A5074195503- Ga2O3 and related materials
- GaN-based semiconductor devices and materials
- ZnO doping and properties
- Semiconductor materials and devices
- Semiconductor Quantum Structures and Devices
- Advanced Photocatalysis Techniques
- Gas Sensing Nanomaterials and Sensors
- Acoustic Wave Resonator Technologies
- Electronic and Structural Properties of Oxides
- Magnesium Oxide Properties and Applications
- Luminescence Properties of Advanced Materials
- Photocathodes and Microchannel Plates
- Thin-Film Transistor Technologies
- Copper-based nanomaterials and applications
- Optical Coatings and Gratings
- X-ray Diffraction in Crystallography
- Aluminum Alloys Composites Properties
- Advanced Welding Techniques Analysis
- Transition Metal Oxide Nanomaterials
- Atomic and Molecular Physics
- Perovskite Materials and Applications
- Crystal Structures and Properties
- Metal and Thin Film Mechanics
- Thermography and Photoacoustic Techniques
- Chalcogenide Semiconductor Thin Films
Kogakuin University
2016-2025
Nihon University
2025
National Institute of Information and Communications Technology
2013-2021
Kyoto University
2021
Tokyo Metropolitan Industrial Technology Research Institute
2021
Kyoto Katsura Hospital
2021
Advanced Engineering (Czechia)
2021
Kokugakuin University
2019-2020
National Institute for Materials Science
2018
Tohoku University
2008-2017
A near-band-edge bluish electroluminescence (EL) band centered at around 440 nm was observed from ZnO p-i-n homojunction diodes through a semi-transparent electrode deposited on the p-type top layer. The EL peak energy coincided with photoluminescence of an equivalent layer, indicating that electron injection n-type layer to dominates current, giving rise radiative recombination in imbalance charge is considered originate lower majority carrier concentration which one or two orders magnitude...
Temperature-dependent cathodoluminescence spectra were measured from (001) unintentionally doped, (100) Si-doped, and (010) Mg-doped β-Ga2O3 substrates prepared by either the floating zone growth or edge-defined film-fed methods. Although is expected to be an indirect bandgap material, direct Γ-Γ transitions found dominant in optical transmittance spectra. The exhibited no near-band-edge emission instead ultraviolet luminescence, blue luminescence (BL), green bands. Since BL intensity...
The polarized transmittance and reflectance spectra of β-Ga2O3 crystals are investigated, the data interpreted in terms monoclinic crystal band structure. energies absorption edge can be divided into six ranges, these ranges assigned to transitions from valence bands conduction minimum according selection rules. indirect bandgap-energy 4.43 eV is smaller than direct 4.48 at RT; energy difference 0.05 nearly matches theoretically calculated values 0.03–0.04 eV.
We have grown nitrogen-doped MgxZn1−xO:N films on Zn-polar ZnO single crystal substrates by molecular beam epitaxy. As N-sources, we employed NO-plasma or NH3 gas itself. x increased, optimum growth temperature window for smooth film morphology shifted to higher temperatures, while maintaining high N-concentration (∼1×1019 cm−3). The heterosructures of (0.1≤x≤0.4)/ZnO were fabricated into light emitting diodes 500-μm-diameter. observed ultraviolet near-band-edge emission (λ∼382 nm) with an...
Temperature-dependent cathodoluminescence spectra of (2¯01) Si-doped β-Ga2O3 single crystals and (010) N-doped epitaxial films were comprehensively shown to investigate their electronic structure defect states. The decrease in the self-trapped exciton (STE) emission at low temperatures heavily implied Debye-Hückel screening STEs with critical charge density larger than 2 × 1018 cm−3. analysis based on rate equation model suggested a significant influence donor-acceptor-pair recombination...
Crystalline oxides spanning very broad 5.4- to 8.6-eV bandgaps are successfully grown on sapphire by MBE.
Temperature-dependent exciton resonance energies Eexciton in β-Ga2O3 single crystals are studied by using polarized reflectance measurement. The values exhibit large energy changes the range of 179–268 meV from 5 to 300 K. IR-active Au and Bu optical phonon modes selectively observed IR spectroscopic ellipsometry spectra reflecting polarization selection rules. longitudinal (LO) can be divided into three ranges: ℏωLO = 35–48, 70–73, 88–99 meV. broadening parameters, which obtained...
Room-temperature nonradiative lifetime (τnr) of the near-band-edge excitonic photoluminescence (PL) peak in {0001} polar, (112¯0), (11¯00), and (001) nonpolar GaN was shown to increase with decrease density or size Ga vacancies (VGa) gross point defects including complexes, leading PL intensity. As edge threading dislocation decreased, VGa tended τnr increase. However, there existed remarkable exceptions. The results indicate that recombination process is governed not by single defects, but...
The internal quantum efficiency (ηint) of the near-band-edge (NBE) excitonic photoluminescence (PL) in ZnO epilayers was significantly improved by eliminating point defects, as well use high-temperature-annealed self-buffer layer (HITAB) on a ScAlMgO4 substrate epitaxial templates. Negatively charged Zn vacancy (VZn) concentration greatly reduced high-temperature growth, and slower postgrowth cooling (annealing) under minimum oxygen pressure further gross positively negatively neutral...
