SiC technology has stormed the cellular RF power market in recent years due to its high-power density and high efficiency. These characteristics enable designers to create highly compact amplifier circuits with more than a 10 percentage point improvement in efficiency above 3 GHz, compared to LDMOS solutions, and wideband performance that facilitates the design of Doherty amplifiers.

Figure 1 The GTRA362002FC is an asymmetric transistor delivering more than 200 W of combined peak output power.

These transistors are matched for optimal operation between 3400 and 3600 MHz, the band with the most global availability. One of the challenges at this band is the wide signal bandwidth of 200 MHz. To facilitate the design of a wideband Doherty and to compensate for the changing input impedance of the peak amplifier over power (running at class C), special attention was placed on the design of the internal transistor input match, with techniques developed to enhanced wideband operation while leaving the output unmatched. Further, these transistors use an asymmetric design for better efficiency with high peak-to-average ratio (PAR) signals. The GTRA362002FC is an asymmetric transistor with more than 200 W of combined peak output power, designed for amplifiers in 20 W cellular systems. It has two outputs: the carrier or main side with 85 W output

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power and the peak side with 115 W of P3dB output, for a split ratio of 1:4. Infineon developed a Doherty reference design that provides 14 dB of gain, 45 percent drain efficiency and ‐29 dBc adjacent channel power ratio (ACPR), measured with a single carrier WCDMA, 10 dB PAR signal at 3600 MHz and 29 W average output power (see Figure 1). The GTRA362802FC is also an asymmetric design. Offering more than 300 W of combined peak output power, it is targeted at 30 W cellular systems. It provides 115 W on the main side and 170 W on the peak side of a Doherty. With a single carrier WCDMA, 10 dB PAR signal at 3600 MHz and 44 W average output power, a Doherty amplifier reference design is capable of 14 dB of gain, 49 percent efficiency and ‐31 dBc ACPR. Typical Doherty performance of the GTRA362802FC is shown in Figure 2 (Pout, efficiency and gain) and Figure 3 (gain and efficiency versus frequency).

Figure 2 Typical Doherty output power, efficiency and gain of the GTRA362802FC at 3500 MHz. The transistor is biased at VD = 48 V, IDQ (main) = 140 mA and VGS (peak) = −5.3 V.

Figure 3 Typical Doherty gain and efficiency vs. frequency of the GTRA362802FC. The transistor bias is the same as for Fig. 2.

The higher power GTRA364002FC has been designed for use in 40 W cellular systems and provides more than 400 W of combined peak output power. Its main side outputs 170 W at P3dB and the peak side 255 W, for a 1:5 power split ratio. Using a single carrier WCDMA, 10 dB PAR signal at 3600 MHz and at 59 W average output power, the Doherty reference design is capable of 13 dB of gain, 43 percent efficiency and ‐30 dBc ACPR. All devices are available in an open cavity, ceramic lid package with CPC flange. Thermal resistance for these transistors ranges from 1 to 1.7°C/W (measured at Tcase = 75°C and CW signals using an infrared measurement). Engineering samples are available, as well as a reference Doherty amplifier for each product; volume production is planned for the end of 2017. Read more

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OTHER

LayTec ships in-situ metrology system to GaN-on-SiC customer Source: Semiconductor Today

In-situ metrology system maker LayTec AG of Berlin, Germany recently shipped a comprehensive EpiCurve TT/Pyro 400 in-situ metrology hybrid system to an industrial customer in North America. The metrology station combines automated in-situ wafer bow and film thickness measurements with two pyrometry wavelengths: near-infrared (NIR) at 950nm and near-ultraviolet (near-UV). In gallium nitride on silicon carbide (GaN-on-SiC) and gallium nitride on silicon (GaN-on-Si) metal-organic chemical vapor deposition (MOCVD) technology, the growth of sophisticated nucleation and strain management layers is essential for the quality of the material and the performance of the final devices, says LayTec. At the same time, these layers are a challenge for highly accurate wafer temperature control: IR light from other hot parts of the reactor is scattered into the NIR pyrometer and causes Fabry-Perot artifacts, affecting its precision. However, the GaN buffer specifically emits thermal radiation in the near UV and the temperature measured with Pyro 400 is not affected by the NIR thermal radiation scattered by the buried functional layers. Therefore the combination of NIR pyrometry with Pyro 400 allows precise control of the wafer temperature during the whole deposition process, says LayTec. Read more

