epitaxial growth and characterization of semiconducting ... · scopus: ga2o3 in title, abstract,...
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Epitaxial growth and characterization of semiconducting materials and nanostructures
TeamMatteo Bosi
Claudio FerrariPaola FrigeriEnos GombiaLuca Seravalli
Giovanna Trevisi
ActivitiesSynthesis and study of semiconducting materials and nanostructuresModelling of electronic properties of quantum confined systems
Developing new tools and methods for structural and electrical characterization
Scientific areas of interest:Structures tailored to sensing: nanowires, quantum dot, microtubes, MEMSMaterial for photonicsMaterial for power devices
SkillsEpitaxial growth (MOVPE, ALD, MBE)
Materials: Ge, Ga2O3, SiC, III‐VCharacterization of semiconductors and nanostructures:
Morphological (SEM, AFM)Structural (XRD)Optical (PL, transmission, reflectance)Electrical
Micro/nano fabrication by focused ion beam PhotolitographyDesign / modeling of quantum, nano and photonic structures
UdR “Growin”
UdR “Growin”
Overview of the main facilities:
2x MOVPEMBEXRD systems (high resolution, 2D detector)Clean room with laminar hood for chemical preparationPhotoluminescence, transmittance, reflectanceElectrical characterizationTiberCAD software for nanostructures modelling
UdR “Growin”
Main facilities:MOVPE (1)
Designed for 3C‐SiC / Si epitaxyNow used to grow Ge and Si nanowires
max T 1500 °Cmin P 100 mbarH2, Ar atmosphereSubstrate area 2x4 cm2
Sources:2 main gas lines ‐ SiH4, C3H82x metal organic lines ‐ Ge, Ga, Al, As, P, Zn, Indisposable cylinders (12L, 1bar) ‐ N2, C2H4, C2H6
UdR “Growin”
Main facilities:MOVPE / ALD (2)
Designed for oxides / ALD is possibleNow used to grow Ga2O3
max T 600 °Cmin P 100 mbarH2, N2 atmospheresubstrate area: 2’’
Sources:1 main gas line ‐ SiH43x metal organic lines – Ga, H2O, Ti, Al
UdR “Growin”
Main facilities:MOVPE / ALD (2)
In the past: Al2O3 and TiO2 layers by ALD
… but ALD had some technical problemsHardware upgrade is necessary for development
Conformal
Conformal deposition of high aspect‐ratio structuresPrecise control of thickness / n° of layers
UdR “Growin”
Main facilities:MBE Equipment
Group III (Ga, In, Al) effusion cellsAs valved cracker cellSi, Be doping sourcesIn‐situ diagnostic: RHEEDClean room (class 100 and class 10000)
Present situationGrowth activity suffers from technical problemsand lack of adequate fundings
The MBE growth techniques allows for the depositionof thin layers of semiconducting materials with highcrystal quality, reduced incorporation of undesiredimpurities, controlled doping and compositionprofiles along the growth direction, atomic‐scalesmoothness of the interfaces.
UdR “Growin”
Main facilities:Optical characterization
Photoluminescence Spectroscopy, Reflectance, Transmittance532 nm laser10 ‐ 300 K Fourier transform spectrometerLiquid N2 Cooled Ge Detector
Electrical characterizationElectrical measurements (10‐330 K)Preparation of Ohmic and Schottky contacts by thermal evaporation and annealing I‐V, C‐V, Deep Levels Transient Spectroscopy, Admittance Spectroscopy
UdR “Growin”
Main facilities:Tiber CAD – modelling software
Software tool for numerical simulation of electronic and optoelectronic devicesModelling and design of nanostructured devices
e.g.: III/V LEDs, nanowire FETs, Dye Solar CellsAtomistic and continuous finite element method models availableExtensive material database: zincblend and wurtzite, ternary and quaternary alloys1D/2D/3D modeling and meshing, cylindrical symmetryAvailable modules:
thermalelasticitydrift‐diffusionenvelope function approximation
UdR “Growin”
Main facilities:Structural characterization by X‐Ray Diffraction
High resolution XRD Panalytical Xpert‐Pro with Goebel mirror and crystal analalyser: reciprocal lattice maps in high or medium angular resolution and x‐ray polar maps
XRD with Goebel mirror for powder monochromatic diffraction and thin film characterizationDouble crystal x‐ray topography camera for large crystal charcateriztion
-3.3 -3.2 -3.1 -3 -2.9
4.35
4.4
4.45
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4.6
4.65
4.7
kx (1/Å)
ky (1
/Å)
Si1455m3
0
0.5
1
1.5
2
2.5
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4.5
Si 422 peak
Ge 422 peak
Strained422 SiGeLayer peak
n̂
NATO Science for Peace program – grant SPS G5423 (2018 – 2020)“Portable sensors for unmanned explosive detection” (P.I. : Claudio Ferrari)
Participants: IMEMChemistry dept. UniPRAzerbaijian National Academy of Sciences
Funding
Partner Countries 140.000
NATO countries (Azerbaijian) 200.000
Total (3y) 340.000