Vacancy-type defects in AlN grown by metal-organic vapor phase epitaxy (MOVPE) and lateral epitaxial overgrowth (LEO) using halide were probed a monoenergetic positron beam. Doppler broadening spectra of the annihilation radiation measured compared to calculated projector augmented-wave method. For MOVPE-AlN, concentration vacancy-type was high near interface between GaN buffer layer, defect-rich region expanded from toward surface when NH3 flow rate increased. sample on however,...
Heat input is one of the key parameters governing quality and service properties friction stir welds. By using a calorimetric technique, heat inputs generated during welding aluminium alloys, 1100 5083, were measured over wide range parameters. An empirical equation to estimate was established based on multiple regression analysis results. The effect final grain size zone also investigated by electron backscatter diffraction method. quantitative relationships between variables, inputs, sizes...
Radiative and nonradiative processes in nearly strain-free AlxGa1−xN alloys were studied by means of steady-state time-resolved (TR) photoluminescence (PL) spectroscopy, the results connected with that positron annihilation measurement. The optical reflectance PL measurements gave bowing parameter b approximately −0.82 eV. Values full width at half maximum (FWHM) near-band-edge peak agreed those predicted classical alloy broadening model. However, Stokes-type shifts (SS) as large 100–250 meV...
Radiative and nonradiative recombination dynamics in strained cubic (c-) In0.1Ga0.9N/c-GaN multiple quantum wells were studied using temperature-dependent time-resolved photoluminescence (TRPL) spectroscopy. In contrast to hexagonal InGaN wells, low-excitation peak energy increased moderately with decreasing well thickness L the PL lifetime did not strongly depend on L. The results clearly indicated that piezoelectric field was acting transition process. TRPL signal fitted as a stretched...
Prospective equivalent internal quantum efficiency (ηint) of approximately 34% at 300K was demonstrated for the blue emission peak nonpolar m-plane (11¯00) InxGa1−xN∕GaN multiple well light emitting diodes (LEDs) fabricated on freestanding GaN substrates. Although ηint value is yet lower than that conventional c-plane LEDs (>70%), results encourage one to realize high performance green, amber, and red by reducing concentration nonradiative defects, according absence quantum-confined...
Anisotropic optical properties are investigated on β-Ga2O3 films and a single crystal by spectroscopic ellipsometry measurements. The grown (0001) α-Al2O3 contain threefold in-plane rotational domains, the refractive index absorption coefficient α obtained assuming an isotropic material found to be smaller than those in crystal. By measuring off-normal transmission spectra of (010) substrate, anisotropy biaxial as well gradual increase recognized origins scattering optically determined...
We report the use of suboxide molecular-beam epitaxy (S-MBE) to grow α-(AlxGa1−x)2O3 films on (110) sapphire substrates over 0 < x 0.95 range aluminum content. In S-MBE, 99.98% gallium-containing molecular beam arrives at substrate in a preoxidized form as gallium (Ga2O). This bypasses rate-limiting step conventional MBE for growth oxide (Ga2O3) from and allows us fully epitaxial rates exceeding 1 µm/h relatively low temperature (Tsub = 605 ± 15 °C). The ability nominally full...
A promising approach to obtain epitaxial films of oxide semiconductors was demonstrated, namely helicon-wave-excited-plasma sputtering epitaxy. Due the surface-damage-free nature, completely a-axis-locked c(0001)-orientation ZnO epilayers were successfully grown on sapphire (0001) substrates having ultrasmooth surfaces with atomic steps. The epilayer exhibited a dominant near-band-edge photoluminescence (PL) peak at 300 K. Since PL considered be due recombination excitons bound an impurity...
Static and dynamic responses of excitons in state-of-the-art bulk epitaxial ZnO are reviewed to support the possible realization polariton lasers, which coherent monochromatic light sources due Bose condensation exciton–polaritons semiconductor microcavities (MCs). To grasp current problems pave way for obtaining epilayers improved quality, following four principal subjects treated: (i) polarized optical reflectance (OR), photoreflectance (PR) photoluminescence (PL) spectra were recorded at...
Exciton resonance energies in an AlN epilayer on (0001) sapphire substrate grown by low-pressure metalorganic vapor phase epitaxy were determined as a function of temperature means optical reflectance (OR) and cathodoluminescence measurements. The OR spectra exhibited distinct anomalies at the photon just above multiple internal reflection fringes, spectral line shape was fitted considering A (Γ7vu→Γ7c) BC (Γ9v,Γ7vl→Γ7c) exciton transitions. fitting gave values them 0 K to be 6.211 6.266 eV,...
Exciton fine structures were observed in partially polarized optical reflectance and cathodoluminescence (CL) spectra of AlN epilayers grown by low-pressure metalorganic vapor phase epitaxy on (0001) Al2O3 substrates. A few free four bound exciton lines clearly resolved the low-temperature CL lowest threading dislocation density (∼1×108 cm−2) film. From energy difference between ground-state first excited states, hydrogenic A-exciton binding present compressively strained (Δa/a≈−1.68%) was...