Nitrides: Strategies to boost performance Source: CompoundSemiconductor

Presentations at the twelfth International Conference on Nitride Semiconductors offered an insight into strategies for improving the performance of UV LEDs, lasers and various forms of transistor by Jean-Yves Duboz from CRHEA-CNRS There is no doubt that a material system that has been used to manufacture countless devices for more than two decades is a success. But that does not mean that the devices have been commoditised, or that the material system is fully understood. That’s the state of affairs for GaN-based devices. While myriad LEDs and lasers have been shipped, netting billions of dollars, many questions remain that cover many bases. These questions are related to optoelectronic, RF and power devices, and to material properties and growth mechanisms. Anyone wishing to hear the latest views on any of these matters should have attended this year’s International Conference on Nitride Semiconductors, held in the historic city of Strasbourg during several rather wet days at the end of July. If they made the trip, they would have had the chance to talk to more than 800 delegates from all over the globe that met together in the Palais des Congrès et de la Musique. Many made the trip from Asia, which accounted for 43 percent of attendees, including 20 percent from Japan, while Europe contributed 42 percent and the US 12 percent. Chris Van de Walle from UCSB provided a beautiful opening talk to this biannual meeting with a didactic overview of GaN material and its specific properties. The west-coast academic championed the need for a proper reference for calculating the spontaneous polarization in nitrides – it is a key feature of these materials, and one that plays a critical role in device behaviour. Van de Walle also discussed droop, the decline in LED efficiency at high drive currents. He stressed the importance of the Auger effect, which he believes has been underestimated by many authors. In addition, he explained how non-radiative recombination on point defects can be enhanced by the excited states of defect levels.

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Echoing some of these themes in the final plenary talk on the closing day, Slatko Sitar from North Carolina State University highlighted the importance of point defects in AlGaN. These imperfections increase non-radiative recombination, leading to a reduction of UV LED efficiency. According to Sitar, it is the growth mode that governs the population of these point defects, which can take the form of either intentional or residual doping. Sitar also explained why intermediate AlGaN phases appear during the growth of AlGaN epilayers on AlN substrates. He pointed out that this low dislocation system allows the observation of a kinetically driven phase separation on the surface, which occurs due to strain. The extent of the separation depends on the temperature, growth rate and off-cut angle of the substrate. During the conference many other groups reported results rela ted to these additional AlGaN phases. However, in most cases they arose in more dislocated systems, where surface kinetics are obscured by the effect of dislocations. One of the highlights of the material session was the presentation by Bastien Bonef from UCSB, who showed both the beauty and the limitation of atom probe tomography. He argued that contrary to popular belief, atom probe tomography cannot be quantitative, unless it involves the use of a reference sample. Bonef also pointed out that the exact – and largely unknown – shape of the sample directly impacts the topology of the reconstructed profile. Another talk in this session, given by Al Balushi from Pennsylvania State University, revealed that it is possible to form a two-dimensional layer of GaN between a SiC substrate and a graphene layer obtained thereon with a migration-enhanced encapsulation method. This is a triumph for GaN, as it can now replicate what has been accomplished with its BN cousin. It is not yet clear what applications may benefit from two-dimensional GaN, but its very high bandgap of 4.8 eV suggests that it has great promise in the UV. By undertaking precise transmission electron microscopy measurements, Balushi and co-workers observed how gallium atoms intercalate between graphene and the SiC, before reacting with ammonia to form a thin GaN layer with R3m symmetry. Improvements in the visible... Although academics dominated the conference, there were plenty of presentations from those in industry. They included plenary speaker Guillaume Arthuis, President of BBRight, a French-based developer of laser projection technologies. Arthuis argued that lasers can revolutionise movie projection by lowering the power consumption compared to filtered xenon lamps. What’s more, lasers can simplify 3D projection, and by separating the light source from the digital light projector, they can yield simpler, cheaper, and more reliable systems in movie theatres. However, the downside of laser projection is speckle, stemming from the high degree of coherence of the laser. Addressing this issue is not easy – so far the best solution, which is far from ideal, is to shake the screen. Arthius will have been pleased to hear talks at the meeting describing recent improvements in visible semiconductor laser performance. Masahiro Murayama from Sony Corporation announced that the company’s green lasers can now deliver a 1 W CW output at 530 nm, under a drive current of 1 A. This laser has a wall plug efficiency of 17 percent, and an estimated lifetime of over 20,000 hours. Another pioneer of powerful green lasers is Osram Opto Semiconductors. Spokesman for that company, Harald König, told delegates that its green 517 nm lasers can now produce 120 mW at 200 mA, with a wall plug efficiency of 11 percent. Increase the wavelength to 532 nm and wall plug efficiency falls to 6.5 percent. Other developments in visible nitride emitters included impressive results on green VCSELs by a team including Xin Zhang, who is affiliated to Xiamen University. Zhang described a surface-emitting device that produced CW, room-temperature emission at 560 nm with a threshold of 780 A cm-2. Meanwhile, Czesław Skierbiszewsk, from TopGaN and the Institute of High Pressure Physics at the Polish Academy of Sciences, revealed the use of tunnel junctions in MBE-grown blue lasers. These devices demonstrated a slope efficiency of 0.85 W/A. Erin

