Yasuyuki Miyamoto
Tokyo Institute of Technology
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Featured researches published by Yasuyuki Miyamoto.
IEEE Journal of Quantum Electronics | 1986
Masahiro Asada; Yasuyuki Miyamoto; Yasuharu Suematsu
Gain and threshold current density are analyzed for quantum-box lasers where electrons are confined in quantum well three-dimensionally, based on the density-matrix theory of semiconductor lasers with relaxation broadening. The electronic dipole moment and its polarization dependence are first analyzed, and it is shown that the gain becomes maximum when the electric field of light is parallel to the longest side of the quantum box. Calculated gain is about 10 times that of bulk crystal for 100 A × 100 A × 100 A GaAs/Ga 0.8 Al 0.2 As quantum box, and 15 times for Ga 0.47 In 0.53 As/InP quantum box with the same size, respectively. The threshold current density are 45 A/cm2and 62 A/cm2for GRINSCH GaAs/(Ga 0.8 Al 0.2 As-Ga 0.4 Al 0.6 As) and Ga 0.47 In 0.53 As/(Ga 0.28 In 0.72 As 0.6 P 0.4 -InP), respectively, where for the GaInAs/ GaInAsP/InP system the intervalence band absorption and nonradiative recombinations have been assumed to be the same as those obtained for bulk crystals experimentally. These results show the possibility of remarkable reduction in the laser threshold by the quantum-box structures.
British Journal of Cancer | 2003
Shohei Tanaka; Takaaki Akaike; Jun Fang; Toru Beppu; Michio Ogawa; Fumio Tamura; Yasuyuki Miyamoto; Hiroshi Maeda
Induction of haem oxygenase-1 (HO-1) may provide an important protective effect for cells against oxidative stress. Here, we investigated the mechanism of cytoprotection of HO-1 in solid tumour with a focus on the antiapoptotic activity of HO-1. Treatment of rat hepatoma AH136B cells with the HO inhibitor zinc protoporphyrin IX (ZnPP IX) or tin protoporphyrin IX resulted in extensive apoptotic changes of tumour cells both in vivo and in vitro. Caspase-3 activity of the ZnPP IX-treated hepatoma cells increased significantly. Moreover, ZnPP IX-induced apoptosis was completely inhibited by simultaneous incubation with a specific caspase-3 inhibitor and was partially abrogated by bilirubin, a reaction product of HO. In vivo ZnPP IX treatment did not affect nitric oxide (NO) production and tumour blood flow. Western blot analyses showed that HO-1 expression in AH136B cells was strongly upregulated by NO donors, for example, S-nitroso-N-acetyl penicillamine and propylamine NONOate in vitro; conversely, it was remarkably reduced in vivo by pharmacological blockade of NOS. We conclude that HO-1 may function in antiapoptotic defense of the tumour, and thus it may have important protective and beneficial effects for tumour cells against oxidative stress induced by NO, which is produced in excess during solid tumour growth in vivo.
Japanese Journal of Applied Physics | 1985
Masahiro Asada; Yasuyuki Miyamoto; Yasuharu Suematsu
Gain is given theoretically for quantum-well wire lasers where electrons are confined one-dimensionally. Maximum gain is obtained for a quantum-well wire perpendicular to light propagation, due to anisotropy of the dipole moment. Although the density-of-states is infinite at subband edges, gain remains finite due to the intraband relaxation. Therefore, high gain can be obtained by reducing intraband scatterings. Gain in 100 A×100 A Ga0.47In0.53As/InP quantum-well wires is about twice that in 100 A thick conventional quantum-wells, and reduction of the laser threshold is expected.
IEEE Journal of Quantum Electronics | 1989
Yasuyuki Miyamoto; Yasunari Miyake; Masahiro Asada; Yasuharu Suematsu
The laser threshold of three-dimensional GaInAsP/InP quantum-box lasers is analyzed. The optimized quantum-box array laser structure for the lowest threshold current density at room temperature is obtained theoretically, taking into account the effect of carrier leakage. The lowest threshold current densities are 14, 27, and 61 A/cm/sup 2/ for 10, 20, and 40 cm/sup -1/ of cavity loss, respectively. The threshold current density is calculated, taking into account fluctuation in quantum-box size. The ideal structure of the quantum-box laser is discussed. It is pointed out that the modulation-doped structure looks promising for the suppression of carrier leakage. >
Japanese Journal of Applied Physics | 1987
Yasuyuki Miyamoto; Ming Cao; Yasushi Shingai; Kazuhito Furuya; Yasuharu Suematsu; K. G. Ravikumar; Shigehisa Arai
Light emitting from quantum-box structure by current injection was observed for the first time. GaInAsP/InP quantum-box structures were fabricated from one-dimensional quantum-well (quantum-film) structures grown by OMVPE. Holographic lithography, wet etching, and LPE regrowth techniques were employed. Three-dimensional quantum size effect was suggested by the wavelength shift of the light emission.
Applied Physics Express | 2013
Edward Yi Chang; Chien-I Kuo; Heng-Tung Hsu; Che-Yang Chiang; Yasuyuki Miyamoto
60 nm InAs high-electron-mobility transistors (HEMTs) with a thin channel, a thin InAlAs barrier layer, and a very high gate stem structure have been fabricated and characterized. The thickness of the channel, as well as that of the InAlAs barrier layer, was reduced to 5 nm. A stem height of 250 nm with a Pt-buried gate was used in the device configuration to reduce the parasitics. A high DC transconductance of 2114 mS/mm and a current-gain cutoff frequency (fT) of 710 GHz were achieved at VDS=0.5 V.
