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First International Symposium on SiC Spintronics Vadstena, Sweden, 15-17 June 2015
organized by Jörg Wrachtrup Erik Janzén
Stuttgart University Linköping University
Organizing Committee: Prof. Jörg Wrachtrup, Stuttgart University, Germany, [email protected] Dr. Sang-Yun Lee (University, Stuttgart, Germany) [email protected] tel. +49 (0)711 685 65280
Prof.Erik Janzén (Linköping University, Linköping, Sweden) [email protected] tel:+46(0)13281797 mobile tel: +46 70 1918696 Prof. Nguyen-Tien Son, LiU [email protected] tel:+46(0)13282531 mobile tel: +46 70 0896969 Prof. Irina Yakimenko, LiU [email protected] tel:+46(0)13288947 mobile tel: +46 70 3789574 Eva Wibom tel:+46(0)13282427 Symposium homepage: http://www.ifm.liu.se/materialphysics/semicond/1st-sic-spintronics Symposium sponsored by The Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linköping University (AFM) The Linköping Linnaeus Initiative for Novel Functional Materials (LiLi-NFM) The Knut and Alice Wallenberg project at Linköping University: Isotopic Control for Ultimate Material Properties
List of participants: Georgy Astakhov, University of Wuerzburg, [email protected] Jean-Marie Bluet, INSA-Lyon, [email protected] Michel Bockstedte,University of Salzburg, [email protected] Martin S. Brandt, Technical University of Munich, [email protected] Stefania Castelleto, RMIT University, Melbourn, [email protected] Vladimir Dyakonov, University of Wuerzburg, [email protected]. de Alex Ellison, Norstel AB, Norrköping, [email protected] Jawad Ul Hassan, Linköping University, [email protected] Adám Gali , Wigner Research Centre for Physics, Budapest, [email protected] Andreas Gällström, Rowaco AB, Linköping, [email protected] Ivan Ivanov, Linköping University, [email protected] Viktor Ivády, Wigner Research Centre for Physics, Budapest, [email protected] Naoya Iwamoto, University of Oslo, [email protected] Erik Janzén, Linköping University, [email protected] Brett C. Johnson, University of Melbourne, Australia, [email protected] Tsunenobu Kimoto, Kyoto University, [email protected] Birgit Kallinger, Fraunhofer Institute IISB, Erlangen, [email protected] Helena Knowles, University of Cambridge, [email protected] Sang-Yun Lee, Stuttgart University, [email protected] Patrick Lenahan, Pennsylvania State University, [email protected] Norikazu Mizuochi, Osaka University, [email protected] Matthias Niethammer, Stuttgart University, [email protected] Victor A. Soltamov, Ioffe Physical-Technical Institute, [email protected] Bong-Shik Song, Sunkyunkwan University, [email protected] Nguyen Tien Son, Linköping University, [email protected] Bengt Gunnar Svensson, University of Oslo, [email protected] Caspar H van der Wal, University of Groningen, [email protected] Marina Radulaski, Stanford University, [email protected] Matthias Widmann, Stuttgart University, [email protected] Jörg Wrachtrup, Stuttgart University, [email protected] Irina Yakimenko, Linköping University, [email protected] Olger Zwier, University of Groningen, [email protected]
Programme for the First International Symposium on SiC Spintronics
Vadstena, Sweden 15-17 June 2015, Symposium will be held in Klosterhotellet, Vadstena
Monday, June 15 8:50- 9:00 Welcome Jörg Wrachtrup, Erik Janzén
Session I: Materials growth 9.00-9.30: SiC bulk growth: an overview, Alex Ellison, Norstel AB
9.30-10.00: SiC fast epi for spintronics, Jawad Ul Hassan, LiU 10.00-10.30: Improvement of silicon carbide (4H-SiC) material quality, Birgit
Kallinger 10.30-11.00: Coffee break Session II: SiC defects: an Overview
11.00-11.30: SiC Quantum Spintronics: the quest for the optimum material, Jörg Wrachtrup, Stuttgart
11.30-12.00: EPR centers in SiC: an overview, Nguyen T. Son, LiU 12.00-12.30: Optical centers in SiC: an overview, Andreas Gällström, Rowaco 12.30-13.30: Lunch Session III: Single photons, single spins and spin ensembles I
13.30-14.00: Room temperature single photon source in silicon carbide, Stefania Castelletto
14.00-14.30: Single-photon emitting diode in silicon carbide, Brett C. Johnson 14.30-15.00: Coherence and control of spins in low-dimensional solid state systems,
Helena Knowles 15.00-15.30: Coffee break Session IV: Defects I
15.30-16.00: Spin physics of vacancy-related defects in silicon carbide, Michel Bockstedte
16.00-16.30: Electron Nuclear Double Resonance study of the silicon vacancy related centres in Silicon Carbide, Victor A. Soltamov
16.30-17.00: Carbon-antisite carbon-vacancy pair in SiC revisited: Optical properties of the neutral and positive charge states, Ivan G. Ivanov
17.00-17.30 What help can we get from theory to understand Spintronics defects in SiC? (Tentative title), Adam Gali
19.00: Dinner 21.00 Guided evening tour at Vadstena Castle
Tuesday, June 16 Session V: Photonics and defects 9.00-9.30: Quantum and nonlinear photonics in silicon carbide, Marina Radulaski
9.30-10.00: SiC photonic crystal nanocavities, Bong-Shik Song 10.00-10.30: Paramagnetic color centers in SiC for spintronics and imaging, Norikazu
Mizuochi 10.30-11.00: Coffee break Session VI: Sensing
11.00-11.30: High precision angle-resolved magnetometry with uniaxial quantum centers in silicon carbide, Georgy V. Astakhov
11.30-12.00: Nano-crystalline emitters and spin defect engineering in silicon carbide, Vladimir Dyakonov
12.00-12.30: Towards the ideal in vivo biomarker using SiC QDots, Jean Marie Bluet 12.30-13.30: Lunch 13.30-15.00: Guided historical tour around the Symposium premises 15.00-15.30: Coffee break Session VII: Single photons, single spins and spin ensembles II 15.30-16.00: Coherent control of single spins in silicon carbide at room temperature,
Sang-Yun Lee 16.00-16.30: All-optical coherent population trapping with divacancy spin ensembles
in silicon carbide, Caspar H. van der Wal 16.30-17.00: Optical bleaching of divacancies in silicon carbide, Olger V.
Zwier 17.00-17.30: SiC epitaxial growth using standard chemistry (Tentative title),
Tsunenobu Kimoto 19.00: Dinner Informal discussions with refreshments after the dinner
Wednesday, June 17 Session VIII: Defects II
9.00-9.30: Control of Carbon Vacancy Defects in SiC, Tsunenobu Kimoto 9.30-10.00: Electrical characteristics of HPSI SiC substrates annealed at high
temperatures, Naoya Iwamoto 10.00-10.30: Theoretical model of the dynamic spin polarization of nuclei coupled to
paramagnetic point defects: application to nitrogen-vacancy center in diamond and divacancy in SiC, Viktor Ivády
10.30-11.00: Coffee break Session IX: Defects III 11.00-11.30: Electrical detection of magnetic resonance in Si and SiC, Martin S.
Brandt 11.30-12.00: Electrically Detected Magnetic Resonance in 4-H SiC Transistors, Pat M.
Lenahan 12.00-12.30: On the Relationship Between Near Zero-Zero Field Magnetoresistance in
SiC Devices and Electrically Detected Magnetic Resonance, Pat M. Lenahan
12.30-13.30: Lunch
14.30 Bus departure to Linköping
Posters shown during the whole symposium Coherent control of single spins in silicon carbide at room temperature, Matthias Widmann
Recent progress in SiC-studies at the University of Stuttgart, Matthias Niethammer
Titles, speakers and abstracts:
SiC crystal growth: an overview
A. Ellison, Norstel AB, Sweden.
Bulk 4H SiC single crystals for semiconductor applications are today grown from the vapor phase at temperatures above 2000 oC by mainly the Physical Vapor Deposition (seeded-sublimation) and by the High Temperature CVD techniques. The diameter (now 100 and 150mm) and the quality of SiC substrates are steadily increasing. Wafers for homoepitaxy are typically oriented 4o off-axis toward the direction and polished on the Si-face, whereas wafers for heteroepitaxy are on-axis (0001). As the growth technology has matured, the quality focus has shifted from device killing defects as micropipes (today ≤0,1 to 1 cm-2) to dislocations. Typical dislocations in state of the art SiC wafers are threading screw (pure or mixed), threading edge and basal plane dislocations. The seed quality, thermal stresses and the growth process window and stability are some of the key parameters controlling their density. Conductive n-type substrates are grown with nitrogen doping (mid 1018 - low 1019 cm-
3) whereas semi-insulating substrates require low background levels of nitrogen and boron together with controlled addition of deep levels. These can either be provided by impurities such as vanadium, or in high purity crystals, by intrinsic point defects. Depending on the growth process, these can be VSi, VC, VCVSi and VCCSi [1]. In the HTCVD technique, low nitrogen doped (mid 1014 cm-3) substrates and p-type (~1018 cm-3 aluminum doped) substrates have also been demonstrated. [1] Son N.T., et al. (2007) Phys. Rev. B 75, 155204.