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Young from UCSB is pursuing the same goal of improving the laser slope efficiency by introducing a tunnel junction in her blue edge-emitting lasers and VCSELs. With this modification she obtained a seven-fold increase in the power produced by the VCSEL. Moving further to the red, Yasufumi Fujiwara from Osaka University revealed that the addition of europium to the nitride quantum well enables a shift in emission to longer wavelengths. He and his co-workers fabricated red LEDs that produce 1.2 mW at 621 nm under a drive current of 20 mW. These results correspond to an external quantum efficiency of 3 percent. Higher efficiencies are possible, suggested Fujiwara, by optimising the incorporation site of europium so that it enhances energy transfer between this element and the GaN lattice. An even more exotic approach to increasing the emission wavelength of nitride materials is to incorporate antimony into the active region during MBE growth. Zetian Mi, now at Michigan University, is leading a team exploring this approach. He told delegates that incorporating just 1 percent of antimony can shift emission to 600 nm. He explained that while changes to indium content merely impact the conduction band, the addition of antimony pushes up the valence band. Confirmation of these findings could unlock the door to new designs of nitride optoelectronic devices. Other developments in visible nitride emitters included impressive results on green VCSELs by a team including Xin Zhang, who is affiliated to Xiamen University. Zhang described a surface-emitting device that produced CW, room-temperature emission at 560 nm with a threshold of 780 A cm-2. Meanwhile, Czesław Skierbiszewsk, from TopGaN and the Institute of High Pressure Physics at the Polish Academy of Sciences, revealed the use of tunnel junctions in MBE-grown blue lasers. These devices demonstrated a slope efficiency of 0.85 W/A. Erin Young from UCSB is pursuing the same goal of improving the laser slope efficiency by introducing a tunnel junction in her blue edge-emitting lasers and VCSELs. With this modification she obtained a seven-fold increase in the power produced by the VCSEL. Moving further to the red, Yasufumi Fujiwara from Osaka University revealed that the addition of europium to the nitride quantum well enables a shift in emission to longer wavelengths. He and his co-workers fabricated red LEDs that produce 1.2 mW at 621 nm under a drive current of 20 mW. These results correspond to an external quantum efficiency of 3 percent. Higher efficiencies are possible, suggested Fujiwara, by optimising the incorporation site of europium so that it enhances energy transfer between this element and the GaN lattice. An even more exotic approach to increasing the emission wavelength of nitride materials is to incorporate antimony into the active region during MBE growth. Zetian Mi, now at Michigan University, is leading a team exploring this approach. He told delegates that incorporating just 1 percent of antimony can shift emission to 600 nm. He explained that while changes to indium content merely impact the conduction band, the addition of antimony pushes up the valence band. Confirmation of these findings could unlock the door to new designs of nitride optoelectronic devices. ... and the UV The performance of nitride devices is also improving in the UV. For LEDs operating in this spectral domain, many groups are exploring the trade-off between a good light extraction, by employing a p-AlGaN contact layer, and realising good carrier injection with a p-GaN contact layer. Both options lead to a similar wall plug efficiency: it is about 10 percent at 275 nm. RIKEN chief scientist Hideki Hirayama showed that this wall plug efficiency can be achieved with an AlGaN top contact, leading to an external quantum efficiency of 20 percent. With the alternative approach of the GaN contact, results reported in recent academic literature show that although the external quantum efficiency is just 10 percent, the lower bias results in a similar wall plug efficiency. Going to even shorter wavelengths causes efficiency to plummet. According to Leo Schowalter, Chief Technology Officer at Crystal IS, efficiency halves for every shortening of wavelength by 5 nm. This rule of thumb is backed up by his report of an external quantum efficiency of about 0.3 percent at 239 nm, for a 1.8 mW LED, and the claim of a 4 percent external quantum efficiency by Akira Hirano from UV Cratftory, for a 260 nm LED.

