記述言語：日本語   出版者・発行元：Applied Physics Express  

We demonstrate high output power UVC-LEDs from 230 to 237 nm on AlN single-crystal substrates. The UVC-LEDs show a single peak in the electroluminescence spectrum, from 20 to 300 mA. Forward voltages were typically ∼7 V at 100 mA while measured initial output powers at 237 nm, 235 nm, 233 nm and 230 nm were 2.2 mW, 1.9 mW, 1.5 mW and 1.2 mW, respectively. At 20 mA, the measured wall-plug efficiencies were 0.37%, 0.32%, 0.25% and 0.19% at the same wavelengths, respectively. These devices have demonstrated over 3600 h of lifetime operating at 20 mA.

DOI： 10.35848/1882-0786/ab65fb

Web of Science

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記述言語：日本語   出版者・発行元：Japanese Journal of Applied Physics  

We have grown a high-quality AlInSb film by metal organic vapor-phase epitaxy using tritertiarybutylaluminum (TTBAl), trimethylindium (TMIn), and tris(dimethylamino)antimony (TDMASb). In general, difficulty in the growth of AlInSb using TTBAl and TDMASb is attributed to the pre-reaction. However, we clarified that gas turbulence is dominant in AlInSb growth. To overcome this problem, we proposed a new growth sequence, in which TTBAl was irradiated at a low flow rate at the initial stage of AlInSb growth, resulting in a high crystallinity AlInSb film with a flat surface. The carbon concentration was 9 × 1016 cm-3 for Al0.18In0.82Sb which is the lowest value among those reported for other AlSb based alloys.

DOI： 10.35848/1347-4065/ab71d5

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記述言語：日本語   出版者・発行元：Japanese Journal of Applied Physics  

The irradiation intensity and temperature characteristics of each response speed sample are measured to clarify the high photosensitivity mechanism in an Al0.6Ga0.4N/Al0.5Ga0.5N metal-semiconductor-metal photodetector. A tradeoff relation could be observed between the photosensitivity and response speed when the dependence of the saturated photocurrent on the irradiation intensity was investigated by changing the irradiation intensity from 1 nW cm-2 to 45 μW cm-2. The rise time of the photocurrent after exposure to ultraviolet light was measured to determine the trap level density that was estimated to be ca. 1012 cm-2. Further, the decay time constant was obtained by investigating the dependence of the photocurrent decay time on temperature (25 °C-180 °C). By analyzing the Arrhenius plot of the decay time constant versus inverse temperature, trap level depths of 0.23 and 0.67 eV were obtained. Thus, the high photosensitivity in the Al0.6Ga0.4N/Al0.5Ga0.5N photodetector can be attributed to the carriers trapped in deep-level traps.

DOI： 10.7567/1347-4065/ab09dc

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記述言語：日本語   出版者・発行元：Applied Physics Letters  

An Al0.6Ga0.4N/Al0.5Ga0.5N metal-semiconductor-metal (MSM) deep-ultraviolet (DUV) photodetector was developed. It possesses both high photosensitivity and high rejection ratios in comparison to photomultiplier tubes (PMTs). The photodetector was designed to have a two-dimensional electron gas layer at the Al0.6Ga0.4N/Al0.5Ga0.5N hetero-interface, which plays an important role in increasing the photosensitivity. Additionally, for reducing the dark current, a V/Al/Mo/Au electrode was employed as a Schottky electrode with an appropriate barrier height. Upon irradiation with 10 μW/cm2, an extremely low dark current (10-11A) and high photocurrent (5 × 10-5A) were achieved at a bias voltage of 5 V. The photodetector was true solar-blind with a cut-off wavelength of 280 nm. A high photosensitivity of 106 A/W and a rejection ratio of 106 were realized under the irradiation of 10 nW/cm2 DUV photons. The present results revealed that the AlGaN/AlGaN MSM DUV photodetector is one of the most suitable candidates for an all solid-state photodetector with a performance superior to PMTs.

DOI： 10.1063/1.5001979

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記述言語：日本語   出版者・発行元：Applied Physics Letters  

We developed a method for fabricating high-crystal-quality AlN films by combining a randomly distributed nanosized concavo-convex sapphire substrate (NCC-SS) and a three-step growth method optimized for NCC-SS, i.e., a 3-nm-thick nucleation layer (870 °C), a 150-nm-thick high-temperature layer (1250 °C), and a 3.2-μm-thick medium-temperature layer (1110 °C). The NCC-SS is easily fabricated using a conventional metalorganic vapor phase epitaxy reactor equipped with a showerhead plate. The resultant AlN film has a crack-free and single-step surface with a root-mean-square roughness of 0.5 nm. The full-widths at half-maxima of the X-ray rocking curve were 50/250 arcsec for the (0002)/(10-12) planes, revealing that the NCC surface is critical for achieving such a high-quality film. Hexagonal-pyramid-shaped voids at the AlN/NCC-SS interface and confinement of dislocations within the 150-nm-thick high-temperature layer were confirmed. The NCC surface feature and resultant faceted voids play an important role in the growth of high-crystal-quality AlN films, likely via localized and/or disordered growth of AlN at the initial stage, contributing to the alignment of high-crystal-quality nuclei and dislocations.