Applied Physics Express | 2011
Ryousuke Terao; Toru Kanazawa; Shunsuke Ikeda; Yoshiharu Yonai; Atsushi Kato; Yasuyuki Miyamoto
We have realized InP/InGaAs composite-channel metal–oxide–semiconductor field-effect transistors with both selectively regrown n+-InGaAs source/drain regions and Al2O3 as a gate dielectric. A 100-nm-long channel was fabricated by laterally buried regrowth in a channel undercut by metalorganic vapor phase epitaxy. The carrier density of the regrown layer was 2.9×1019 cm-3. A drain current Id of 1.34 mA/µm was achieved at a drain voltage Vd of 1 V and a gate voltage Vg of 3 V. A transconductance gm of 817 µS/µm at Vd = 0.65 V was also observed at the same time. The improvement in the subthreshold slope can be explained by the decrease in dielectric/semiconductor interface trap density.
Scientific Reports | 2016
Toru Kanazawa; Tomohiro Amemiya; Atsushi Ishikawa; Vikrant Upadhyaya; Kenji Tsuruta; Takuo Tanaka; Yasuyuki Miyamoto
2D materials are expected to be favorable channel materials for field-effect transistor (FET) with extremely short channel length because of their superior immunity to short-channel effects (SCE). Graphene, which is the most famous 2D material, has no bandgap without additional techniques and this property is major hindrance in reducing the drain leakage. Therefore, 2D materials with finite band gap, such as transition metal dichalcogenides (TMDs, e.g. MoS2 WSe2) or phosphorene, are required for the low power consumption FETs. Hafnium disulfide (HfS2) is a novel TMD, which has not been investigated as channel material. We focused on its potential for well-balanced mobility and bandgap properties. The higher electron affinity of Hf dichalcogenides compared with Mo or W chalcogenides facilitates the formation of low resistance contact and staggered heterojunction with other 2D materials. Here we demonstrate the first few layer HfS2 FET with robust current saturation and high current on/off ratio of more than 10^4.HfS2 is the novel transition metal dichalcogenide, which has not been experimentally investigated as the material for electron devices. As per the theoretical calculations, HfS2 has the potential for well-balanced mobility (1,800 cm2/V·s) and bandgap (1.2 eV) and hence it can be a good candidate for realizing low-power devices. In this paper, the fundamental properties of few-layer HfS2 flakes were experimentally evaluated. Micromechanical exfoliation using scotch tape extracted atomically thin HfS2 flakes with varying colour contrasts associated with the number of layers and resonant Raman peaks. We demonstrated the I-V characteristics of the back-gated few-layer (3.8 nm) HfS2 transistor with the robust current saturation. The on/off ratio was more than 104 and the maximum drain current of 0.2 μA/μm was observed. Moreover, using the electric double-layer gate structure with LiClO4:PEO electrolyte, the drain current of the HfS2 transistor significantly increased to 0.75 mA/μm and the mobility was estimated to be 45 cm2/V·s at least. This improved current seemed to indicate superior intrinsic properties of HfS2. These results provides the basic information for the experimental researches of electron devices based on HfS2.
IEEE Electron Device Letters | 2007
Chia-Yuan Chang; Heng-Tung Hsu; Edward Yi Chang; Chien-I Kuo; Suman Datta; Marko Radosavljevic; Yasuyuki Miyamoto; Guo-Wei Huang
An 80-nm InP high electron mobility transistor (HEMT) with InAs channel and InGaAs subchannels has been fabricated. The high current gain cutoff frequency (ft) of 310 GHz and the maximum oscillation frequency (fmax) of 330 GHz were obtained at VDS = 0.7 V due to the high electron mobility in the InAs channel. Performance degradation was observed on the cutoff frequency (ft) and the corresponding gate delay time caused by impact ionization due to a low energy bandgap in the InAs channel. DC and RF characterizations on the device have been performed to determine the proper bias conditions in avoidance of performance degradations due to the impact ionization. With the design of InGaAs/InAs/InGaAs composite channel, the impact ionization was not observed until the drain bias reached 0.7 V, and at this bias, the device demonstrated very low gate delay time of 0.63 ps. The high performance of the InAs/InGaAs HEMTs demonstrated in this letter shows great potential for high-speed and very low-power logic applications.
Japanese Journal of Applied Physics | 1984
Shigeo Sugou; Atsuhi Kameyama; Yasuyuki Miyamoto; Kazuhito Furuya; Yasuharu Suematsu
The conditions required for the growth of GaInAsP/InP by organometallic vapor-phase epitaxy (OMVPE) covering the available bandgap wavelength of 1.3–1.6 µm were obtained experimentally with a carefully-arranged experimental set-up. The precision required in controlling the gas flows and temperatures for lattice matching is discussed. The relations between alloy compositions and source gas flow ratios were investigated, as well as p-n junctions. Lasing operation at a wavelength of 1.58 µm was achieved with GaInAsP/InP grown under these growth conditions.