SiC fast epitaxial growth for spintronics
Jawad Ul Hassan1), Robin Karhu1), Ian Booker1), Erik Sörman2), Björn Magnusson2), Ivan Ivanov1), Nguyen Tien Son1) and E. Janzén1)
1Department of Physics, Chemistry and Biology, IFM, Linköping university, Sweden
2Norstel AB, Ramshällsvägen 15 SE-602 38 Norrköping, Sweden E-mail: [email protected]
4H-SiC is a superior semiconductor material mainly intended for ultrahigh power
devices because of its wide bandgap, high breakdown electric field and high thermal conductivity. The availability of large diameter substrates and high quality epitaxial growth processes make it suitable for electronic applications. Device layer structure is normally grown on 4o off-cut substrates by hot-wall CVD technique using silane and propane as source gases. The growth rate is limited to 10 µm/h which is not suitable to grow thick layers for high voltage devices. Also the device killer extended defects like basal plane dislocations and stacking faults and low charge carrier lifetime in epilayers (< 1 µs) which is related to point defects are the main material related issues.
We have developed a fast growth rate epitaxial process on 100 mm wafers which is based on the use of Cl during the growth. The Cl is introduced during grwoth either in the form of chlorinated precursor or HCl together with silane and propane. The process is highly efficient and can produce over 100 µm thick layer in just one hour growth. It has shown extremly pure epilayers with n-type background doping of <1x1013 cm-3, stepbunching free smooth surface with roughness <1nm and high run to run reproducibility in the doping and thickness uniformity. Additionally, the epilayers are virtually free of basal plane dislocaitons and in-grown stacking faults. Charge carrier lifetime is very sensitive parameter and can be an indicative of the quality of crystal. Using Cl based high growth rate epi process we have achived 6 µs carrier lifetime compared to 1 µs obtained using standard chemistry which reflects the purity of epilayers. We will present fast expitaxial growth on 4o off-cut 4H-SiC substrtates together with material chracterization using seveal different techniques.
Improvement of silicon carbide (4H-SiC) material quality
B. Kallinger, D. Kaminzky, M. Rommel, P. Berwian, J. Friedrich
Fraunhofer-Institute for Integrated Systems and Device Technology IISB, Schottkystrasse 10, 91058 Erlangen, Germany
The Fraunhofer IISB will introduce its activities in Silicon Carbide to the Spintronic community with a special focus on its undertakings on material development and characterization. Our activities in materials development started about 10 years ago. We were improving the 4H-SiC homoepitaxial growth process in order to avoid extended defects, e.g. dislocations and stacking faults, in homoepitaxial layers. We were able to avoid device-killing defects like Basal Plane Dislocations in epilayers and explained these experimental results by appropriate models. Within the last years, the improvement of the minority carrier lifetime by reducing the point defect density has come into focus. Therefore, the influence of epigrowth parameters like, e.g. gas mixing and growth temperature, on the point defect density and carrier lifetime are investigated by using Deep Level Transient Spectroscopy (DLTS) and microwave-detected photoconductivity decay (µ-PCD). Our recent developments target on the reduction of the carbon vacancy, which is known as a lifetime-killing defect. The experimental work is completed by implementing models regarding the point defect generation / annihilation as well as the carrier lifetime measurements. Besides the materials development, the Fraunhofer IISB has been manufacturing SiC electronic devices for more than 20 years. We are producing power electronic as well as optoelectronic SiC devices in small series or prototype fabrication. The process line could be used also to fabricate spintronic prototype devices. In our presentation, we will show and discuss our recent advances in materials development and characterization as well as introduce the device processing.
SiC Quantum Spintronics: the quest for the optimal material
Jörg Wrachtrup
Physikalisches Institut and Research Center SCOPE, University Stuttgart, Pfaffenwaldring 57, 70569 Stuttgart, Germany
Abstract is not available.
EPR centers in SiC: an overview
N.T. Son and E. Janzén
Department of Physics, Chemistry and Biology Linköping University, SE-58183 Linköping, Sweden
Silicon carbide (SiC) with two isotopes having the nuclear spin I≠0 and reasonably small natural abundance (29Si: I=1/2, 4.7% natural abundance; 13C: I=1/2, 1.1%) is a very good material for electron paramagnetic resonance (EPR) studies. The difference in the natural abundance of 29Si and 13C makes it possible to distinguish between defects occupying the C and Si lattice sites via their ligand hyperfine structures, while small natural abundances result in very narrow EPR line width which enhances the resolution. This together with the availability of high-purity single crystals help to advance EPR studies of defects in SiC. So far, many intrinsic defects and impurities have been identified using EPR in combination with theoretical calculations. Among them, some are shown to be color centers, giving rise to photoluminescence in near-infrared and visible spectral regions, and can be suitable candidates for developing optically addressable single spin sources. In this presentation, an overview on EPR centers reported in SiC is given with focusing on what remains to be clarified. Suggestions are given for some defects including the Si vacancies.
Optically active deep-level defects in SiC
A. Gällström, B. Magnusson, I.G. Ivanov, E. Janzén, Linköping University
The photoluminescence and absorption of deep-level defects in SiC will be presented. There are a number of deep-level defect centers in SiC, some of which have been identified and some still unidentified. The ones that are identified are either intrinsic or related to transition metals. The optical signature of the intrinsic defects VCVSi and VSi will be discussed, as well as the unidentified intrinsic defects UD-0 and UD-4. In the case of transition metals belonging to the first row – i.e. vanadium and chromium – the number of optical centers is equal to the number of inequivalent sites. For other transition metals, for example tungsten, molybdenum and niobium, the number of optical centers do not follow the number of inequivalent sites, but rather follow either the number of hexagonal sites or the number of quasi-cubic sites. The polarization dependence, photo luminescence excitation dependence as well as temperature dependence for the commonly observed deep-level defects will be presented. Some of the most commonly observed deep-level defects can be seen in Figure 1 below.
Figure 1 Photoluminescence at low temperatures from as-grown and electron irradiated 4H-SiC samples. The signature from V, Mo, W, VCVSi, UD-0, UD-3, UD-4 and VSi are plotted on the same energy scale.
0.8 0.9 1 1.1 1.2 1.3 1.4 1.5
Photon Energy (eV)
Inten
sisty
(linea
r sca
le)
PL, T= 2-10 K
4H-SiC V
W UD-3 VCVSi
UD-0
Cr
Mo
VSi
UD-4
Room temperature Single Photon Source in Silicon Carbide
S. Castelletto1,2, Brett C. Johnson3, V. Ivady4, I D. Beke4, I. Balogh4, Z. Bodrog4, T. Ohshima5, A. Gali4
1 School of Aerospace, Mechanical and Manufacturing Engineering RMIT University, Melbourne Australia 2 Swinburne University of Technology, Centre for Micro-Photonics, Hawthorn, Australia 3Centre for Quantum Computation and Communication Technology, School of Physics, University of Melbourne, Melbourne, Victoria 3010, Australia 4Institute for Solid State Physics and Optics, Wigner Research Centre for Physics, Hungarian Academy of Sciences, P.O.B. 49, H-1525, Budapest, Hungary 5SemiConductor Analysis and Radiation Effects Group, Japan Atomic Energy Agency,1233 Watanuki, Takasaki, Gunma 370-1292, Japan, email: [email protected] We will report on recently studied optical centres in a technologically relevant wide-band gap semiconductor, such as silicon carbide (SiC). SiC harbors many paramagnetic and optical defects emitting from the UV to the near infrared, whose quantum properties were recently unraveled [1-6]. As occurred for similar diamond point defects, some of these defects could be employed to improve existing room temperature solid state quantum technologies such as single photon sources and single spin sensing-based devices, if key SiC defects could be integrated within the material present mature technology and nanofabrication. We have recently engineered via electron irradiation and identified a bright single photon emission in 4H-SiC in the visible range attributed to an intrinsic defect, known as carbon-antisite vacancy pair. Regardless its emission in the visible, its brightness surpasses single photon emission at room temperature from bulk material, promising further advances if integrated in a photonics cavity. We further explored the integration of intrinsic defects in SiC nanostructures. Whilst nanostructures in SiC are well established down to quantum dots level of 1-2nm for biomedical imaging, however their emission is mostly from the UV to green spectral region, due to surface defects or quantum confinement. We recently show the possibility to observe single photon emission in SiC nanoparticles from 3C polytype, attributed to intra-band gap defects, likely a carbon antisite [8]. Finally a novel room temperature quantum confined system demonstrated single photon emission in nanotetrapods, owing to a localized exciton due to homogenous heterostructures of 3C/4H polytypes within the nanotetrapods [9]. These results pave the way to the deployment of SiC at the nanoscale for quantum nanophotonics.
Figure 1 The advance of quantum technology requires a single photon source operating at room temperature integrated in the same material where large scalability devices are ready available. Silicon carbide is satisfying this condition. The hexagonal silicon carbide lattice has been modified to host an isolated single defect identified with an intrinsic vacancy defect, providing an extremely bright single photon emission upon optical excitation. (a) Illustration of the excited state wave-function of the identified single photon source in 4h-SiC. (b) single defects in 4h4. (c) Isolation of equivalent defects in nanoparticles of 3c-sic emitting in the red with different photo-excitation-recombination properties8. References: 1. Koehl, W. F.; Buckley, B. B.; Heremans, F. J.; Calusine, G.; Awschalom, D. D, Nature, 479 (7371), 84 -87 (2011). 2. A. L. Falk et al., Nat. Commun., 4 , 1819 (2013). 3. S. Castelletto, B.C. Johnson., N. Stavrias, A. Gali A. & T. Ohshima, Nat. Materials 13, 151-156 (2014) 4. Kraus, H. V. et al. Nat. Phys , 10 (2), 157-162 (2014). 5. Christle et al., Nature Materials 14, 160–163 (2015). 6. Widmann et al., Nat. Materials 14, 164–168 (2015). 7. S. Castelletto, B. C. Johnson, C. Zachreson, I D. Beke, I. Balogh, T. Ohshima, I. Aharonovich, A. Gali, ACS Nano, 2014, 8 (8), pp 7938–7947. 8. S. Castelletto, Z. Bodrog, A. P. Magyar, A. Gentled A. Gali, I. Aharonovich, Nanoscale, 2014, 6, 10027-10032.