Aims Preparation of explosive sensors based on functionalized semiconductor nanowires or carbon nanotubes Very limited mass, power consumption and dimension. Tailored for installation in an unmanned drone
NATO Science for Peace – nanostructures for explosive detection
Semiconducting nanowiresGe as a “new” semiconducting material for (nano)devices:
direct bandgap=0.8 eVindirect bandgap=0.66 eVhigher carrier mobilitylarger Bohr radius: stronger confinementlower deposition temperature has been proposed for next generation high transportchannel devices and nanodevices
Ge NW growth is now well assessed in IMEMAu nanoparticles as catalyst“novel” metal‐organic Ge precursor: Isobutyl GermaneWide range of growth conditions explored
Si NW growth is planned
Ge NW processing:sonication to detach NW from the substratesingle‐NW electrical characterizationchemical functionalization in progress
NATO Science for Peace – nanostructures for explosive detection
NATO Science for Peace – nanostructures for explosive detection
Single Ge NW, about 15 m long
Pt contact (FIB)
Metal contact pads
SiO2/Si substrate
resistivity ≈ 0.05‐0.07 Ωcm
Electrical characterization of single Ge NW
Uncapped QDs for molecular sensing: PL study and theoretical modeling
Sensing devices based on nanostructuresSensing of polar moleculesEfficiency + reliability + compactness
Nanostructures: uncapped InAs/GaAs QDsPL emission depends on the external environment (humid vs dry)
Uncapped QDs for molecular sensing: PL study and theoretical modeling
Intensity and emission energy of PL spectra change upon the exposure to humid environmentModeling: the cause are oxidation of uncapped QDs and passivation of surface states
Fabrication of 3D architectures by strain‐induced self‐rolling MBE bilayers
Sensing devices based on nanostructuresMicrofluidics channels for sensingNovel microtube‐based photonic integrated components
Highly ordered array of 3D‐objectsPrecise positioning (top‐down approach)Perfect single‐crystal qualityBilayer overgrowth with functional layers
Fabrication of 3D architectures by strain‐induced self‐rolling MBE bilayers
tube‐wall thickness control at the nm scale
lateral view
Sensing devices based on nanostructuresMicrofluidics channels for sensingNovel microtube‐based photonic integrated components
Novel oxide semiconductors
Gallium Oxide ‐ Ga2O3 researchA new material for very high power devices and deep‐UV detectors
IMEMPhysics dept. UniPR(+ national and international network of collaborators)
Ga2O3 key properties:bandgap: 4.7 – 4.9 eVbreakdown field: 8 MV cm‐1
Applications: Potentialities for device performances beyond GaN and SiC for
very high power applications Solar blind UV‐detectors
Novel oxide semiconductors
Aims Basic material science to realize, characterize and understand a “new” compound Build test devices (electrical, optical sensors)
Critical issuesGa2O3 has several polymorphs:
most interesting: ‐Ga2O3 (stable, grown at 800‐900 °C)our phase, ‐Ga2O3, is metastable but still technologically relevant
We should upgrade the growth systemRealize test devicesStill no fundings despite several proposal submitted
Interest in Ga2O3 is increasing rapidly…
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Scopus: Ga2O3 in title, abstract, keywords
Novel oxide semiconductors
pubblicazione citazioniHetero‐epitaxy of ε‐Ga2O3 layers by MOCVD and ALD giu‐16 35Crystal structure and ferroelectric properties of ϵ‐Ga2O3 films grown on (0001)‐sapphire nov‐16 29The real structure of ε‐Ga2O3 and its relation to κ‐phase feb‐17 20ε‐Ga2O3 epilayers as a material for solar‐blind UV photodetectors feb‐18 9Thermal stability of ε‐Ga2O3 polymorph nov‐17 7
Dedicated conference, workshop, focused sessions
Main drivers: Japan, USA (US‐Army), Germany
Solar‐blind UV Photodetectors
4.41 Ev3.92 Ev 6.18 Ev
Detection of weak UV radiation on vis‐IR backgrounds:• There is no terrestrial background at less than 280 nm (UVC)• Heat sources (flames, jet engines, or missile plumes) emit UVC
Easy detection of emitters at wavelengths less than 280 nm: “solar blind” UV detector
Applications: detect missile plume, airplane engines (security) flame monitoring in boiler control and fire‐safety equipment UV exposure control in photolithographic and binder curing processes imaging of UV objects in astronomy UV sensing elements in advanced medical and biological instruments
‐Ga2O3 is suitable for detection of deep‐UV radiation • Very basic test device already proved
Novel oxide semiconductors
Bandgap of ‐Ga2O3 ~ 4.6 eV (270 nm)
Silicon Carbide (3C‐SiC)for: MEMS (Micro Electro Mechanical Systems)
Defects in 3C‐SiC as single photon sourcePower devices