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Modifications to the standard device architectures are producing exciting results in the UV. Zetian Mi spoke about the use of AlN nanowires, which realise extraordinarily high levels of p-type doping, thanks to strain relaxation. Using this approach, his group has produced 239 nm lasers and 207 nm LEDs. Adding a tunnel-junction is another modification that shows promise. Siddharth Rajan from The Ohio State University revealed the successes of his group with this approach, including an on-wafer wall plug efficiency of 1 percent for a 287 nm device operated at 12 V. An even more novel approach, described by Thomas Wunderer from PARC of Pan Alto, CA, is to replace electrical injection with electron-beam pumping. This approach enabled lasing action at 387 nm; and also emission at 246 nm, with a power of 230 mW, using pumping with a 4.5 mA current and a 12 kV accelerating voltage. For the shorter wavelength, wall plug efficiency is 0.4 percent. Progress in LEDs and lasers continues to be driven by a combination of experimental efforts and theoretical work – together they can lead to new insights. At this year’s ICNS, Aurélien David, Senior Principal Scientist at Soraa, gave new insights into the physics of LEDs within the framework of the well-known ABC model, which describes the various recombination mechanisms for the device. David explained that the A, B and C coefficients all depend on current, and revealed that with this modification it is possible to produce a very good fit to experimental data. Meanwhile, Gerhard Klimeck, an academic at Purdue University, explained that it is possible to correctly describe the transport in LEDs with a full quantum model that is based on a non-equilibrium Green function. When talking about nitrides, one does not necessarily think about quantum optics. However, nitrides are good candidates for fabricating true single-photon emitters working at room temperature. Good results have been obtained by Yasuhiko Arakawa’s group from the University of Tokyo. Spokesman for this team, Mark Holmes, detailed quasi perfect, single-photon emitters (g2(0)=0.02). These were obtained by working at a low temperature (10K), and by exploiting the quantum-dot like fluctuations in GaN quantum wells. Further highlights from this session that covered optical devices included: the use of LEDs in high bandwidth communication and positioning, described in a talk by Phil Dawson from the University of Manchester; a presentation from Qian Sun from Sinano detailing a CW, room-temperature laser grown on silicon, as well as photonic circuits – including an emitter, guides and detector – made with this material system; and in a similar vein, the talk by Fabrice Semond from the University Côte d’Azur, describing an optically pumped microdisk laser grown on silicon that emits from 275 nm to 470 nm. Another advance, reported by Moti Katz from Soreq NRC, Israel, was a transition at 1.8 μm associated with strong coupling. This is commonly observed with interband transitions, but in this case it resulted from intersubband transitions, observed in both transmission and in the photocurrent from a quantum cascade detector. Power devices Although GaN power devices are not generating the sales of their LED cousins today, revenues are rising, and the potential for further growth is very promising. One of the leaders of device production is Infineon Technologies, and at ICNS-12 Thomas Detzel, the firm’s Senior Manager for GaN Technology Development, closed the conference with a historical and technical comparison of the capabilities of GaN and silicon for power applications. In his plenary talk, he argued that the fundamental advantage brought by the nitrides over silicon is the combination of a lower on-state resistance (RDSON) and a negligible recovery charge. Thanks to these attributes, GaN devices can go faster while consuming less power. That does not mean, however, that silicon devices are doomed. Detzel believes that it will take some time before GaN can take significant market share in the power arena, and he expects GaN to coexist with silicon for a long time, rather than replacing the incumbent. Within the electronic session, the focus was on power electronics, and in particular established horizontal FETs and emerging vertical transistors, plus Schottky diodes. However, there were also reports on RF devices,

