A5073171528- GaN-based semiconductor devices and materials
- Semiconductor materials and devices
- ZnO doping and properties
- Ga2O3 and related materials
- Metal and Thin Film Mechanics
- Semiconductor materials and interfaces
- Semiconductor Quantum Structures and Devices
- Silicon Carbide Semiconductor Technologies
- Kidney Stones and Urolithiasis Treatments
- Thin-Film Transistor Technologies
- Photocathodes and Microchannel Plates
- Ion-surface interactions and analysis
- Integrated Circuits and Semiconductor Failure Analysis
- Plasma Diagnostics and Applications
- Advancements in Semiconductor Devices and Circuit Design
- Optical Coatings and Gratings
- Acoustic Wave Resonator Technologies
- Advanced Materials Characterization Techniques
- Pediatric Urology and Nephrology Studies
- Advanced Semiconductor Detectors and Materials
- High-pressure geophysics and materials
- Thermal properties of materials
- Semiconductor Lasers and Optical Devices
- Nuclear Physics and Applications
- Solid State Laser Technologies
Osaka University
2021-2024
National Museum of Nature and Science
2024
Nagoya City University
2024
Kyoto Prefectural University
2024
Tohoku University
2024
Nagoya University
2015-2021
Kyushu University
2020
Toshiba (Japan)
2020
Graduate School USA
2019
National Institute for Materials Science
2017
Dislocations that cause a reverse leakage current in vertical p-n diodes on GaN free-standing substrate were investigated. Under high bias, dot-like spots observed using an emission microscope. Subsequent cathodoluminescence (CL) observations revealed the coincided with part of CL dark spots, indicating some types dislocation leakage. When etch pits formed dislocations by KOH etching, three sizes obtained (large, medium, and small). Among these pits, only medium spots. Additionally,...
A simple structure with high breakdown voltage and a low leakage current of vertical GaN p–n diode on free-standing substrate is demonstrated. We describe edge termination that has drift layer etched deeply vertically. device simulation revealed the electric field was more relaxed at applied uniformly in entire increasing etching depth. fabricated simulated succeeded reducing improving voltage. With this structure, stable avalanche can be observed.
Abstract The electrical characteristics of Schottky contacts on individual threading dislocations (TDs) with a screw-component in GaN substrates and the structures these TDs were investigated to assess effects such defects reverse leakage currents. Micrometer-scale platinum/GaN selectively fabricated screw- mixed-TD-related etch pits classified based pit size. Current–voltage ( I–V ) data acquired using conductive atomic force microscopy showed that very few screw generated anomalously large...
Electrical characteristics of leakage current paths in vertical-type n-GaN Schottky barrier diodes (SBDs) on free-standing GaN substrates are investigated by using photon emission microscopy (PEM). The PEM mapping shows that the initial failure SBD devices at low voltages is due to from polygonal pits epilayers. It observed these originate carbon impurity accumulation dislocations with a screw-type component microstructure analysis. For without pits, no and first appeals edge electrodes as...
A vertical p–n diode with a simple edge termination structure on GaN free-standing substrate is demonstrated. The of this device terminated simply by etching drift layer deeply and vertically. simulation revealed that the electric field at was more relaxed uniformly applied mesa deeper than depletion region. fabricated showed low leakage current avalanche capability, its breakdown characteristics could be reproduced many times. By emission microscopy observation, we found there no side wall...
Mg diffusion is a common problem in GaN devices with p–n junctions. Although this impurity reported to occur through threading dislocations (TDs), no direct evidence has yet been obtained. Therefore, we tried the observation of by atom probe tomography (APT) analysis. The n-type drift layer fabricated diode was exposed, and etch pits were formed on identify TD position. APT analysis around TDs carried out lifting specific using focused ion beam include TDs. relationship between pit shape...
Abstract We fabricated p−n diodes under different growth pressures on free-standing GaN substrates of the same quality and observed a noteworthy difference in reverse leakage current. A large current was generated by nanopipes, which were formed from screw dislocations homoepitaxial layer. There two types dislocation this study. The first type already existed substrate other newly epilayer coalescence edge mixed dislocations. An increase pressure suppressed transformation into led to...
Recent experiments suggest that Mg condensation at threading dislocations induces current leakage, leading to degradation of GaN-based power devices. To investigate this, we perform first-principles total-energy electronic-structure calculations for various and dislocation complexes. We find screw (TSDs) indeed attract impurities, the electronic levels in energy gap induced by are elevated toward conduction band as impurity approaches line, indicating Mg-TSD complex is a donor. The formation...
In semiconductor materials, doping is used mainly for controlling the electrical properties. There have been attempts to grow low‐resistivity n‐type gallium nitride (GaN) crystals by oxygen, germanium, and silicon, because a GaN substrate required reduce power losses of optical devices. However, in those efforts, crystal color turns black with increase concentration additives, even though they are shallow donors. Herein, it explained why heavily doped exhibit low transparency. From...