VPE growth in hot‐wall reactor (up to 1400 °C) State of the art 3C‐SiC deposited on silicon substrates (2x4 cm2)n‐type dopingnational and international network of collaborators
Activity is now in standby: the reactor is used for NATO project nanowiresAims
A material useful for micro mechanical sensors A new platform for single photon emission and quantum optical structures
No more fundings. In the past (2015‐2018): about 60K € from a company to develop a 3C‐SiC epitaxial process for power devices
3C‐SiC
3C‐SiC
Optical microscope
Suspended 3C‐SiC/Si MEMS structures to be used as high‐sensitivity strain sensors (e.g. engines)high T applications (up to 500 °C)ultra high‐resolution enhanced sensitivity with respect to standard Si design
IMM‐Bologna
3C‐SiC
A new platform for single photon emission and quantum optical structures
Collaboration with RMIT Melbourne, Australia
Single photon source (SPS):emits one photon at a timeat a time decided by the userwith adjustable repetitionhighly polarisedindistinguishable photons
Some defects in SiC can act as SPS, created by:implantation+annealoxidation
3C‐SiC
SPS formation by 3C‐SiC oxidation and anneal
Photon antibounching measurement
3C‐SiC
Fabrication of optical disk resonator suspendedIMEM 3C‐SiC
Si substrate
Integration of SPSinto a disk resonator
Confocal microscope used to probe signel defect and define a disk mask aligned accordingly
Single/entangled photon at telecom wavelengths by metamorphic InAs/InGaAs QDs
Metamorphic InAs/InGaAs QDs
Metamorphic InAs QDs by MBE
Thermally stimulated current:defect density in metamorphic QDs is comparable to standard In(Ga)As QDs
Photocurrent: a good photoresponsitivity in the C‐, S‐ and E‐bands is preserved in metamorphic QDs
Metamorphic InAs/InGaAs QDs
Golovynskyi S, Datsenko O I, Seravalli L, Trevisi G, Frigeri P, Babichuk I S, Golovynska I and Qu J 2018 Nanoscale Research Letters 13 103
Golovynskyi S, Datsenko O I, Seravalli L, Trevisi G, Frigeri P, Babichuk I S, Golovynska I and Qu J 2019 Semiconductor Science and Technology (in press)
Single/entangled photon at telecom wavelengths by metamorphic InAs/InGaAs QDs
Scientific areas of interest:Strucutres tailored to sensing (nanowires, quantum dot, microtubes, MEMS)Power devicesPhotonics
Skills:Epitaxial growth (MOVPE, ALD, MBE)
Materials: Ge, Ga2O3, SiC, III‐VCharacterization of semiconductors and nanostructures:
Morphological (SEM, AFM)Structural (XRD)Optical (PL, transmission, reflectance)Electrical
Focused ion beam micro/nano fabricationphotolitographyDesign / modeling of quantum structures and photonics structures
Main facilities:2x MOVPEMBE for semiconductor epitaxyXRD systems (alta risoluzione, detector 2D)Photoluminescence, transmittance, reflectanceClean room for chemical preparation with laminar hoodElectrical characterizationTiberCAD software modelling
UdR “Growin” – in conclusione
UdR “Growin”
fine
3C‐SiC
NATO Science for Peace – nanostructures for explosive detection
The problem / main motivations Enhanced needs for security Detection of explosives (Improvised Explosive Devices) Safety of infrastructures (airports, railway stations, roads, buildings, …)
Current solutions Different technologies to detect threats (e.g. explosives)
mass spectroscopy gas chromatography (GS) Laser Induced Breakdown Spectroscopy (LIBS) infrared absorption (IR) Raman spectroscopy (RS) ….
Future needs Higher sensitivity Broad sensing Portable sensors with limited weight and power consumption No human intervention: unmanned exploration of dangerous sites
Overview &Milestones Synthesis of materials tailored for explosive detection
semiconducting nanowires: germanium, siliconcarbon nanotubes
Chemical functionalizationelectron‐rich amino‐silanecharge‐transfer donor‐acceptor interactions sharp changes in the conductance of the electrical‐sensing nanoelements
SensingTNT, Dinitrobenzene, Nitroamine , Nitrobenzene, 2‐Nitrotoluene, etc
Devicefunctionalized nanowires in FET configurationcurrent change in functionalized carbon nanotubes
2018
2020
NATO Science for Peace – nanostructures for explosive detection
Overview &Milestones Synthesis of materials tailored for explosive detection
semiconducting nanowires: germanium, siliconcarbon nanotubes
Chemical functionalizationelectron‐rich amino‐silanecharge‐transfer donor‐acceptor interactions sharp changes in the conductance of the electrical‐sensing nanoelements
SensingTNT, Dinitrobenzene, Nitroamine , Nitrobenzene, 2‐Nitrotoluene, etc
Devicefunctionalized nanowires in FET configurationcurrent change in functionalized carbon nanotubes
2018
2020
NATO Science for Peace – nanostructures for explosive detection