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including those with vertical structures. At the gathering in Strasbourg, researchers described the development of devices with classical and quantum transport. Examples of the former include finFETs pursued by Tomás Palacios’ group at MIT and fin MOSFETs fabricated by Maher Tahhan and co-workers at UCSB, while the latter includes the tunneling hot electron transistor, described by Siddharth Rajan from The Ohio State University. The talks in this session revealed two trends in nitride electronics: a move to more vertical devices; and the use of nanotechnology to provide better control of the electric field in the gate region. A group pioneering the latter is that of Elison Matioli and co-workers from EPFL. Using slanted tri-gate structures, they realised breakdown voltages of up to 1.8 kV. Another move within the power electronics community is to grow GaN devices on a native substrate. Tohru Oka from Toyoda Gosei described efforts in this direction, including the fabrication of a Schottky diode with a lateral field plate that had a breakdown voltage, at 1.8 mΩ cm-2, of 770 V. The recovery time for this diode is just 50 ns, a value far less than that for equivalents made from silicon and SiC. Oka revealed that the field played a crucial role in realising a high breakdown voltage in the MOSFET – its addition propelled the breakdown voltage from 775 V to 1600 V. However, reaching an on-resistance of just 1.8 mΩ cm-2 required a slight sacrifice to this figure. Oka and co-workers have formed switching circuits formed from the FETs and GaN Schottky diodes with a switching time of just 20 ns, and switching energies for turn-on and turn-off of 12 μJ and 90 μJ, respectively. Those attending ICNS-12 will be aware of the move to higher frequencies for applications and circuits. GaN technology could serve here: Rudiger Quay from Fraunhofer IAF and Kozo Makiyama from Fujitsu both argued that point-to-point communication at 84 GHz could benefit from this wide bandgap technology. However, José Jimenez, a Fellow of Device Physics at Qorvo, warned that GaN still suffers from a lack a linearity and a lack of reproducibility in this characteristic. In his opinion, based on existing performance, GaN has limited capability to replace GaAs. Another highlight of the electronic session was the presentation by Grace Xing from Cornell University. Xing reported convincing results on resonant tunneling diodes grown by MBE on GaN substrates. She observed clear, stable and repeatable negative differential resistance at current densities ranging from a few to 180 kA cm-2. This indicates that there is tunnel transport through fundamental and excited states in a thin GaN well in between two AlN barriers. This negative differential resistance led to oscillations at 300 MHz when the diode was inserted into a resonant circuit. In addition, impact ionization was observed, likely due to high-energy ballistic electrons crossing the outer GaN region of the structure. More reports on GaN transistors and other devices will be given at the next ICNS, held in Seattle in July 2019, and chaired by Alan Doolittle from Georgia Tech. For researchers that can’t wait that long to hear and discuss developments in the nitrides, one option is the International Workshop on Nitride Semiconductors, which will be held next year in Kanazawa, Japan, in mid-November. The Palais des Congrès et de la Musique hosted the 12th International Conference on Nitride Semiconductors. This venue, also known as the Strasbourg Convention Centre, was built in the 1970s and has undergone a major facelift in the last few years. Read more

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Reedholm signs joint marketing and support agreement with Taiwan’s STAr Technologies Source: Semiconductor Today

