Hirofumi Kasada

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

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.

Microscopic defect induced slow-mode degradation in II–VI based blue–green laser diodes

Abstract We have studied the microdefect induced degradation mode in long-lifetime blue–green laser diodes (LDs) and light emitting diodes (LEDs) based on II–VI wide bandgap semiconductors. Microscopic deep defect centers in the LDs and LEDs are detected using mainly DLTS technique, coupled with ICTS methods. It is evidenced that a slow-mode degradation, commonly observed in dislocation-free LD devices, is caused by the generation and enhancement of microscopic deep centers during the device aging process. One possible degradation mechanism with a “carrier removal effect” is presented.

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

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.

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

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.

High Gain and High Sensitive Blue-Ultraviolet Avalanche Photodiodes (APDs) of ZnSSe n+-i-p Structure Molecular Beam Epitaxy (MBE) Grown on p-type GaAs Substrates

High gain and high sensitive blue-ultraviolet avalanche photodiodes (APDs) are developed using high quality ZnSSe n+-i-p hetero-structure grown on p-type GaAs substrates by molecular beam epitaxy (MBE). The short wavelength APDs have been realized by a new technique of interface superlattice buffers between p-GaAs and p-ZnSe hetero-interfaces, by which we have overcome large interface energy barriers (>1 eV: for hole-conduction) and unstable dark leakage currents. Utilizing a benefit of the n+-i-p structure on p-GaAs, the short wavelength APDs have been designed with an thin transparent n+ window layer ( 90) and high sensitivities of 5–3 A/W in blue-ultraviolet optical region under very low reverse bias condition of 33 V.

Decrease in Surface States on GaAs Metal-Semiconductor Field-Effect Transistor by High Temperature Operation

The decrease mechanism of plasma-induced surface states in a GaAs metal-semiconductor field-effect transistor (MESFET) during high temperature operation has been studied by means of high temperature operational tests, drain current transient analysis and three-terminal gate current measurements. The energy level of trapped electrons in the surface states distributes widely in the band-gap, and its activation energy does not change after decreasing the density of surface states. In order to decrease the surface states effectively, hot-carriers generated by accelerated channel electrons under high temperature operation are required.

ZnSe-based organic–inorganic hybrid structure ultraviolet avalanche photodiodes with long lifetime and its device integration

We have developed organic [poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS)]–inorganic [ZnSSe] hybrid structure ultraviolet avalanche photodiodes (UV-APDs) with a long device lifetime and integrated APD arrays. The active layer is ZnSSe grown by molecular beam epitaxy (MBE) and the window p*-type layer is PEDOT:PSS formed by the inkjet method. The device exhibits a lifetime of more than 100 d and an APD operation of more than 500 times. We integrated 3-element APD array separated only by a window spot of PEDOT:PSS. The present array device in the APD operation shows no detectable photosignal cross-talk between the neighboring APDs.

Analysis of GaAs/SiN interface states and hot carrier annealing effects in GaAs MESFET

We have analyzed in detail the disappearance phenomenon of the plasma induced interface states (GaAs/SiN) on GaAs MESFET by means of drain current transient, three-terminal gate current, optical beam induced current (OBIC) and light emission. The energy level of trapped electrons in the interface states distributes widely in the band-gap below the conduction band. The interface states decrease by high temperature operation keeping its energy level constant. It requires hot-carrier effects to decrease the interface states.

Tunable laser for sensing atmospheric transmission in the infrared region of 11 ∼ 16 µm

We succeeded in observing the continuously tunable, pulsed InSb SFR (Spin-Flip Raman) laser emission in the infrared region of 11∼16µm (11.4∼16.3µm) from only one InSb device, merely by adjusting the pumping wavelength (11 lines from the infrared NH3 laser) and the applied magnetic field (0∼80 kGauss).