A5056333861- Chalcogenide Semiconductor Thin Films
- Semiconductor Quantum Structures and Devices
- Thermography and Photoacoustic Techniques
- GaN-based semiconductor devices and materials
- Quantum Dots Synthesis And Properties
- Silicon and Solar Cell Technologies
- Advanced Semiconductor Detectors and Materials
- Nanowire Synthesis and Applications
- Semiconductor materials and devices
- solar cell performance optimization
- Semiconductor materials and interfaces
- Photoacoustic and Ultrasonic Imaging
- Thin-Film Transistor Technologies
- ZnO doping and properties
- Diamond and Carbon-based Materials Research
- Thermal properties of materials
- Machine Learning in Materials Science
- Ga2O3 and related materials
- Advancements in Semiconductor Devices and Circuit Design
- Force Microscopy Techniques and Applications
- Gas Sensing Nanomaterials and Sensors
- Metal and Thin Film Mechanics
- Advanced Thermoelectric Materials and Devices
- Ion-surface interactions and analysis
- Integrated Circuits and Semiconductor Failure Analysis
University of Miyazaki
2014-2024
Japan Society for the Promotion of Science
2022
The University of Tokyo
2020
Kyushu University
2010
Fukuoka Institute of Technology
2003-2006
Abstract To reduce fluctuations in the performance of lattice-mismatched solar cells within a wafer, it is necessary to characterize and quantify effect misfit dislocations, caused by strain relaxation, on cell. this end, relationship between preferential glide planes (GPs) carrier generation-recombination process InGaAs with low (LowV) high (HighV) open-circuit voltages has been investigated study. The GPs β dislocations HighV were uniformly controlled wafer plane. However, LowV contained...
The optical properties of ZnO nanorods and nanowires grown by our newly developed nanoparticle-assisted pulsed-laser deposition (NAPLD) technique were studied photoluminescence (PL) spectroscopy. This NAPLD technique, which does not require a catalyst for crystal growth, is expected to synthesize high-quality nanostructured crystals. green luminescence (GL) band ultraviolet (UVL) observed at low temperature investigated these UVL consists several sharp emission lines due free excitons,...
Time evolution of $\mathrm{EL}2$ thermal recovery has been investigated in detail by a piezoelectric photothermal method. Results showed simple saturating behavior for $T>120\mathrm{K}$ and sigmoid-function-like $T<120\mathrm{K},$ which were both quantitatively analyzed with an autocatalytic-reaction rate equation. The latter mode indicates correlation between defects, promotion charge transfers from recovered to unrecovered defects can be suggested. A three-center-complex model...
The spectral and the time dependent piezoelectric photoacoustic (PPA) measurements under continuous light illumination were carried out at 85 K to investigate nonradiative recombination processes involving EL2 defect levels in carbon concentration controlled not intentionally doped semi-insulating (SI) GaAs. decrease of PPA signal due photoquenching effect is observed for a short period photon energy region from 1.0 1.3 eV. Since almost all acceptors are compensated by deep donor SI GaAs,...
Starting on June 2011, NGCPV has been the first coordinated project between European Commission and Japanese NEDO in order to advance science technology of concentrator photovoltaics (CPV). Research covered all relevant areas CPV, from solar cells complete systems, including multijunction cells, novel cell concepts utilizing nanostructures, advanced optics modules, thermal management, reliability modeling at stages CPV chain, rating round robin schemes development characterization tools for...
To investigate the effect of miniband formation on optical absorption spectrum, we adopted two non-destructive methodologies piezoelectric photothermal (PPT) and photoreflectance (PR) spectroscopies for strain-balanced InGaAs/GaAsP multiple quantum-well (MQW) superlattice (SL) structures inserted GaAs p-i-n solar cells. Because barrier widths SL sample were very thin, formations caused by coupling wave functions between adjacent wells expected. From PR measurements, a critical energy...
The carrier mobility of solar cell materials is a critical physical parameter that determines the series resistance. Furthermore, resistance an essential factor affecting conversion efficiency concentrator cells under high sunlight illumination. However, there has been slight discussion regarding relationship between these factors. In previous study, it was reported concentrated illumination decreased mobility; however, scattering mechanism not yet clarified. Moreover, carrier–carrier...
Piezoelectric photoacoustic (PA) measurements of molecular-beam-epitaxial (MBE) -grown GaAs layers were carried out in the temperature range from 90 to 290 K. A broad D band with a maximum near 1.3 eV and sharp Q peak at 1.485 have been observed 90-K spectra. They vanish presence secondary light illumination. By comparing optical-absorption spectra, it is considered that due electron transitions involving EL2 deep defect levels substrate. The PA signal be enhanced by electric field interface...