Reedholm Systems of Georgetown, TX, USA has signed a joint marketing and support agreement with STAr Technologies of Hsinchu City, Taiwan to provide a turn-key offering consisting of a test system, prober/handler, and load board/probe card, with characterized, assured performance of all three items. Founded in 1983, Reedholm provides new and fully refurbished parametric and wafer-level reliability (WLR) test systems, high-power wide-bandgap test systems, and support and service agreements. Established in 2000, STAr provides intellectual property, software, hardware, consumables, service and expertise to the semiconductor industry, spanning parametric electrical test (E-test), wafer-level and package-level reliability (WLR & PLR), mixed-signal tests, assembly & packaging services, probe cards, load boards, test interfaces and sockets, to top-tier players such as TSMC, UMC, Global Foundries, SMIC, KYEC, ASE, Samsung, Hynix, Elpida, Toshiba, Renesas, Maxim, and OmniVision. The combined offerings will be under the Reedholm Systems brand (regardless of where the products are sold) for activities such as: process control monitoring (PCM), wafer-level die sort, packaged part/final test, and reliability (packaged and wafer level). For the burgeoning wide-bandgap power device market, customers are demanding newly designed products with safety requirements in mind for applications that involve measuring voltages of 10kV and currents of 50A or more. Reedholm and STAr are striving to develop the supply of such tools on a broader basis and share details about evolving customer needs. Reedholm’s products include a series of parametric test systems (RI-40, RI-75, RI-EG) that are used for the gamut of dc parametric test requirements. The latest system – the RI-10kV/50A model – addresses both vertical and lateral GaN and SiC device test requirements. STAr’s range includes the Virgo series parametric and reliability probe cards, Aries series wafer-sort/function tests probe cards, and the Magic A-series, P-series and X-series Probe Station. STAr will have primary market responsibility in the Pacific Rim markets (Taiwan, Korea, China, Japan, Singapore, Malaysia, along with access to Thailand and Philippines), while Reedholm will have primary responsibility for North American markets. The parties will work together to address how to best serve customers in Europe and markets outside of North America and the Pacific Rim. Read more

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PATENT APPLICATIONS

More than 280 new patent applications were published in September 2017.

Main patent applicants Number of new patent applications

Xidian University 19

Huacan Optoelectronics 12

Toshiba 12

Fuji Electric 9

Panasonic 8 Other patent applicants: 13th Research Institute Of China Electronics Technology, Advantest, AGH University Of Science And Technology, Akoustis, Analog Devices, Anhui Core Microelectronics, Anhui Sanan Optoelectronics Technology, Asahi Kasei, Beijing Huajin Chuangwei Electronics, Boeing, British Nuosaike Technology, Cambridge Electronics, Central Glass, Chengdu Hiwafer Technology, China Electronic Technology, Chip Foundation Technology, Cornell University, Delta Electronics, Denka, Dongguan Photoelectricity Research Institute Of Peking University, East China Institute Of Technology, Enraytek Optoelectronics, Focus Lightings Science & Technology, Fudan University, Fujitsu, Gallium Semiconductor Technology, GaN Systems, GE Aviation Systems, Genesis Photonics, Global Energy Interconnection Research Institute, Guangdong Deli Photoelectric, Guangdong Institute Of Semiconductor Industrial Technology, Guangdong Midea Refrigeration Equipment, Guangdong University Of Technology, Guangxi Gao Yan Electrical Engineering Liability, HC Semitek, Hongik University Industry Academia Cooperation Foundation, Huaian Aucksun Optoelectronics Technology, Hubei University, Imec, Indian Institute Of Science, Infineon Technologies, Institute Of Microelectronics Chinese Academy Of Sciences, Institute Of Semiconductors, Intel, Jiangnan University, Jiangsu Broadwave Electronics Technology, Jiangsu University Of Science & Technology, Katod, Korea Polytechnic University Industry Academic Cooperation Foundation, Kyoto Institute Of Technology, Kyushu University Institute Of Technology, LG Innotek, Lite On Opto Technology, Meijo University, Midea, Mitsubishi Chemical, Mitsubishi Electric, Murata Manufacturing, Nagoya University, Nanchang Huanglv Lighting, Nanchang University, Nanjing Purple Branch Optoelectronics Technology, Nanjing University Of Posts & Telecommunications, Nanjing University Of Science & Technology, National Institute Of Advanced Industrial Science & Technology, National Technology & Engineering Solutions Of Sandia, No 55 Institute Of China Electronics Science & Technology, Osaka University, Osram Opto Semiconductors, RG Innovations, Shenzhen Founder Microelectronics, Sichuan University, South China Normal University, South China University Of Technology, Southeast University Nanjing, Stanley Electric, Sumitomo Electric Industries, Sun Yat Sen University, Suzhou Ruiermei Optoelectronics Technology, Suzhou University Of Science & Technology, Taiwan Semiconductor Manufacturing (TSMC), Tohoku University, Toshiba Lighting & Technology, Toshiba Memory, Toyoda Gosei, Toyota Central R&D Labs, University Beijing, University Of Electronic Science & Technology Of China, Xiangneng Hualei Optoelectronic Corppration …