Single-photon emitting diode in silicon carbide
B. C. Johnson,1 A. Lohrmann,2 N. Iwamoto,3 Z. Bodrog,4 S. Castelletto,5 T. Ohshima,3
T. J. Karle,2 S. Prawer,2 J. C. McCallum,2 A. Gali4,6
1 Centre for Quantum Computing and Communication Technology, School of Physics, University of Melbourne, Victoria 3010, Australia 2 School of Physics, The University of Melbourne, Victoria 3010, Australia 3 SemiConductor Analysis and Radiation Effects Group, Japan Atomic Energy Agency, 1233 Watanuki, Takasaki, Gunma 370-1292, Japan 4 Institute for Solid State Physics and Optics, Wigner Research Centre for Physics, Hungarian Academy of Sciences, Budapest, POB 49, H-1525, Hungary 5 School of Aerospace, Mechanical and Manufacturing Engineering, RMIT University, Melbourne, Victoria 3001, Australia. 6 Department of Atomic Physics, Budapest University of Technology and Economics, Budafokiút 8, H-1111, Budapest, Hungary, email: [email protected] Electrically driven single-photon emitting diodes (SPED) have immediate applications in quantum cryptography, quantum computation and single-photon metrology. Mature device fabrication protocols and the recent observations of single defect systems with quantum functionalities [Cas14, Chr15, Wid15] make silicon carbide (SiC) an ideal material to build such devices.
We will discuss the fabrication of bright SPEDs in 4H and 6H, n- and p-type SiC using Al or P implantation followed by a subsequent activation anneal. Single photon emitting defects are incorporated into the near-surface active device region by virtue of the high temperature activation anneal (1600oC). Their electroluminescence (EL) displays fully polarized output, excellent photon statistics (with a count rate of >300 kHz), and high stability in both continuous and pulsed modes, all at room temperature.
Low temperature single defect photoluminescence measurements reveal that the defects may be sensitive to their local environment since a variation of the zero phonon line energies of 550-750 nm is observed. We briefly discuss the atomic origin of the emitter based on ab-initio calculations.
These results provide a foundation for the possible large-scale integration of single photon sources into a broad range of emerging spintronic applications.
Figure 1. a, Schematic of the confocal set-up used to characterize the single photon emitters. It includes a Hanbury, Brown-Twiss interferometer with two single photon avalanche detectors (D1 and D2) connected to a correlation card (CC). The dichroic mirror (DM) was removed when in used in EL mode. A partial schematic of the device consisting of an Al implanted top contact is also shown. Three floating guard rings encircle the central contact to decrease the electric field at the main contacted junction. b, IV-curve of the diode. In this device, features due to shunt resistance, tunneling current, diffusion current and series resistance are indicated by the letters a-d, respectively. c, EL map of the edge region of a device. d, Room temperature EL spectrum showing the source of the background (D1 line) and the single photon emitter with a ZPL at 745 nm. e, Background corrected anti-bunching traces with g(2)(τ = 0) < 0.1 indicating excellent single photon emission characteristics. References: [Cas14] S. Castelletto, B.C. Johnson, N. Stavrias, A. Gali A. & T. Ohshima, Nat. Materials, 13, 151-156 (2014). [Chr15] D. J. Christle, A. L. Falk, P. Andrich, P. V. Klimov, J. U. Hassan, N. T. Son, E. Janźen, T. Ohshima, and D. D. Awschalom, Nat. Materials, 14, 160 (2015). [Wid15] M. Widmann, S.-Y. Lee, T. Rendler, N. T. Son, H. Fedder, S. Paik, L.-P. Yang, N. Zhao, S. Yang, Ian Booker, Andrej Denisenko, Mohammad Jamali, Seyed Ali Momenzadeh, Ilja Gerhardt, Takeshi Ohshima, Adam Gali, Erik Janzén, Jörg Wrachtrup, Nat. Materials, 14, 164 (2015).
Coherence and control of spins in low-dimensional solid state systems
Helena Knowles
University of Cambridge, UK
Physical systems with reduced dimensionality give rise to a number of interesting
electronic and optical properties and allow the probing of microscopic and mesoscopic quantum systems. 2D materials are emerging as building blocks for novel materials of complex layered designs with engineered physical properties. In 0D, electrons trapped to a single defect site of a solid state host can be used as spin-photon links and have been very successfully used as spintronic devices for quantum sensing and quantum information processing.
In the Quantum Optics and Mesoscopic Systems group we focus on investigating and exploiting such confined electronic states. Our work on more traditional systems has been pushing towards environment control and spin coherence for nanoscale magnetometry using nitrogen vacancy (NV) centres in diamond and towards enhancing the optical and spin properties of self-assembled InAs quantum dots to improve their performance as a spin-photon interface. For NV centres in nanodiamonds in particular, we showed that an understanding of the surrounding impurity bath is crucial to achieving the best performance of the sensor spin. By manipulating the bath we were able to engineer a host environment for the NV centre which mimics a fully impurity-free bulk diamond lattice. We also make use of NV nanoscale magnetometry to investigate the magnetism at the interface of the transition metal oxides LaAlO3 and SrTiO3 which emerges at low temperatures and is so far poorly understood.
In parallel, we explore the silicon-vacancy centre (SiV) in diamond which shows great promise as a spin-photon link. The investigations on the SiV centre carried out in our group have uncovered its level structure and provided evidence for spin control. We have also recently begun exploring novel 2D materials such as WSe2 for use in quantum sensing and have observed optically active localised states.
Silicon carbide provides an excellent host for localised states, and first exciting results have been published recently, including spin state control and millisecond coherence times. We plan to explore and characterise SiC defects using the techniques and expertise gained in our related experiments.
Spin physics of vacancy-related defects in silicon carbide
M. Bockstedte1,2, F. Schütz2, T. Garratt2, V. Ivády3,4, and A. Gali3,5 1FB Materialwissenschaften & Physik, Paris-Lodron University of Salzburg,
Hellbrunnerstr. 34, 5020 Salzburg, Austria 2Theor. Festkörperphysik, Friedrich-Alexander Universität Erlangen-Nürnberg,
Staudstr. 7 B2, 91058 Erlangen, Germany 3Institute for Solid State Physics and Optics, Wigner Research Centre for Physics,
Hungarian Academy of Sciences, P.O. Box 49, H-1525 Budapest, Hungary 4Institute of Physics, Loránd Eötvös University, Pázmány Péter sétány 1/A, H-1117
Budapest, Hungary 5Department of Atomic Physics, Budapest University of Technology and Economics,
Budafoki út 8., H-1111, Budapest, Hungary Corresponding author: [email protected]
The negatively charged nitrogen-vacancy center (NV) in diamond has emerged as a candidate for the implementation of a quantum bit for quantum computing. Silicon Carbide is a material with a proven technology that also fulfils necessary conditions [1] to makes it a suitable material for hosting defect based quantum computing. The di-vacancy and the silicon vacancy with high-spin ground states are good candidates for the implementation of solid state quantum bits in this material. For these defects centers coherent spin manipulation has been demonstrated [2, 3]. Optical excitation of the high-spin ground state and subsequent spin-selective recombination via yet unknown intermediate low-spin states enables spin-initialization mediated at intersystem crossings. Together with spin-dependent luminescence this provides all-optical control of the defect spins. In order to pursue optical spin manipulation in an optimal manner it is pivotal to unravel the nature of the intermediate states, the intersystem crossings and the electron-phonon interaction in the excited states. For the candidate qubit centers in 4H-SiC we address these questions theoretically in the framework of density functional theory (DFT) and a DFT-based CI-hamiltonian method. The latter approach allows to obtain the low-spin multiplet states quantitatively that are not accessible by conventional approaches in a reliable manner. As demonstrated by density functional theory [4] the di-vacancy is essentially isoelectric to the NV center in diamond. The similarities to the NV center might indicate that the same intersystem crossings from the high to the low spin state is responsible for its fluorescence signal. By DFT and a CI- method we analyze the excited state spectrum of the defects. In contrast to the current picture of the spin dynamics of the NV center in diamond, we predict that a static Jahn-Teller effect in the first excited triplet state governs an intersystem crossing both with the excited state and the ground state of the di-vacancy. The silicon vacancy is in its own class distinct from the former defects, both due to its higher spin (S=3/2) and its three almost degenerate electronic states. Experimentally observed luminescence lines can be assigned to the inequivalent defect sites corroborating the experimental findings. Owing to the spin and a stronger electron-phonon coupling in the excited state, three groups of intermediate low-spin multiplets and ISCs distinct from the NV center and the di-vacancy are predicted.
References: [1] J. R. Weber et al., PNAS 107, 8513 (2010). [2] W. F. Koehl et al., Nature 479, 84 (2011)
[3] V. A. Soltamov et al., Phys. Rev. Lett. 108 226402 (2012). [4] A. Gali, phys. status solidi (b) 248, 1337 (2011).