The temperature variation of the piezoelectric photo-thermal (PPT) signal intensity semi-insulating (SI) GaAs from 20 to 150 K was measured. Four peaks at 50, 70, 110, and 125 were observed in PPT signal. From theoretical analysis based on rate equations electrons conduction band deep levels, we concluded that four due nonradiative electron transitions through EL6, EL7, EL15, an unspecified level, respectively. Deep levels with extremely low concentration (1012–1015 cm−3) clearly identified...
CuInSe 2 (CIS) films with Cu/In ratios of γ=0.82–1.79 have been grown on a GaAs (001) substrate by molecular beam epitaxy. Piezoelectric photoacoustic (PPA) measurements were carried out from liquid helium to room temperature investigate nonradiative carrier recombination processes in comparison photoluminescence (PL) which directly detected radiative processes. Three PPA signal peaks corresponded band gap energies the CIS (AB and C bands) substrate, clearly obtained between temperatures. A...
Piezoelectric photothermal measurements of an AlxGa1−xAs (x=0.22, 0.28, and 0.5) epitaxial layer grown on a GaAs substrate were carried out in the temperature range 297 to 80 K. In addition band gap signal substrate, direct transition gaps AlGaAs clearly observed higher photon energy region. It was experimentally confirmed that coefficient alloy decreases with increasing Al mole fraction. By conducting quenching light illumination at K we concluded photoexcited electrons drifted under...
Three non-destructive methodologies, namely, surface photovoltage (SPV), photoluminescence, and piezoelectric photothermal (PPT) spectroscopies, were adopted to detect the thermal carrier escape from quantum well (QW) radiative non-radiative recombinations, respectively, in strain-balanced InGaAs/GaAsP multiple-quantum-well (MQW)-inserted GaAs p-i-n solar cell structure samples. Although optical absorbance signal intensity was proportional number of QW stack, intensities SPV PPT methods...
Piezoelectric photoacoustic (PA) measurements on liquid-encapsulated-Czochralski-grown n-GaAs were carried out at room temperature. A continuous broad band below 1.35 eV and a peak 1.383 observed in the PA amplitude spectra. By comparing with optical-absorption spectra, it is concluded that due to electron transition involving EL2 deep-lying defect levels. For eV, origin considered be dislocation related. The possibility this an apparent one expected from proposed models for signal generation denied.
Piezoelectric photothermal spectroscopy (PPTS) measurements were carried out on InxGa1-xN (x=0.01–0.32) thin films grown by radio-frequency molecular beam epitaxy. We found that the band energy shifts to lower side of spectrum (red shift) with an increase in indium composition from 0.01 0.32. For samples a composition, we able observe exciton contribution, and binding was estimated be 27 meV (x=0.01). Since conventional photoreflectance (PR) unable signals for higher content (x=0.13, 0.2,...
The band gap and exciton binding energies of dilute nitride ${\mathrm{Ga}}_{1\ensuremath{-}y}{\mathrm{In}}_{y}{\mathrm{N}}_{0.012}{\mathrm{As}}_{0.988}$ films with the thickness $100\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ were determined as a function indium composition for investigating effect strain on electronic structure. high sensitive piezoelectric photothermal (PPT) methodology was used measuring optical absorption spectra. fitting analysis carried out to eliminate influence determine...
Abstract The carrier collection efficiencies of InGaAs/GaAsP superlattice (SL) photovoltaic structures were optimized by choosing adequate manufacturing parameters, such as the composition and thickness quantum wells (QWs) barrier layers. However, no insights have been observed from viewpoint nonradiative transition photoexcited carriers. In this study, piezoelectric photothermal (PPT) photoluminescence (PL) measurements performed a function temperature 100 to 340 K. Using transducer, PPT...
Effect of secondary-light illuminations $h\ensuremath{\nu}=0.9$ and 1.45 eV on photoquenched photoenhanced states in semi-insulating GaAs are investigated using piezoelectric photoacoustic (PPA) measurements at 80 K. It is found that the 0.9 cause an optical recovery PPA signal from $\mathrm{EL}{2}^{*}$ to ${\mathrm{EL}2}^{0}.$ We observed appearance a broad band 0.8--1.0 spectrum after illumination eV. The most important finding spectra both same whole photon-energy region. conclude...
Room-temperature piezoelectric photothermal spectroscopy (PPTS) and surface photo-voltage (SPVS) were carried out on two types of Si p–n junction sample to investigate carrier recombination processes at the interface. It was found that SPVS peak positions each spectrum depend direction illumination: a 1.18 eV for substrate-side illumination 1.25 epitaxial-layer-side illumination. We concluded position corresponds specific photon energy which optical penetration length is equal distance from...
Dilute nitrides are novel III–V semiconductors that have been developed for photonic and electronic devices. Although they investigated, some of their characteristics not established yet. In this study, the static dielectric constant dilute was experimentally estimated from exciton binding energy. The results imply nitrogen incorporation in decreases both bandgap. This behavior is opposite to conventional semiconductors.