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New patent applications selected by Knowmade

Reduced punchthrough breakdown in gallium-nitride transistors Publication Number: WO2017164841 Patent Applicant: Intel (USA)

There is disclosed in an example, a gallium nitride (GaN) field effect transistor (FET) having a gate, a drain, and a source, having: a doped GaN buffer layer; a first epitaxy layer above the buffer layer, the first epitaxy layer having a first doping profile (for example, doped, or p-type doping); and a second epitaxy layer above the first epitaxy layer, the second epitaxy layer having a second doping profile (for example, undoped, or n-type doping).

Single-chip high speed and high voltage level shifter Publication Number: US2017279449 Patent Applicant: Infineon Technologies Americas (USA)

A semiconductor device includes a low voltage region, a high voltage region monolithically integrated with the low voltage region in a semiconductor substrate, where the low voltage region is electrically coupled to the high voltage region through a capacitive isolation barrier, where the high voltage region is structurally isolated from the low voltage region by an isolation structure. The isolation structure includes a junction termination structure, a deep trench structure, or a reduced surface field (RESURF) structure. The isolation structure forms an isolation ring substantially enclosing the high voltage region in the semiconductor substrate. The low voltage region is configured to provide a differential signal to the high voltage region through the capacitive isolation barrier. The high voltage region is configured to receive a differential signal from the low voltage region through the capacitive isolation barrier so as to level shift the differential signal.

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System architecture for battery charger based on gan-based power devices Publication Number: US2017279287 Patent Applicant: Boeing (USA)

A system architecture for a battery charger that employs GaN-based power devices. The system takes advantage of the active power electronics circuits for power conversion, utilizing controls for power factor correction at its input and constant current/constant voltage regulation at its output. Specifically, a universal GaN-based battery charger architecture is proposed for charging either low- or high-voltage batteries using either three-phase 230-V variable frequency or three-phase 115-V constant frequency AC input power, while meeting stringent power quality and electromagnetic interference aerospace requirements.

Memory enhancing and cognitive recognition device and a manufacturing method of a neuron-related brain Publication Number: CN107169564 Patent Applicant: Nanjing University of Posts & Telecommunications (China)

The present invention discloses a method for enhancing and memory and a manufacturing method of a cognitive recognition Neurons device-related brain, the device to the base wafer to a carrier substrate is Si GaN, comprising a silicon substrate layer, a silicon substrate layer disposed on the epitaxial buffer layer, disposed on the epitaxial buffer layer on an n-GaN layer, provided on the n-GaN layer on the emitter and the collector, emitter and collector structure are the same, includes sequentially from bottom to top on the floor and connected to one of the upper deck disposed in the n-GaN layer, InGaN/GaN quantum wells, p-GaN layer and a p-electrode, respectively connected to the collector and emitter through waveguides, n-GaN layer is disposed below the cavity, allowing the photo transistor and the waveguide is suspended synaptosomal. The present invention realizes three photons to electrons or protons as an information carrier in the simulated place of neurotransmitter transport, simulates the accumulated time of the human brain, spatial and spatio-temporal mixing the accumulation well accumulating the identification effect, as a foundation for the study of complex brain memory characteristics.