We investigate the influence of crystal defects on p-type GaN grown by metalorganic vapor phase epitaxy. Sets films were sapphire substrates and free-standing (F-GaN) simultaneously using various Et-Cp2Mg flow rates. Although there is a difference two orders magnitude between threading dislocation densities F-GaN substrates, no significant in hole concentration. However, are problems with surface morphology sapphire. The deterioration was caused nanopipe density. electrical properties p–n...
The propagation behavior of threading dislocations (TDs) and the effects Burgers vectors in hydride vapor phase epitaxy (HVPE) GaN bulk crystals generated on Na-flux-grown a commercially available HVPE-grown crystal were investigated. Analyses based chemical etching transmission electron microscopy (TEM) revealed close correlation between etch pit sizes vector these TDs. existence TDs with unique b = 1m + 1c was observed for first time ever using large-angle convergent-beam diffraction...
In this study, we investigated calcium oxalate (CaOx) kidney stones and showed direct evidence of the solution-mediated phase transition dihydrate (COD; metastable phase) to monohydrate (COM; stable phase). We examined crystal phases, textures, protein distributions within thin sections stones. Observation with a polarized-light microscope that outline mosaic texture, in which COM crystals are assembled pattern, roughly coincides COD's crystallographically face angles. Microfocus X-ray CT...
Abstract Calcium oxalate kidney stones, the most prevalent type of undergo a multi-step process crystal nucleation, growth, aggregation, and secondary transition. The transition has been rather overlooked, thus, effects on disease underlying mechanism remain unclear. Here, we show, by periodic micro-CT images human stones in an ex vivo incubation experiment, that growth porous aggregates calcium dihydrate (COD) crystals triggers hardening causes difficulty lithotripsy stone This was caused...
Kidney stone disease is a serious due to the severe pain it causes, high morbidity, and recurrence rate. Notably, calcium oxalate stones are most common type of kidney stone. Calcium appears in two forms stones: stable phase, monohydrate (COM), metastable dihydrate (COD). Particularly, COM with concentric structures hard difficult treat. However, factor determining growth either or COD crystals urine, which supersaturated for both phases, remains unclear. This study shows that phosphate...
In order to advance the mass production of graphene devices, it is beneficial avoid difficulty transfer process. Direct precipitation using a tungsten capping layer convenient for this purpose, and quite simple compatible with conventional semiconductor fabrication processes. study, multilayer was directly precipitated on wafer GaN-based blue LEDs form transparent electrode. The fabricated LED exhibited superior I–V characteristics emitted luminescence around probe
We acoustically measured the energy level for thermally activated conduction (TAC) in high-resistivity Fe-doped GaN using non-contacting antenna-transmission acoustic-resonance method. The acoustic attenuation takes a maximum at specific temperature, where TAC is accelerated with help of phonon energy. Debye type relaxation thus observed attenuation, and its activation (0.54$\pm$0.04 eV) was determined measurements various frequencies temperatures. This value agrees E3 GaN, indicating that...
In this study, V-shaped dislocations in a GaN epitaxial layer on free-standing substrate were observed. Our investigation further revealed that the newly generated at interface epilayer rather than propagated from substrate. consist of two straight parts. The parts separated each other m-direction and tilted toward step-flow direction layer. are continuous single having Burgers vector component 1a an intrinsic stacking fault between their
Abstract GaN crystal growth mode in the oxide vapor phase epitaxy (OVPE) method, which simultaneously provides low electrical resistance and threading dislocation density (TDD), has been investigated detail. The results clarified that these qualities can be achieved by expression of numerous inverted pyramidal pits, called three-dimensional (3D) mode. This reduced TDD from 3.8 × 10 6 cm −2 to 2.0 4 for 1 mm thick because dislocations (TDs) converged center each pit. Moreover, when surface...
In this study, vertical-type thick BGaN PIN diodes were successfully fabricated to improve the neutron capture rate of by improving epitaxial growth technique. technique, 5-μm-thick was achieved using trimethylboron as a B metal-organic source, which suppressed gas-phase reaction. The α-particle energy spectrum, pulse signal, and residual particles emitted from reaction measured performing radiation detection measurements. detected signal position in spectrum similar that 2.3 MeV...
Cell-coupled field-effect transistor (FET) biosensors have attracted considerable attention because of their high sensitivity to biomolecules. The use insect cells (Sf21) as a core sensor element is advantageous due stable adhesion sensors at room temperature. Although visualization the cell-substrate interface leads logical amplification signals, spatiotemporal processes interfaces not yet been elucidated. We quantitatively monitored dynamics Sf21 using interference reflection microscopy...
A gallium nitride (GaN) epitaxial layer with a low density of threading dislocations is successfully grown on silicon substrate by using in situ gas etching. Silicon (SiN x ) film used as mask, and ammonia intermittently supplied hydrogen ambient during the After etching, high‐density deep pits appeared surface GaN template corresponded to layer. In this novel method, before growing an additional layer, second SiN deposited after etching process, prevents nuclei from upper side‐walls pits....