Electron Nuclear Double Resonance study of the silicon vacancy related centres in Silicon Carbide
Victor A. Soltamov1, Boris V. Yavkin2, Danil O. Tolmachev1, Eugene N. Mokhov1,
Roman A. Babunts1, Sergei B. Orlinskii2, and Pavel G. Baranov1
1Ioffe Physical-Technical Institute, St. Petersburg, 194021 Russia
2Kazan Federal University, Kazan, 420008 Russia
Silicon Carbide has recently been shown to be a very attractive host material for creation room temperature optically addressable spin centres with long coherence times. Particularly the optical control of the single defect spin in SiC has been realized at room temperature for the first time on the well-studied silicon vacancy defect in 4H-SiC, known as Tv2a. Generally speaking the centers of the same origin as Tv centres in 4H persist in 6H-SiC polytype as well and have been proposed to be a favorable candidates for optically pumped quantum magnetometry. Thus the family of the silicon vacancy related defects are managed to form the basis of SiC based quantum sensors and quantum spintronics. However, for successful development of the field one have to establish the proper model of these silicon vacancy related defects, because the latter determines all spin properties, such as electron decoherence arises from decoherence of the nuclear spin bath, the way of how spin density transfers to the surrounding nucleus. Basically these processes are playing the crucial role in quantum registers based on electronic and nuclear spins or quantum magnetometry. Nonetheless, the model of these centres is still contradictory. For today two possible models are under consideration. The first one postulated these centres to be the low symmetry configuration of the negatively charged silicon vacancy in the paramagnetic state with spin S = 3/2 (VSi –). According to the second model these centres are the negatively charged silicon vacancy in the paramagnetic state with spin S = 3/2, perturbed by neutral carbon vacancies in not paramagnetic state, VC
0, located on the c axis of the crystal relatively to the silicon vacancy. According to our data obtained by means of Electron Nuclear Double Resonance we provide the strong evidence in favor to the second model. The work was supported by the Ministry of Science and Education of Russia № RFMEFI60414X0083.
Carbon-antisite carbon-vacancy pair in SiC revisited: Optical properties of the neutral and positive charge states
I. G. Ivanov1), A. Gällström1), B. Magnusson1) , N. T. Son1) , T. Ohshima2) , E. Janzén1) 1) Department of Physics, Chemistry and Biology Linköping University, Sweden 2) Japan Atomic Energy Agency, Takasaki, Gunma 370-1292, Japan Intrinsic defects in SiC have attracted recently much interest from point of view of their potential for use as quantum bits [1] and single-photon sources [2]. The carbon-vacancy carbon-antisite pair (VCCSi) has received special attention, since it has been shown to act as single-photon emitters with excellent brightness in semi-insulating (SI) 4H-SiC electron-irradiated with low doses [2]. The photoluminescence (PL) from VCCSi in the positive charge state (VCCSi+) studied in [2] appears in the visible (~645 – 680 nm, cf. Fig. 1) as sharp, so-called AB-lines at low temperatures (~80 K), but persists also as a broader band even at room temperature. Early studies [3] have associated a set of lines appearing in the infrared region (around 1200 nm, photon energies ~1 – 1.05 eV, cf. Fig. 2) with VCCSi in the double-positive charge state (VCCSi++), in order to associate the PL lines with a centre observed in electron paramagnetic resonance (EPR), the so-called P6/P7 centre. In our work, we show that in fact the most probable candidate for explaining the luminescence in the region ~1 – 1.05 eV is the pair in its neutral charge state, VCCSi0. We have studied also the positively-charged state (the PL lines reported in [2]) and show that the assignment made in [2] for some of the lines needs revision. Our assignment of the PL lines in the region ~1 – 1.05 eV to VCCSi0 is based on recent theoretical results [4] showing that the experimental photon energies and the energy separations between the PL lines associated with the four inequivalent configurations of VCCSi in 4H-SiC are in reasonable agreement with theory. We present also a physical model, which shows that the neutral VCCSi0 pair acts as a deep donor capable of binding excitons, and the observed luminescence can be explained entirely in terms of bound-exciton recombination at the defect. On the contrary, when this physical model is extended to the properties of the VCCSi+ centre, there exist two possibilities to explain the luminescence lines observed in [2]. One of them can be seen as internal transition within the centre, whereas the other can also be considered as bound-exciton recombination, in analogy with VCCSi0. Group-theoretical analysis in the frame of our physical model sheds light on the splitting of the excited states observed experimentally for VCCSi0 and, when applied to VCCSi+, allows us to distinguish between the two cases mentioned above. Results from PL and absorption studies of multiple samples with different Fermi-level positions allowing the observation of both the neutral and the positive charge states will be presented. Further evidence for the identification of the PL signatures of both VCCSi0 and VCCSi+ comes from photoexcitation of these two centres with different laser wavelengths (not shown). In particular, we show that excitation with photon energies below or above half the bandgap of 4H-SiC combined with (or, also, without) above-band gap excitation can be very useful in connecting the optical signatures of the same defect in different charge states.
References: [1] W.F. Koehl et al., Nature 479, 84 (2011). [2] S. Castelletto et al., Nat. Mat. 13, 151 (2014). [3] Th. Lingner et al., Phys. Rev. B 64, 245212 (2001). [4] K. Szász et al., Phys. Rev. B 91, 121201(R) (2015).
Figure 1. PL spectra of two different p-type 4H-SiC samples showing the VCCSi+ related AB-lines at two different temperatures, as denoted for each curve. The notations for the AB-lines follow those of reference [2]. The asterisk denotes a peak from unknown defect in the proximity of the A2, hindering its observation in sample 1. All spectra are excited with 532 nm laser. Note the vertical scale changes.
Figure 2. (a) Absorption, and (b) PL spectra of the same n-type 4H-SiC sample showing contribution from both UD-2 and VCCSi0. The sample shows strong absorption due to VCCSi0, but the contribution of the latter to the PL spectrum is mainly via appearance of absorption lines in the background emission due to UD-2. (c) PL of another n-type 4H-SiC sample showing sharp luminescence lines from both UD-2 and VCCSi0.
What help can we get from theory to understand Spintronics defects
in SiC
Adam Gali
Institute for Solid State Physics and Optics, Wigner Research Centre for Physics, Hungarian Academy of Sciences, Budapest, Hungary
Abstact is not available
Quantum and Nonlinear Photonics in Silicon Carbide
Marina Radulaski,1 Jingyuan Linda Zhang,1 Kai Mueller,1 Konstantinos G. Lagoudakis,1 Thomas M. Babinec,1 Kassem Alassaad,2 Gabriel Ferro2 and
Jelena Vuckovic1
1E. L. Ginzton Laboratory, Stanford University, Stanford, CA 94305, USA 2Laboratorie des Multimateriaux et Interfaces, Universite de Lyon, Villeurbanne
Cedex, France, [email protected]
Silicon carbide (SiC) is an emerging photonics semiconductor, which encompasses the key properties of optics materials–such as silicon, gallium arsenide, and diamond–in a single CMOS compatible platform. The high index confines light to small volumes, the wide band gap facilitates low-absorption visible photonics, the lattice symmetry provides significant χ(2) nonlinearity for efficient frequency conversion, and color centers active up to room temperatures open up opportunity for single and multi-emitter quantum photonics. We study silicon carbide photonics in CVD grown 3C-SiC on Si, with applications in nonlinear optics and cavity quantum electrodynamics based on an ensemble of color centers. We develop two electron beam lithography nanofabrication techniques, suitable for hole-based structures such as photonic crystal cavities, and pillar based structures such as microdisks and nanowires. We design, fabricate and characterize high quality factor (Q~1,000) small mode volume (V~0.75(λ/n)3) photonic crystal cavities, with tunable resonances across a telecommunications range 1,250-1,600 nm [1]. We design and fabricate smallest to date 3C-SiC microdisk resonators, with ~2 µm diameters and whispering gallery modes with quality factors up to 2,300, suitable for visible photonics. In these structures, we observe room temperature coupling between whispering gallery modes and the intrinsic emission in 3C-SiC at 600-950 nm [2]. We also explore hybrid SiC-diamond photonics using single crystal nano-diamond with silicon vacancy color centers grown on SiC substrates and devices. We model multi-emitter cavity quantum electrodynamics based on an ensemble of E-line emitters in the developed 3C-SiC microdisks, with the goal of achieving strong coupling and Ultrafast high-contrast optical switching [3]. Finally, we model nonlinear frequency conversion from infrared to visible wavelengths based on quasi-phasematched second harmonic generation in the microdisks.
References: [1] Marina Radulaski, et al , “Photonic Crystal Cavities in Cubic Polytype Silicon Carbide Films,” Optics Express Vol. 21, 26, pp. 32623-32629 (2013). [2] Marina Radulaski, et al , “Visible Photoluminescence from Cubic (3C) Silicon Carbide Microdisks Coupled to High Quality Whispering Gallery Modes.” ACS Photonics 2, 14-19 (2015). [3] Arka Majumdar, et al , “All Optical Switching With a Single Quantum Dot Strongly Coupled to a Photonic Crystal Cavity,” IEEE Journal of Selected Topics in Quantum Electronics Vol 18, pp. 1812-1817 (2012).
SiC photonic crystal nanocavities
Bong-Shik Song1,2, Seungwoo Jeon1, Yuki Yamaguchi1, Takashi Asano1, and Susumu Noda1
1Department of Electronic Science and Engineering, Kyoto University, Kyoto 615-8510, Japan 2School of Electronic and Electrical Engineering, Sungkyunkwan University, Suwon 440-746, Korea
Photonic crystal nanocavities, which can confine strongly photons in a few cubic wavelengths, have been studied much for scientific and engineering applications such as slowing and stopping lights, strong couplings, and ultra-small and integrated photonic chips [1, 2]. Until now, the conventional material of silcon (Si) has been employed mainly for realization of photonic crystal nanocavities because of its transparency at telecommunication wavelengths and the advanced fabrication techniques. However, Si-based photonic crystal nanocavities have encountered some serious limitations such as the optical loss due to an undesired the nonlinear phenomenon of two photon absorption (TPA) [3] and thermal instability due to a large thermo-optic coefficient. Furthermore, the operating wavelengths of these devices have been limited at telecommunication ranges.