DOI： 10.1063/1.5008258

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記述言語：日本語   出版者・発行元：Journal of Crystal Growth  

We have developed InAsxSb1−x-based photovoltaic infrared sensors (PVS) for room temperature operation by metalorganic vapor phase epitaxy (MOVPE). To obtain high performance, we improved the crystallinity of the InAs0.12Sb0.88 absorber layer and utilized a Ga0.33In0.67Sb electron barrier layer. An investigation of InAs0.12Sb0.88 growth conditions using a high-quality InSb buffer layer showed that we were able to obtain the smallest full-width at half-maximum (FWHM) of the X-ray diffraction omega rocking curve, 560 arcsec, for a growth temperature of 520°C for a 1 µm thick layer. Moreover, we successfully grew a Ga0.33In0.67Sb barrier layer coherently on an InAs0.12Sb0.88 absorber layer, which is the first report of GayIn1−ySb growth on Sb-rich InAsxSb1−x. An InAsxSb1−x PVS with a responsivity at wavelengths of 8–12 µm was obtained, and estimated detectivity peak at room temperature was approximately 7×107 cm Hz1/2 W−1, which is 1.3 times higher than without a Ga0.33In0.67Sb electron barrier. These results demonstrate that our InAsxSb1−x PVS is a promising device for the 8–12 µm wavelength range at room temperature.

DOI： 10.1016/j.jcrysgro.2016.12.002

Web of Science

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記述言語：日本語   出版者・発行元：Japanese Journal of Applied Physics  

High-performance AlGaN/AlGaN hetero-field-effect-transistor (HFET)-type photosensors with high photosensitivity were fabricated using p-type GaN comprising three-dimensional island crystals. The p-type GaN layers were grown on AlGaN layers at a high AlN molar fraction, and the area of p-type GaN comprising three-dimensional island crystals increased as the thickness of the p-type GaN film decreased, resulting in a reduced p-type GaN coverage ratio. The p-type GaN layers comprising three-dimensional island crystals and showing low coverage ratios were then used to fabricate HFET-type photosensors with high photosensitivity. A high light sensitivity of 1.5 × 104A/W was obtained at a source-drain voltage (VSD) of 0.5V for a photosensor with a p-type GaN thickness of 20 nm. Moreover, the dark current was suppressed to 10-10A/mm and the photosensor achieved an extremely high photocurrent to dark current density ratio.

DOI： 10.7567/JJAP.55.05FJ07

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記述言語：日本語   出版者・発行元：Japanese Journal of Applied Physics  

We report the development of high-performance AlGaN/AlN heterostructure-field-effect-transistor-type (HFET) photosensors with a p-type GaN optical gate and detection wavelengths that are restricted to 220-280 nm. These photosensors employ a two-dimensional electron gas induced at the hetero-interface between Al0.6Ga0.4N and Al0.5Ga0.5N as a highly conductive channel. In addition, a p-type GaN optical gate is employed to deplete a channel. Consequently, we obtained a high photosensitivity of over 4 × 103A/W and an externally low dark current density of approximately 5 × 10-10A/mm at a source-drain voltage of 3V. We also determined that the detection range of light wavelength in these HFET photosensors can be controlled by controlling the AlN molar fraction in the AlGaN channel layer. The results are very promising for the development of completely solar-blind high-performance photosensors with high photosensitivity.

DOI： 10.7567/JJAP.55.05FJ04

Web of Science

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記述言語：日本語   出版者・発行元：Journal of Crystal Growth  

We have investigated the electron transport properties and crystallinity of InSb films deposited on GaAs substrates. The films were grown by metalorganic vapor phase epitaxy with trimethylindium and trisdimethylaminoantimony as In and Sb sources. Using a two-step growth method and investigating growth conditions extensively, we found that the electron mobility of films either 1.0 or 1.5 μm thick strongly depended on the temperature at which the first layer (25 nm thick) was grown. The highest mobility, 61,200 cm2 V-1 s-1, was obtained at growth temperature of 260 C and the smallest full-width at half-maximum (FWHM) of the X-ray deflection rocking curve, 205 arcsec, was obtained at 320 C. These mobility and FWHM values, both of which are for a total InSb thickness of 1.5 μm, are superior to those of InSb films grown by molecular beam epitaxy. Secondary ion mass spectrometry measurements showed that below 340 C the carbon impurity concentration increased drastically with decreasing growth temperature. This carbon incorporated InSb indicated p-type behavior at low temperature by Hall measurement. These results suggest that high concentrations of carbon impurities compensated the extrinsic electrons generated from InSb/GaAs interfacial dislocations.

DOI： 10.1016/j.jcrysgro.2014.10.029

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