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Dive into the research topics where H. Ishikura is active.

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Featured researches published by H. Ishikura.


Applied Physics Letters | 2000

Stable avalanche-photodiode operation of ZnSe-based p+–n structure blue-ultraviolet photodetectors

H. Ishikura; Tomoki Abe; Nariyuki Fukuda; Hirofumi Kasada; Koshi Ando

A high-field operation of p+–n structure blue-ultraviolet photodetectors has been studied using ZnSe-based II–VI wide-band-gap compound semiconductors grown by molecular-beam epitaxy (MBE). With an improved crystal quality on macrodefects (dislocations and stacking faults) during an initial MBE growth as well as an optimized device structure including a complete superlattice ohmic-contact layer, a stable high electric-field operation up to 8×105 V/cm is established. It is demonstrated that the p+–n ZnSe photodiodes have shown a stable avalanche-photodiode operation with a large avalanche gain of G=60 in the blue-ultraviolet region at room temperature.


Physica Status Solidi B-basic Solid State Physics | 2002

Highly Efficient Blue–Ultraviolet Photodetectors Based on II–VI Wide-Bandgap Compound Semiconductors

Koshi Ando; H. Ishikura; Y. Fukunaga; T. Kubota; H. Maeta; Tomoki Abe; H. Kasada

II-VI ZnSe (binary) and ZnSSe (ternary) widegap compound semiconductor based photovoltaic devices (p-i-n and avalanche photodiodes (APDs)) are developed for the blue-violet (460-400 nm) optical wavelength region by molecular beam epitaxial (MBE) growth. The ternary compound ZnSSe p-i-n structure photodiodes, grown with complete lattice matched condition on GaAs substrates, exhibit high external quantum efficiencies of 80-70% in the blue-violet optical region with extremely low dark currents (∼pA/mm 2 ), These diodes reveal stable and long-lived operation at 300 K. Also presented is ZnSe and ZnSSe based blue-violet APD devices, fabricated by precise defect control and process techniques. This new device has revealed large signal gain (G) of G = 50 for ZnSe, and G = 60 for the ZnSSe APD device under high electric field strength of (0.8-1.1) × 10 6 V/cm. Important device parameters, ionization coefficients of photo-injected electrons and holes, and device stability are also discussed.


Japanese Journal of Applied Physics | 1998

Persistent Photoconductivity (PPC) and Related Deep Metastable Center in MBE Grown p-Type ZnMgSSe

Tsutomu Yamaguchi; Koshi Ando; Keiichi Koizumi; Hideyuki Inozume; H. Ishikura; Tomoki Abe; Hirofumi Kasada

A persistent-photoconductivity (PPC) effect and the related deep metastable centers have been investigated for a p-type ZnMgSSe quaternary system grown by molecular beam epitaxy. A low temperature photo-excitation revealed a marked PPC effect in nitrogen doped p-type Zn1-xMgxSySe1-y (0.05<x<0.18, 0.08<y<0.2) with an exponential temperature dependence of the carrier decay time constant: τ(T) = τ0 exp (-490±50 meV/kT). It is also confirmed that the low-temperature photo-excitation has caused a new deep metastable hole trap center with thermal hole activation energy of 650 meV. This metastable deep center is evidenced to be responsible for the observed PPC effect.


Journal of Crystal Growth | 2000

Optimization of ZnSe/ZnTe superlattice structured p-contact for ZnSe-based optical devices

Tomoki Abe; H. Ishikura; Yuki Saomoto; Keizo Goto; Koichiro Masuda; Toru Shirai; Hiroshi Yamada; Shingo Kuroda; Hirofumi Kasada; Koshi Ando

We have optimized the structure of ZnSe/ZnTe superlattice electrode by comparison between experimental characteristics and theoretical calculations. Quantum levels in ZnSe/ZnTe superlattice and tunneling carrier densities are evaluated by using finite element method and transfer matrix method, respectively. It is found that important parameters for the design of the superlattice electrode are (a) high ground quantum level of hole, and (b) large tunneling carrier density. A new optimum structure with very high tunneling current density is proposed.


Physica Status Solidi B-basic Solid State Physics | 2002

High Efficiency and Long‐Lived Green and Blue Light Emitting Diodes Based on ZnSSe:Te Active Layer Grown by Molecular Beam Epitaxy

Hong Chan Lee; N. Kaneko; Masashi Watanabe; Y. Fujita; Tomoki Abe; H. Ishikura; Masahiro Adachi; H. Kasada; Koshi Ando

Bright green and blue light emitting diodes have been developed based on ZnSSe:Te active layer, with high crystal quality and a close lattice-match to GaAs substrate. The green LEDs exhibit a fairly long lifetime (>2000 h) at room temperature, which is attributable to the crystal-hardening effect by Te-doping. The devices show slow-mode degradation due to the gradual enhancement of microscopic defects in p-ZnMgSSe cladding layer. No detectable changes in dark-spot and dark-line formation due to macroscopic defects are observed during device operation.


Physica Status Solidi B-basic Solid State Physics | 2002

Blue‐Violet Avalanche‐Photodiode (APD) and its Ionization Coefficients in II–VI Wide Bandgap Compound Grown by Molecular Beam Epitaxy

H. Ishikura; Y. Fukunaga; T. Kubota; H. Maeta; Masahiro Adachi; Tomoki Abe; H. Kasada; Koshi Ando

We present II-VI wide bandgap semiconductor ZnSe and ZnSSe based blue-violet avalanche photo-diode (APD) operation grown on GaAs substrate by molecular beam epitaxy (MBE). Because of highly improved crystal quality of the active layer, the ZnSSe APD reveals stable and high avalanche gain (G ≥ 60) in the blue-violet optical region under high field operation condition (E = 1.15 x 10 6 V/cm) at room temperature (RT). High electric field induced ionization coefficients α (for electrons) and β (for holes) are determined as a function of electric field strength E(V/cm); α(E) = 1.7 × 10 7 exp (-4.9 × 10 6 /E) and β(E) = 3.7 × 10 6 exp (-4.0 × 10 6 /E).


Journal of Crystal Growth | 2000

High quantum efficiency blue–ultraviolet ZnSe pin photodiode grown by MBE

H. Ishikura; Nariyuki Fukuda; Masaki Itoi; Kazue Yasumoto; Tomoki Abe; Hirofumi Kasada; Koshi Ando


Journal of Crystal Growth | 2000

Demonstration of blue-ultraviolet avalanche photo-diodes of II–VI wide bandgap compounds grown by MBE

Tomoki Abe; H. Ishikura; Nariyuki Fukuda; Zaw Min Aung; Masahiro Adachi; Hirofumi Kasada; Koshi Ando


International Conference on II-VI Compounds | 2002

Blue-violet avalanche-photodiode (APD) and its ionization coefficients in II-VI wide bandgap compound grown by molecular beam epitaxy

H. Ishikura; Y. Fukunaga; T. Kubota; H. Maeta; Masahiro Adachi; Tomoki Abe; H. Kasada; Koshi Ando


International Conference on II-VI Compounds | 2002

High efficiency and long-lived green and blue light emitting diodes based on ZnSSe:Te active layer grown by molecular beam epitaxy

Hong Chan Lee; N. Kaneko; Masashi Watanabe; Y. Fujita; Tomoki Abe; H. Ishikura; Masahiro Adachi; H. Kasada; Koshi Ando

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