In this symposium, we present our development of silicon carbide (SiC)-based photonic crystal nanocavities [4] and address above issues by employing the SiC properties of a large electronic band gap and thermal stability, in detail complete inhibition of TPA in photonic crystal nanocavities [5], ultra-broad band operation from visible wavelengths to the infrared regions [6] , and stable operating wavelengths at temperature changes [7]. In addition, we demonstrate multiple-channel wavelength conversions of second harmonic (SHG) and sum frequency generations (SFG) in a SiC photonic crystal nanocavity [8, 9]. These results will pave the way for opening SiC photonics and lead to promising quantum applications by employing unique states of the SiC material [10].
References: [1]B. S. Song, S. Noda, T. Asano, and Y. Akahane, Nat. Mater. 4, 207 (2005) [2]Y. Sato, Y. Tanaka, J. Upham, Y. Takahashi, T. Asano, and S. Noda, Nat. Photonics 6, 56 (2012). [3]Y. Uesugi, B. S. Song,T. Asano, S. Noda, Opt. Express 14, 377 (2006). [4]B. S.Song, S. Yamada, B. S. Song, T. Asano, and S. Noda, Opt. Express 19, 11084 (2011) [5]S. Yamada, B. S. Song, J. Upham, T. Asano,Y. Tanaka, and S. Noda, Opt. Express 20, 14789 (2012) [6]S. Yamada, B. S. Song, T. Asano, and S. Noda, Appl. Phys. Lett. 99, 20 (2011). [7]S. Yamada, B. S. Song, T. Asano, and S. Noda, Opt. Lett. 36, 3981 (2011). [8]S. Yamada, B. S. Song, S. Jeon, J. Upham, Y. Tanaka, T. Asano, and S. Noda, Opt. Lett. 39, 1768 (2014). [9]S. Jeon, B. S. Song, S. Yamada, Y. Yamaguchi, J. Upham, T. Asano, and S. Noda, Opt. Express 23, 4524 (2015) [10] M. Widmann, S. Lee, T. Rendler, N. T. Son, H. Fedder, S. Paik, L.Yang, N.
Zhao, S. Yang, I. Booker, A. Denisenko, M. Jamali, S. A. Momenzadeh, I. Gerhardt, T. Ohshima, A. Gali, E. Janzén, and J. Wrachtrup, Nat. Mater. 14. 164 (2015).
Paramagnetic color centers in SiC for spintronics and imaging
Norikazu Mizuochi
Graduate School of Engineering Science, Osaka University 1-3, Machikane-yama, Toyonaka-city, Osaka, 560-8531, JAPAN
Email: [email protected]
Previously, we coheretly controled electron spin of paramagnetic color centers in SiC for the first time at room temperature. [1] Recently, interests for using SiC defects for spintronics applications is rapidly growing and the single centers were observed optically and coheret control of single spins were reported in SiC. On the other hand, recently, we have investigated on NV center in diamond. Particularly, we have interests on centers in small particles and electrical control of the quantum device such as single photon emitter [2] and spintronics device. We would like to show recent our researches on NV center in diamond and color centers in SiC and would like to discuss the future direction.
References: [1] N. Mizuochi, et al., Phys. Rev. B, 66, 235202 (2002). [2] N. Mizuochi, et al., Nature Photonics, 6, 299 (2012).
High precision angle-resolved magnetometry with uniaxial quantum centers in silicon carbide
G. V. Astakhov1, D. Simin1, F. Fuchs1, H. Kraus1, A. Sperlich1, P. G. Baranov2, V. Dyakonov1
1 Julius-Maximilian University of Würzburg, Würzburg, Germany 2 A. F. Ioffe Physical-Technical Institute, Saint-Petersburg, Russia
E-mail: [email protected]
Silicon carbide boasts a variety of quantum center types, which can be put to good use in different application scenarios: The silicon vacancies are uniaxial color centers, and – using optically detected magnetic resonance (ODMR) – can be applied to directly measure strength of an external magnetic field [1]. Here, we demonstrate that silicon vacancies can also be used to measure the orientation of the external magnetic field with respect to the defect axis with high precision [2]. The method is based on the optical detection of multiple spin resonances in the silicon vacancy defect with quadruplet ground state and suggests significant improvement of the angle sensitivity. As a probe, we use the V2 silicon vacancy in 4H-SiC and perform demonstrative experiments in a weak magnetic field of 0.5 mT. In such a weak magnetic field, its orientation is not resolved within one second integration time using a nonlinear shift of the ODMR frequencies, as initially suggested for spin-1 system [3]. But exploiting the properties inherent to spin-3/2 system, the polar angle resolution of about one degree per Hz1/2 is demonstrated in sub-millitesla magnetic fields. Our approach is suitable for ensemble as well as for single spin-3/2 color centers, allowing for angle-resolved magnetometry on the nanoscale at ambient conditions. References: [1] H. Kraus, et al., Sci. Rep. 4, 5303 (2014). [2] D. Simin et al., arXiv:1505.00176.
Nano-crystalline emitters and spin defect engineering in silicon carbide
V. Dyakonov1, F. Fuchs1, A. Muzha1, N. V. Tarakina3, D. Simin1, V. A. Soltamov2, E. N. Mokhov2, P. G. Baranov2, A. Krüger1, M. Trupke3, B. Stender1, J. Pflaum1,
G. V. Astakhov1
1 Julius-Maximilian University of Würzburg, Würzburg, Germany 2 A. F. Ioffe Physical-Technical Institute, Saint-Petersburg, Russia 3 Vienna Center for Quantum Science and Technology, TU Wien
E-mail: [email protected]
The unification of luminescent markers for bioimaging and spin centers for sensing is challenging; especially when aiming for the ideal NIR window, stability and non-toxicity. Bulk silicon carbide (SiC) is an attractive candidate despite its large band gap, which we could mitigate by the introduction of silicon vacancy defects—exhibiting NIR emission—via neutron irradiation. With a milling procedure, we fabricated SiC nanocrystals ranging from 600nm down to 60nm in size, with a further fragmentation of the latter into ca. 10-nm-size clusters of high crystalline quality separated by amorphous partitions. The luminescence of the vacancies persists in all size fractions, moreover, we were able to detect room-temperature spin resonance in these nanocrystals. [1] This may lead to new perspectives: defects in nanocrystalline SiC, as in-vivo luminescent markers, magnetic field or temperature sensors. With these and others spin-based quantum applications in mind, one main challenge is to thoroughly create, isolate, and control the defects. Here, we report defect engineering of VSi defects in SiC by means of neutron irradiation. [2] Our photoluminescence measurements show that the defect density is well controllable via the irradiation dose. The irradiation flux has been varied over 10 orders of magnitude, from 108 to 1018 neutrons/cm2. Two specific cases are of interest and will be discussed. The generation of the maximum VSi concentration without destroying the crystal structure and creation of very few, or even single isolated defects for the realization of single photon sources. References: [1] A. Muzha et al.: Appl. Phys. Lett. 105, 243112 (2014). [2] Fuchs et al.: Nat. Comms. (accepted) (2015); arXiv:1407.7065
Towards the ideal in vivo biomarker using SiC QDots
J.M. Bluet
Institut des Nanotechnologies de Lyon, INSA-Lyon, UMR CNRS 5270, Université de Lyon, 7 avenue Jean Capelle, 69621 Villeurbanne Cedex, France.
The main properties expected from a semiconductor QDot for cell labelling are biocompatibility or at least no cytotoxicity, small size (< 50nm) and strong and stable fluorescence emission. Results on SiC QDots will be presented showing that the two first criteria are fulfilled [1], but that the third one necessitates improvements. Indeed, the absolute quantum yield (<10%) for the near band edge fluorescence in SiC QDots may be too poor for specific bio application requiring low marker concentration or short collection time like dynamic marker tracking. Toward this end, strong fluorescence enhancement was achieved using plasmonic coupling in core-shell Au/SiO2/SiC system [2]. Furthermore, two photon absorption and second harmonic generation experiments demonstrate the strong non linear optical properties of SiC QDots [3] allowing two colors labelling and fluorescence emission in the skin transparency wavelength range. To go further, in the quest of an ideal in vivo biomarker, additional requirements have to be considered such as both excitation and emission in the near infrared range and paramagnetic properties for NMR tracking. Toward this end, an ab initio study has shown the potential of color centers in ultra-small (1-2nm) 3C-SiC QDots [4]. Experimental results on fabrication by chemical etching and characterization (TEM, DLS, Fluorescence) of SiC QDots with diameter < 2nm will be shown. References: [1] J.M. Bluet, J. Botsoa, Y. Zakharko, A. Geloen, S. Alekseev, O. Marty, B. Mognetti, S. Patskovsky, D. Rioux, V. Lysenko ; SiC as a Biocompatible Marker for Cell Labeling, Silicon Carbide Biotechnology: A Biocompatible Semiconductor for Advanced Biomedical Devices and Applications, p.377, Elsevier Science (2011) [2] N. Sui, V. Monnier, Yu. Zakharko, Y. Chevolot, S. Alekseev, J.M. Bluet, V. Lysenko, E.Souteyrand ; Fluorescent (Au@SiO2)SiC nanohybrids: influence of gold nanoparticle diameter and SiC nanoparticles surface density, Plasmonics 8(1), 85-92 (2013). [3]http://apps.webofknowledge.com/OneClickSearch.do?product=UA&search_mode=OneClickSearch&excludeEventConfig=ExcludeIfFromFullRecPage&SID=P1kWEsfXzSlDSgTUO6N&field=AU&value=Zakharko, Y. Zakharko, T. Nychyporuk, L. Bonacina, M. Lemiti, V. Lysenko ; Plasmon-enhanced nonlinear optical properties of SiC nanoparticles, Nanotechnology 24(5), 055703 (2013) [4] B. Somogyi, V. Zolyomi, and A. Gali; Near-infrared luminescent cubic silicon carbide nanocrystals for in vivo biomarker applications: an ab initio study, Nanoscale 4(24), 7720-7726 (2012).
