Research
We have investigated wide-bandgap semiconductors (GaN, AlN, Ga2O3, and Al2O3) for photonics and electronics. Our current research interest is in the field of advanced electronic devices based on compound semiconductors and nanotechnology. We enjoy developing completely new semiconductor devices for advanced electronic and thermonic applications.
2019-2024: NEDO/Feasibility Study Program/Uncharted Territory Challenge 2050
Crystal growth
Growth of Ga2O3 and Al2O3 single crystals.
High-power and extreme-temperature devices
Fabrication of AlN diodes and transistors.
Radiation-tolerance devices
Fabrication of GaN avalanche photodiodes and pixel detectors.
Biological devices
Fabrication of photonic crystal for optogenetic and smart contact lens.
Quantum-related physics
Ballistic transport, resonant tunneling, hot electron, hopping conductance,,, etc.
These are a part of our projects. If you may have an interest in these or the other related topics, please send us an email. We can schedule a meeting where we will try to answer all your questions about our work. Thanks.
Publication
Google scholar and University of Tsukuba Repository (FREE)
Selected paper
H. Okumura, Y. Ogawara, M. Togawa, M. Miyahara, T. Isobe, K. Itabashi, J. Nishinaga, M. Imura, "Degradation of GaN diodes by radiation", JJAP 62, 064001 (2023).
H. Okumura, R. Jinno, A. Uedono, M. Imura, "Optical and electrical properties of Si-implanted Al2O3", JJAP 60, 106502 (2021).
H Okumura, S Suihkonen, J Lemettinen, A Uedono, Y Zhang, D Piedra, T Palacios, "AlN MESFETs using Si+ implantation", JJAP 57, 04FR11 (2018).
H Okumura, D Martin, M Malinverni, N Grandjean, "Backward diodes using Mg-doped GaN growth by NH3 MBE", APL 108 (7), 072102 (2016).
H Okumura, M Kita, K Sasaki, A Kuramata, M Higashiwaki, JS Speck, "β-Ga2O3 (010) growth by plasma MBE", APEX 7 (9), 095501 (2014).
Facilities
Plasma-enhanced molecular beam epitaxy
Standard model (PASCAL)
Temperature: 300-1100 K
Pressure: 5e-7 Pa (Pfeiffer, HiPace700 TC400)
Sample size: 10 mm x 10 mm
Cell: plasma oxide (ARIOS, IRFS-503), SnO2 (or SiO2), Al, Ga (Eiko, MB-3000)
Option: RHEED (Vacuum products, AHR-100), pyrometer (Japan sensor, FTK6Y), Nude ion gauge (ARIOS, BFM-2F01), QMS (ULVAC, CGM-052) , Spectrometer (Ocean optics, USB2000+)
Software: Lab view, Spectra suite
Metal-organic chemical vapor deposition
High-temperature electrical measurement system
iE model (Riko International)
Temperature: 300-1200 K (Lake Shore, Model 335)
Sample size: 20 mm x 20 mm
Magnification: 26-200x (Carton, SPZ-50D-GS-260)
Connector: TRIAX
Min. current resolution: 0.01 fA (Keysight, B2985A)
Max. voltage: 210 V (Keysight, B2902B)
Max. frequency : 1 MHz (Keysight, E4980AL/102)
Option: DC power supply (Kikusui, PMX500-0.1A), DC Voltage/Current Source/Monitor (ADCMT, 6247G), Thermometer (TESTO, 872)
Software: B2900 quick IV
High-temperature Hall-effect measurement system
VHT (Toyo corporation)
Temperature: RT-1000K (Lake Shore, Model 336)
Sample size: 10 mm x 10 mm
Resistance: 0.01~10M Ω (Lake Shore, M91)
Power supply: DC (AMETEK, DLM300-2)
Magnet: 0.567 T, permanent (MAG-WEISSS-3)
Pressure: 5e-4 Pa (Pfeiffer, DRYTEL-1025C, PKR361-NW25, TPG361) with vibration isolator (Meiritz, AVT0405S)
Water chiller: 287 K (EYELA, CA-1115B)
Software: MeasureLINK
Vacuum ultra-violet transmittance & photoluminescence measurement system
KV-202PN (Bunkoukeiki)
3D laser confocal scanning microscope
OLS5000-SAT (Olympus)
Magnification: 54x-17280x
Laser wavelength: 405 nm
Option: Differential interface prism, top-surface detection filter, film thickness measurement
Time-resolved photoluminescence measurement system
Laser: 473 nm Solid State with 75 mW CW & 150 MHz pulse (Coherent, Obis)
Sample temperature: 4-300 K (Oxford, OptistatCF)
Focal length: 320 mm (Jobin Yvon-SPEX, Triax320)
Diffraction grating: 1200 gr/mm for 250 nm, 1200 gr/mm for 750 nm, & 600 gr/mm for 1500 nm
Detector: Multialkali PMT (Hamamatsu, R2949, C9525-02), Photo diode with Amp (SIGMAKOKI, PDA-1), CCD (Ocean Photonics, FRAME-T(200-850 nm))
Photon counter: (SRS, SR400)
Pulse delay generator: (SRS, DG535)
Probe station: Metallographic microscope (Wraymer, RM-5400TL)
Option: Oscilloscope (Tektronix, TDS220), Xenon lamp (Asahi Spectra, MAX-350) with seven filters (254, 270, 290, 310, 330, 350, 370 nm), LED (Asahi Spectra, 520 nm)
Software: Matlab
Else
Water purification system (Millipore, Direct-Q UV 3)
Clean bench (Yamato, ADS101SM)
Storage cabinet (Yamato, SLK-14)
Waste container (Yamato, WF-2)
Drying oven (Yamato, DG-401)
Fine crystal cutter (ULTILE, FU-100-S)
USB camera (Goko, scorp-on direct)
Oil changer (Sato Vac, OCP-100)
Air compressor (Hitachi, LE & EDT-100)
Software
Crystal structure (HULINKS, CrystalMaker, SingleCrystal, and CrystalDiffract)
Graph (LightStone, Origin)
FDTD (Ansys Lumerical, Ansys)
Device design (Autodesk, AutoCAD)
Collabolations
Industry
Academic