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Thermal-aware finfet design Publication Number: US2017271499 Patent Applicant: Qualcomm (USA)

According to various aspects, a thermal-aware finned field-effect transistor (FinFET) may have a design that can substantially reduce hot spot temperatures and resolve other self-heating problems. More particularly, the FinFET design may use aluminum nitride (AlN) fins that can provide a main thermal exit and a source, drain, and channel formed from materials that can spread or dissipate heat, wherein AlN has a high thermal conductivity compared to silicon such that using AlN to form the fins may substantially increase heat flux to a silicon substrate relative to silicon fins. Furthermore, thermal-efficient materials may be used to form the source, drain, and channel structures to further spread heat and decrease hot spot temperatures.

GaN-on-Si semiconductor device structures for high current/ high voltage lateral GaN transistors and methods of fabrication thereof Publication Number: US2017256638 Patent Applicant: GaN Systems (Canada)

A GaN-on-Si device structure and a method of fabrication are disclosed for improved die yield and device reliability of high current/high voltage lateral GaN transistors. A plurality of conventional GaN device structures comprising GaN epi-layers are fabricated on a silicon substrate (GaN-on-Si die). After processing of on-chip interconnect layers, a trench structure is defined around each die, through the GaN epi-layers and into the silicon substrate. A trench cladding is provided on proximal sidewalls, comprising at least one of a passivation layer and a conductive metal layer. The trench cladding extends over exposed surfaces of the GaN epi-layers, over the interface region with the substrate, and also over the exposed surfaces of the interconnect layers. This structure reduces risk of propagation of dicing damage and defects or cracks in the GaN epi-layers into active device regions. A metal trench cladding acts as a barrier for electro-migration of mobile ions.

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Substrate structure, semiconductor component and method Publication Number: US9768258, DE102017105714, KR20170108870 Patent Applicant: Infineon Technologies (Austria)

In an embodiment, a substrate structure includes a support substrate, a buffer structure arranged on the support substrate, the buffer structure including an intentionally doped superlattice laminate, an unintentionally doped first Group III nitride layer arranged on the buffer structure, a second Group III nitride layer arranged on the first Group III nitride layer forming a heterojunction therebetween, and a blocking layer arranged between the heterojunction and the buffer structure. The blocking layer is configured to block charges from entering the buffer structure.

C-band high-gain GaN microwave power amplifier circuit Publication Number: CN206490651 Patent Applicant: Infineon Technologies (Austria)

The present utility model discloses a C-band high gain GaN microwave power amplifier circuitry, comprises first stage amplifying circuit is integrated in a package that, subsequent stage amplifying circuit and a power supply circuit; the first stage amplifying circuit includes a GaN power amplifier driven; subsequent stage amplifying circuit includes a GaN chip, two-stage matching circuit and bias circuit; GaN GaN chip for driving a power amplifier and the gate and drain are common to the same power source. In a confined envelope of the two-stage amplification circuit is added to the inside, so that the output of the gain is greatly improved, the interior of the C-band designs are added to an offset circuit for saving installation space of the PCB circuit package periphery valid. In addition, the internal voltage-dividing circuit can share the same two-stage amplifier circuit so that the front and back gate voltage and the same drain voltage, save PCB space.

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Resistive field structures for semiconductor devices and uses thereof Publication Number: US9761675 Patent Applicant: National Technology & Engineering Solutions of Sandia (USA)

The present disclosure relates to resistive field structures that provide improved electric field profiles when used with a semiconductor device. In particular, the resistive field structures provide a uniform electric field profile, thereby enhancing breakdown voltage and improving reliability. In example, the structure is a field cage that is configured to be resistive, in which the potential changes significantly over the distance of the cage. In another example, the structure is a resistive field plate. Using these resistive field structures, the characteristics of the electric field profile can be independently modulated from the physical parameters of the semiconductor device. Additional methods and architectures are described herein.

Bidirectional switch Publication Number: WO2017159559 Patent Applicant: Panasonic (Japan)

A bidirectional switch (100) is provided with a semiconductor element (101) and a substrate potential stabilization unit (103) that stabilizes the substrate potential of the semiconductor element (101). The substrate potential stabilization unit (103) has a first switch element (131) and a second switch element (132). When the semiconductor element (101) is in an ON state, the first switch element (131) and the second switch element (132) are both turned ON.

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