Coherent control of single spins in silicon carbide at room temperature
Matthias Widmann1, Sang-Yun Lee1, Torsten Rendler1, Nguyen Tien Son2, Helmut Fedder1, Seoyoung Paik1, Li-Ping Yang3, Nan Zhao3, Sen Yang1, Ian Booker2, Andrej Denisenko1, Mohammad Jamali1, Seyed Ali Momenzadeh1, Ilja Gerhardt1, Takeshi Ohshima4, Adam Gali5,6, Erik Janzén2, Jörg Wrachtrup1
1. Physikalisches Institut and Research Center SCOPE, University Stuttgart, Pfaffenwaldring 57, 70569 Stuttgart, Germany
2. Department of Physics, Chemistry and Biology, Linköping University, SE-58183 Linköping, Sweden
3. Beijing Computational Science Research Center, Beijing 100084, China
4. Japan Atomic Energy Agency, Takasaki, Gunma 370-1292, Japan
5. Wigner Research Centre for Physics, Hungarian Academy of Sciences, P.O. Box 49, H-1525, Budapest, Hungary
6. Department of Atomic Physics, Budapest University of Technology and Economics, Budafoki út 8, H-1111, Budapest, Hungary
Spins in solids, when well isolated from environmental spin noise sources, can serve as a two-level quantum system. This is useful for quantum information processing (QIP) [1], and quantum metrology [2]. Such applications are possible thanks to their large spin signal, the tunable quantum properties by external magnetic and electric field, and the easiness in the fabrication of their host material. One of the well-known examples is the nitrogen-vacancy (NV) center in diamond. Researchers have proven that these centers can be used as a quantum bit for QIP [3] and single spin magnetic field sensors operating at ambient conditions with the outstanding sensitivity approaching single proton sensitivity [2]. Another similar quantum system, silicon vacancies (VSi) in silicon carbide (SiC) also recently has attracted a great amount of attention especially because of the electrical properties of the host material which is easily tunable and stands out that of the diamond. Its wide bandgap which allows broadband optical access across the visible to infrared, is also useful for nanophotonics [4]. In order to test whether the creation of isolated defects in SiC is possible, we created isolated VSi defects in a pure SiC single crystal sample by 2 MeV electron irradiation. As a next step to test whether the single spin detection at room temperature is feasible, we detected the ODMR spectra of single VSi. We also found a slow dephasing rate (T2>160 µs) of single electron spins of VSi at room temperature. Our theoretical work for the single electron spin decoherence in SiC nuclear spin bath [5] tells that the mutual interaction between the nuclear spins of 29Si and 13C, the most abundant nuclei
in SiC, is drastically suppressed when they experience a big mismatch between their Zeeman levels by an external magnetic field. In addition, the smaller gyromagnetic ratio of 29Si and the larger bond length in SiC lattice lower the effective nuclear spin bath concentration thus allow long T2, even longer than that of the NV centers in isotopically purified diamond (∼500 µs). This expectation is supported by both our room temperature observation and a recent study by Christle et al., reporting a 1 ms long T2 of an electronic spin ensemble at cryogenic temperature [6]. Our results show that SiC can host single-point defects with long spin coherence times, making it promising for long-lived quantum bits and quantum metrology [6,7]. The mature fabrication methods originating from the modern silicon technology, may allow scalable spintronic devices, resembling modern electronics devices. In addition, we also explore the spin Hamiltonian of VSi in SiC (S=3/2) to discuss how to make use of S=3/2 spin systems as a vector magnetometer [8], and the origin for the unresolved finesturcture of electron spin resonance of VSi in SiC at low magnetic field [7]. We also present fabrication of SiC p-i-n diode structures for investigating electrical control of fluorescence of defects in SiC. References: [1] J. J. L. Morton and B. W. Lovett, Annu. Rev. Condens. Matter Phys. 2, 189 (2011). [2] R. Schirhagl, et al., Rev. Phys. Chem. 65, 83 (2014). [3] L. Childress and R. Hanson, MRS Bull. 38, 134 (2013). [4] B.-S. Song, et al., Opt. Express 19, 11084–11089 (2011). [5] L.-P. Yang, et al., Phys. Rev. B 90, 241203 (2014). [6] D. J. Christle, et al., Nat Mater 14, 160 (2015). [7] M. Widmann, et al., Nat Mater 14, 164 (2015). [8] S.-Y. Lee, M. Niethammer, and J. Wrachtrup, arXiv1505.06914 (2015).
All-optical coherent population trapping with divacancy spin ensembles in silicon carbide
Caspar H. van der Wal1, Olger V. Zwier1, Xu Yang1, Danny O'Shea1, Alexander R.
Onur1, Erik Janzén2, and Nguyen T. Son2
1 Zernike Institute for Advanced Materials, University of Groningen, The Netherlands
2 Department of Physics, Chemistry and Biology, Linköping University, Sweden
Divacancy defects in silicon carbide have long-lived electronic spin states and sharp optical transitions, with properties that are similar to the nitrogen-vacancy defect in diamond. If ensembles of such spins can be all-optically manipulated, they make compelling candidate systems for quantum-enhanced memory, communication, and sensing applications. We report experiments on 4H-SiC that investigate all-optical addressing of divacancy spin states with the zero-phonon-line transitions. Our magneto-spectroscopy results fully identify the spin S=1 structure of the ground and excited state (Fig. 1a), and we use this for tuning of transition dipole moments between particular spin levels. We also identify a role for relaxation via intersystem crossing. Building on these results, we demonstrate coherent population trapping (CPT, a key effect for quantum state transfer between spins and photons) for divacancy sub-ensembles along particular crystal axes [1]. Notably, weak-magnetic-field tuning of the spin states allows for controlling CPT with two lasers, without using a third laser for avoiding optical pumping into one of the three S=1 spin levels. Our initial results used photo-luminescence signals from samples with low divacancy concentration [1]. In more recent work we studied samples with 1000 times higher divacancy concentration (after electron irradiation and subsequent annealing). This allowed for CPT studies via optical transmission signals, thus directly testing electromagnetically induced transparency (EIT) in this medium (Fig. 1b). These results, combined with the availability of mature device processing technology, put SiC at the forefront of quantum information science in the solid state.
Figure 1: a) Photo-luminescence signals from two-laser magneto-spectroscopy reveal the homogeneous optical linewidth of spin-selective transitions and the structure of the spin S=1 Hamiltonians. b) Two EIT peaks (from two different combinations of ground-state spin levels) observed in the transmission of a probe laser in two-laser spectroscopy. Tuning of the strength and direction of the weak magnetic field can give a single EIT peak with near unity transmission. References: [1] O.V. Zwier, D. O'Shea, A. R. Onur, and C. H. van der Wal, Scientific Reports (NPG) 5, 10931 (2015); doi:10.1038/srep10931; arXiv:1411.1366.
Optical bleaching of divacancies in silicon carbide
Olger V. Zwier1, Xu Yang1, Danny O'Shea1, Alexander R. Onur1, Erik Janzén2, Nguyen T. Son2, and Caspar H. van der Wal1
1 Zernike Institute for Advanced Materials, University of Groningen, The Netherlands
2 Department of Physics, Chemistry and Biology, Linköping University, Sweden
When optically exciting neutral divacancies in SiC, they can change their charge state and become off-resonant with the applied laser fields. This is an effect known as optical bleaching and has been shown to occur as well in the closely related system of NV centers in diamond [1]. Though the probability per optical cycle for a divacancy to bleach is small enough to not greatly hamper coherent experiments on neutral divacancies [2], it will eventually (in the order of seconds) cause the divacancy to end up in an off-resonant state, where they can remain for a very long time (hours). To make optical quantum information applications feasible for divacancies in SiC, a good understanding of bleaching is required, including ways to prevent and undo it, which should interfere as little as possible with the intended application.
We have investigated the bleaching of several distinct divacancy ensembles in 4H-SiC, finding a mechanism of bleaching and un-bleaching (called repumping), again similar to that found in NV centers in diamond. However, the zero-phonon line (ZPL) of the bleached state is found not to lie in the band gap. This causes the repumping mechanism to be very efficient compared to the bleaching (single- versus double-photon process), making it relatively straightforward to keep divacancies in SiC in the neutral charge state. Additionally, we explore possibilities to utilize bleaching to counter inhomogeneous broadening of the ZPL, paving the way for quantum information applications realized with the spin states of fully homogeneous, unidirectional divacancy ensembles in SiC [2]. References: [1] K. Beha, N. B. Manson, R. Bratschitsch, and A. Leiternstorfer, Physics Review Letters 109, 097404 (2012). [2] O. V. Zwier, D. O'Shea, A. R. Onur, and C. H. van der Wal,
Scientific Reports (NPG) 5, 10931 (2015); doi:10.1038/srep10931; arXiv:1411.1366.
