Keiji Fujibayashi

Degradation of Gallium Arsenide Crystals by the Cold-Working Treatment (Abrasion)

The effect of the cold working treatment on the characteristics of GaAs crystals was studied. Abrasion and subsequent heat treatment of the crystals decrease the carrier concentrations and increase the breakdown voltages. After abrading and subsequent heat treatment, the increase in etch-pit density in the crystals was observed. It is supposed that the degradation of the crystals was related to the generation of dislocations during such treatments.

Saturation of optical degradation in a-Si:H films with different morphologies

The saturation effect of the optical degradation in hydrogenated amorphous silicon films (a-Si:H) deposited at various temperatures Ts has been studied by means of photoconductivity measurements. It was confirmed that the saturation is mainly related to the simultaneous annealing at a higher light-soaking temperature T1 (?20?C) as well as the depletion of the weak Si-Si bonds at lower T1 (?0?C). The weak bond density (1016?1018/cm3) estimated from the low-temperature saturation effect decreases with increasing Ts corresponding to the growth of Si clusters.

Preparation of a-Si:H Films Resistive to the Staebler-Wronski Effect

Undoped a-Si:H films with much reduced sensitivity to the optical degradation (Staebler-Wronski effect) were prepared by the combination of conventional plasma CVD starting from pure silane and subsequent lamp annealing at 450~500°C for 10~15 min in nitrogen. It was observed that both the photoconductivity and the ratio of photoconductivity to dark conductivity was not appreciably degraded by the lamp annealing, indicating the absence of the unintentional doping which often appears in a-Si:H prepared by conventional plasma CVD with high substrate temperature and in µc-Si:H from highly diluted SiH4 with H2.

Optical Degradation of a-Si:H films with Different Morphology

The optical degradation (Staebler-Wronski (SW) effect) of a-Si:H films prepared by plasma CVD has been studied in connection with the morphological inhomogeneity of the films. The relative degradation rate of cubic photoconductivity α widely varied with deposition substrate temperature Ts and had its maximum at Ts=200~250°C. In the films of both the lower and higher Ts, α decreased due to the increase of stable dangling bonds in the former and the decrease of weak bonds in the latter. The SW effect was hardly observed in µc-Si:H deposited from highly diluted silane with hydrogen.

GaxIn1-xSb Gunn Diodes

GaxIn1-x Sb single crystalline layers grown on GaSb and InSb substrates are prepared in a whole composition range by a liquid phase epitaxial technique. Ga0.82In0.18Sb Gunn diodes are fabricated and preliminary measurements of the oscillator performance in a pulsed operation are obtained. The highest values of maximum efficiency and peak output power are 9.2% at 2.6 GHz and 950 mW at 1.9 GHz, respectively.

Optical Degradation and Morphology in a-Si:H

The relationship between the optical degradation and the morphology of hydrogenated amorphous silicon (a-Si:H) films was studied through the analysis of the annealing processes. The annealing of optically induced metastable dangling bonds can be explained in terms of the first and the second order reactions with dispersive hydrogen diffusion for the films deposited at lower and higher temperature, respectively. The activation energy of the annealing was estimated to be 0.8 eV with a small distribution in both cases. Optically enhanced annealing was first observed. It was found by DLTS and CT measurements that the density of hole trap located at Ev+0.6 eV was remarkably decreased by the light soaking, accompanied by the simultaneous increase of electron trap at Ec-0.7 ∼ Ec-0.9 eV due to the dangling bonds. These experimental facts support the view that the hole trap corresponds to the weak bonds, which convert to the metastable dangling bonds by light soaking.