SiC epitaxial growth using standard chemistry
Tsunenobu Kimoto
Dept. of Electronic Sci. & Eng., Kyoto University, Nishikyo, Kyoto 615-8510,
Japan
Abstract is not available
Control of Carbon Vacancy Defects in SiC
T. Kimoto, K. Kawahara, B. Zippelius, T. Hiyoshi
Dept. of Electronic Sci. & Eng., Kyoto University, Nishikyo, Kyoto 615-8510, Japan
A carbon vacancy is one of the most abundant point defects in SiC (as-grown, irradiated, annealed) and of technological importance because the acceptor-like level of a carbon monovacancy works as the major carrier-lifetime killer, at least, in n-type 4H-SiC [1,2]. In this paper, understanding and control of the carbon vacancy (VC) defects in SiC are reviewed. Generation of VC defects (1) High-temperature processes, growth or annealing, induce spontaneous generation
of the VC defects. For example, the VC density in SiC epilayers grown with a fixed C/Si ratio exponentially increases with increasing the growth temperature. In a similar way, when SiC epilayers with very low VC density (< 1012 cm-3) are annealed in Ar at different temperatures, the VC density exponentially increases with temperature [3]. The authors suggest that this trend follows the equilibrium density of VC defects in SiC.
(2) The VC density is increased by irradiation of high-energy particles: Implantation of any kinds of ions, dry etching, neutron irradiation, and electron irradiation lead to significant increase of the defect. Among these, low-energy (120-200 keV) electron irradiation is an attractive process to precisely control the VC density (It can be controlled from 1012 cm-3 to 1016 cm-3), which can be employed for lifetime control.
Elimination of VC defects (1) Carbon ion implantation and subsequent annealing at 1600-1700°C is an effective
way to eliminate the VC defects (< 1×1011 cm-3) [4]. A portion of implanted C atoms diffuse into the bulk region and fill VC defects.
(2) The VC defects can be also eliminated by thermal oxidation [5]. Oxidation at higher temperature and longer time is effective for defect elimination. During oxidation of SiC, excess Si and C atoms are emitted into SiC and diffuse into the bulk region, as in the case of carbon implantation. The depth the VC-free region can be well predicted by a carbon-diffusion model [6] and it can reach over 200 µm.
The carrier lifetime can be improved from 1-2 µs (as-grown) to over 40 µs by
elimination of VC defects. Carrier recombination in such materials is also discussed. References:
[1] K. Danno et al., Appl. Phys. Lett. 90, 202109 (2007).
[2] N.T. Son et al., Phys. Rev. Lett. 109,187603 (2012). [3] B. Zippelius et al., J. Appl. Phys. 111, 033515 (2012). [4] L. Storasta et al., Appl. Phys. Lett. 90, 062116 (2007). [5] T. Hiyoshi et al., Appl. Phys. Exp. 2, 041101 (2009). [6] K. Kawahara et al., J. Appl. Phys. 111, 053710 (2012).
Electrical characteristics of HPSI SiC substrates annealed at high temperatures
N. Iwamoto1*, A. Azarov1, T. Ohshima2, A. M. Moe3, B. G. Svensson1
1 University of Oslo, Department of Physics/Center for Materials Science and Nanotechnology, PO Box 1048 Blindern, N-0316 Oslo, Norway
2 Japan Atomic Energy Agency, 1233 Watanuki, Takasaki, 370-1292 Gunma, Japan 3 Washington Mills AS, N-7300 Orkanger, Norway
Isolated point defects in high purity SiC crystals have been recognized to have capabilities required for a single photon source or a quantum bit for the future applications of quantum communication and computation technologies [1-3]. In order to realize such applications, the point defects must be integrated in electronic devices so that the point defects can be driven electrically. For SiC device fabrication, high temperature processes above 1500 °C are often required. In this work, high temperature annealing effects on the electrical characteristics of high purity semi-insulating (HPSI) SiC substrates have been studied. The material investigated is commercially available 4H-SiC HPSI substrates annealed at 1400-1700 °C, and Schottky barrier diodes were fabricated for electrical measurements. Current-voltage and admittance spectroscopy (AS) data measured above 500 K imply the presence of a midgap level (XMID) in the substrates annealed below 1500 °C. As the anneal temperature increases to 1700 °C, the XMID level seems to be eliminated and the SI characteristics of the substrates disappear. The annealed substrates become more conductive toward p-type and the shallow boron acceptor level is detectable by AS in 1600 and 1700 °C annealed substrates. In conclusion, the XMID level plays a decisive role to determine SI characteristics of the substrates since it compensates the boron acceptor level. High temperature treatments have a risk of eliminating the XMID level and the SI characteristics, and one has to be aware of this behavior if the SI characteristics are needed for the device applications. References: [1] S. Castellotto et al., Nature Mat. 13, 151 (2014).
[2] W. F. Koehl et al., Nature 479, 84 (2011). [3] M. Widmann et al., Nature Mat. 14, 164 (2015).
Theoretical model of the dynamic spin polarization of nuclei coupled to paramagnetic point defects: application to nitrogen-vacancy center
in diamond and divacancy in SiC Viktor Ivády1,2, Krisztián Szász2,3, Abram L. Falk4,5, Paul V. Klimov4,6, David J. Christle4,6, Erik Janzén1, Igor A. Abrikosov1, David D. Awschalom4, Adam Gali2,7,*
1. Department of Physics, Chemistry, and Biology, Linköping University, Sweden 2. Institute for Solid State Physics and Optics, Wigner Research Centre for Physics, Hungarian Academy of Sciences, Budapest, Hungary 3. Institute of Physics, Loránd Eötvös University, Hungary 4. Institute for Molecular Engineering, University of Chicago, Chicago, IL 60637, USA 5. IBM T. J. Watson Research Center, 1101 Kitchawan Rd., Yorktown Heights, NY 10598, USA 6. Center for Spintronics and Quantum Computation, University of California, Santa Barbara, Santa Barbara, CA 93106, USA 7. Department of Atomic Physics, Budapest University of Technology and Economics, Budapest, Hungary * Email: [email protected] Dynamic nuclear spin polarization (DNP) mediated by paramagnetic point defects in semiconductors is a key resource for both initiating nuclear quantum memories and producing nuclear hyperpolarization. DNP is therefore an important process in the field of quantum information, sensitivity-enhanced nuclear magnetic resonance, and nuclear spin-based spintronics. Here, we describe a general model for these optical DNP processes that takes into account many microscopic characteristics of the defets. Applying this theory, we gain a deeper insight of the dynamic nuclear spin polarization process and the physics of the diamond and SiC defects. Our results are in good agreement with experimental observations and provide a detailed explanation of them. Our findings show that the defect's excited state's lifetime and electron spin coherence times are crucially important factors in the entire DNP process. Particularly, we demonstrate optically pumped dynamic nuclear polarization of 29Si nuclear spins that are strongly coupled to divacancy in 4H- and 6H-SiC. The 99 ± 1% degree of polarization at room temperature corresponds to an effective nuclear temperature of 5
K. These results lay a foundation for SiC-based quantum memories, nuclear gyroscopes, and hyperpolarized probes for magnetic resonance imaging.
Electrical detection of magnetic resonance in Si and SiC
Martin S. Brandt
Walter Schottky Institut, Technische Universität München, 85748 Garching, Germany [email protected]
In recent years, a variety of techniques has been developed allowing the detection of paramagnetic states via resonant changes of charge transport through semiconductor devices. The talk will discuss the physics of the two most prominent approaches based on single electron transistors as well as on spin-dependent recombination and will summarize the variety of conventional paramagnetic resonance techniques which could be transferred to electrical detection, mostly using Si as the material under test. The talk will then focus on the still somewhat limited amount of EDMR experiments performed on SiC, including initial data obtained in Garching.
Electrically Detected Magnetic Resonance in 4-H SiC Transistors
P.M. Lenahan,[1] C.J. Cochrane,
[2] and A.J. Lelis [3]
[1] Pennsylvania State University, University Park, PA, USA
[2] JPL, California Institute of Technology Pasadena, CA, USA [3] US Army Research Laboratory, Adelphi, MD, USA
We have utilized electrically detected magnetic resonance (EDMR) via spin dependent recombination (SDR) in 4H SiC metal oxide semiconductor field effect transistors. We have exploited the near frequency and field independence of SDR/EDMR to make EDMR observations from 16GHz, down to 85MHz, identifying several important point defects in these devices. In addition, the very wide range of frequencies utilized allow us to explore the paramagnetic centers in ways which have rarely, if ever, been utilized in semiconductor device physics studies. Perhaps the most interesting observations involve an SDR/EDMR response at half the resonance field caused by the mixing of states by magnetic dipole-dipole coupling of paramagnetic centers.[1,2,3] Since the half field response scales with the reciprocal of defect separation to the sixth power, the response provides information about the distance between the defects. [1,2,3] Because the half field response scales with the reciprocal of the resonance frequency squared, [1,2,3] the very low frequency measurements are sensitive at technologically relevant concentrations. Also of interest is the close correlation between the near zero magnetic field magnetoresistance response and the EDMR which provide a direct demonstration that the low field magnetoresistance effects are due to spin dependent recombination. [4] Another observation of interest is the likely SDR/EDMR detection of nitrogen complexes in SiC devices. [5] This is of interest because of their relevance to device operation and quantum computation. [1] C.P. Slichter, Chapter 2 of Principles of Magnetic Resonance, 3rd edition (Springer-Verlag, Berlin, Heidelberg, 1990) [2] C.J. Cochrane and P.M. Lenahan, Appl. Phys. Lett. 104,093503 (2014) [3] S.S. Eaton, K.M. Moore, B.M. Sawant, and G.R. Eaton, J. AM. Chem. Soc. 105, 6560 (1983) [4] C.J. Cochrane, P.M. Lenahan, J. Appl. Phys. 112, 123714 (2012) [5] B.R. Tuttle, T. Aichinger, P.M. Lenahan, and S.T. Pantelides, J. Appl. Phys. 114,
113712 (2013)
On the Relationship Between Near Zero-Zero Field Magnetoresistance in SiC Devices and Electrically Detected Magnetic
Resonance
P.M. Lenahan,[1] C.J. Cochrane,[2] and A.J. Lelis [3]
[1]Pennsylvania State University, University Park, PA, USA [2] JPL, California Institute of Technology Pasadena, CA, USA
[3] US Army Research Laboratory, Adelphi, MD, USA
We observe very large changes in the resistance of some SiC based devices, up to about 1% at room temperature, under certain biasing conditions. [1]We compare the zero-field response to electrically detected magnetic resonance (EDMR) amplitudes as a function of device biasing conditions and show that the EDMR and the near zero field magnetoresistance responses scale with one another and are quantitatively consistent with spin dependent recombination within the depletion region of pn- junctions. Furthermore, we show that hyperfine interactions observed in high frequency (X-band) EDMR measurements can also be detected in the near zero field magnetorsistance measurements. This result suggests that at least some of the enormous analytical power of electron paramagnetic resonance may be acquired from an extraordinarily simple measurement of resistance as a function of magnetic field. Reference: [1] C.J. Cochrane and P.M. Lenahan, J. Appl. Phys. 112, 123714 (2012)
Coherent control of single spins in silicon carbide at room temperature
Matthias Widmann1, Sang-Yun Lee1*, Torsten Rendler1, Nguyen Tien Son2, Helmut Fedder1, Seoyoung Paik1, Nan Zhao3, Sen Yang1, Ian Booker2, Andrej Denisenko1, Mohammad Jamali1, Seyed Ali Momenzadeh1, Takeshi Ohshima4, Ilja Gerhardt1,
Adam Gali5,6, Erik Janzén2, Jörg Wrachtrup11
1. Physikalisches Institut and Research Center SCOPE, University Stuttgart,
Pfaffenwaldring 57, 70569 Stuttgart, Germany 2. Department of Physics, Chemistry and Biology, Linköping University, SE-58183 Linköping, Sweden
3. Beijing Computational Science Research Center, Beijing100084, China
4. Japan Atomic Energy Agency, Takasaki, Gunma 370-1292, Japan
5. Wigner Research Centre for Physics, Hungarian Academy of Sciences, P.O. Box 49, H-1525, Budapest, Hungary
6. Department of Atomic Physics, Budapest University of Technology and Economics, Budafoki út 8, H-1111, Budapest, Hungary
Coherent spin manipulation is a key for quantum information processing (QIP) and quantum metrology (QM). Coherent spin manipulation has been performed in several systems such as quantum dots, Josephson junctions and Rydberg atoms. However all these systems need to be operated at low temperature. A promising candidate, which operates at room temperature, is the nitrogen-vacancy (NV) center in diamond. This paramagnetic defect spin (S=1) has a high spin polarization in the ground state and very stable photon emission. This combined with long spin coherence times, up to a millisecond at ambient condition, allowed rapid growth of the related research fields towards applications to QIP and QM using the NV centers. However, it is hard to perform nanometer-scale fabrication, because of the mechanical and chemical inertness of diamond. Difficulty in the fabrication of spintronic devices based on electrical spin detection also hinder integration of diamond device into modern electronic devices. By
switching the host to silicon carbide (SiC) both drawbacks can be compensated. Mature fabrication has been developed with SiC, which allows fabrication of optical cavities and various nanostructures. The better electrical properties compared to diamond even allows electrical access to spins, known as electrically detected magnetic resonance (EDMR) and tiny electronic devices like SiC nanowire field effect transistors (nwFETs). As the NV center, the optical address of single defects is also possible. In 2014 Castelletto et al reported the first single-photon source creation. Recently spin manipulation and detection from a single defect at ambient condition in SiC has been shown. Here we present our research progress on the creation of single spin qubits based on the silicon vacancy (Vsi) in SiC. We show that that it is possible to realize a low defect density via 2 MeV low dose electron irradiation in order to resolve single Vsi. To prove the single photon emission from single defects created, we present 2nd order autocorrelation measurement of the photon emission. We also show that optically detected magnetic resonance (ODMR) on these single defects is possible. We find the lower limit of a spin coherence time T2 to be close to 200 µs which is comparable with that of the NV centers in natural abundant diamond. Generally, major decoherence sources are interactions with spin bath. These are paramagnetic impurities, and nuclear spins (29Si) which interact with the central electron spin via dipolar interaction. In the tested sample, the lowered impurity concentration and the suppressed hetero nuclear spin flip-flop by an externally applied magnetic field (~300 Gauss) allow long-lived electrons spin coherence. Our theoretical expectation tells the expected T2 time in the natural abundant SiC can be close or longer than 1 ms , which is similar to that of the NV centers in the isotope pure diamond. This theoretical work is confirmed by measurement of the coherence time of ensemble defects (divacancy) in SiC at cryogenic temperature. Our report combined with the results from other research groups suggest SiC as a prospective platform for integrated spintronics, photonics and electronics in one material.
References:
1. Morton, J. J. L. & Lovett, B. W. Hybrid Solid-State Qubits: The Powerful Role of Electron Spins. Annu. Rev. Condens. Matter Phys. 2, 189–212 (2011).
2. Balasubramanian, G. et al. Nanoscale imaging magnetometry with diamond spins under ambient conditions. Nature 455, 648–651 (2008).
3. Häberle, T., Schmid-Lorch, D., Karrai, K., Reinhard, F. & Wrachtrup, J. High-Dynamic-Range Imaging of Nanoscale Magnetic Fields Using Optimal Control of a Single Qubit. Phys. Rev. Lett. 111, 170801 (2013).
4. Shnirman, A., Schön, G. & Hermon, Z. Quantum Manipulations of Small Josephson Junctions. Phys. Rev. Lett. 79, 2371–2374 (1997).
5. Treutlein, P., Hommelhoff, P., Steinmetz, T., Hänsch, T. W. & Reichel, J. Erratum: Coherence in Microchip Traps. Phys. Rev. Lett. 93, 219904 (2004).
6. Sato, T., Yokoyama, H. & Ohya, H. Electrically Detected Magnetic Resonance (EDMR) Measurements of Bulk Silicon Carbide (SiC) Crystals. Chem. Lett. 35, 1428–1429 (2006).
7. Seong, H.-K., Choi, H.-J., Lee, S.-K., Lee, J.-I. & Choi, D.-J. Optical and electrical transport properties in silicon carbide nanowires. Appl. Phys. Lett. 85, 1256 (2004).
8. Rogdakis, K. et al. 3C-silicon carbide nanowire FET: An experimental and theoretical approach. IEEE Trans. Electron Devices 55, 1970–1976 (2008).
9. Castelletto, S. et al. A silicon carbide room-temperature single-photon source. Nat Mater 13, 151–156 (2014).
10. Christle, D. J. et al. Isolated electron spins in silicon carbide with millisecond coherence times. Nat Mater 14, 160–163 (2015).
11. Widmann, M. et al. Coherent control of single spins in silicon carbide at room temperature. Nat Mater 14, 164–168 (2015).
12. Yang, L.-P. et al. Electron spin decoherence in silicon carbide nuclear spin bath. Phys. Rev. B 90, 1–6 (2014).
Recent progress in SiC-studies at the University of Stuttgart
Matthias Niethammer1, Matthias Widmann1, Sang-Yun Lee1, Ian Booker2, Takeshi Ohshima3, Adam Gali4, Nguyen Tien Son2, Erik Janzén2, Jörg Wrachtrup1
1: 3rd Institute of Physics and Research Center SCOPE, University of Stuttgart,, Pfaffenwaldring 57, 70569 Stuttgart, Germany 2: Department of Physics, Chemistry and Biology, Linköping University, SE-58183 Linköping, Sweden 3: Japan Atomic Energy Agency, Takasaki, Gunma 370-1292, Japan 4: Wigner Research Centre for Physics, Hungarian Academy of Sciences, PO Box 49, H-1525, Budapest, Hungary In our previous work, we demonstrated coherent manipulation of single spins localized in Vsi in SiC at room temperature [1]. However, several questions regarding Vsi in SiC are still unanswered. First, the foregoing measurements showed complex fine structures in optically detected magnetic resonance (ODMR) spectra from various samples at low magnetic field. Also, the ODMR yield of roughly 1 out of 10 spots was very low. In addition, we want to investigate if the excellent electrical properties of SiC allow for sophisticated electrically controlled quantum devices. The unresolved fine structure appeared in single Vsi as well as Vsi ensembles consists of 4-5 resonance peaks between 40-95MHz separated each other by 9-15MHz at zero magnetic field. A few distinct patterns of them could be observed. In this work, we show further investigation of this fine structure using isotopically purified samples. A purification to 28Si and 12C suppresses contribution from hyperfine interactions. We also present a first attempt to explain the origin of the fine structure at low magnetic field. The low ODMR yield is suspected to be caused by fast charge state conversion. For further investigation, control over the Fermi level is necessary. As one of the advantages of SiC lies in its excellent electrical condition, a delicate pin-diode device has been fabricated. By applying an electrical bias, we observe a controlled switch in
fluorescence intensity of the Vsi. This observation lays ground for understanding the charge state of Vsi and electrically controlled quantum devices. References: [1] Widmann et al., Nature Materials 14, 164–168 (2015)