Takao Kawamura

Photocurrent multiplication in amorphous silicon carbide films

The photocurrent multiplication reaching 300 times was recently observed in amorphous silicon carbide (a‐SiC:H) films using a simple cell configuration of SnO2/a‐SiC:H/Au. This phenomenon, which appeared only under the irradiation of bulk‐absorbed red light, is not due to Avalanche effects, but is thought to result from electron tunneling from SnO2 to a‐SiC:H film through a thin insulating thin silicon oxide layer formed at the a‐SiC:H/SnO2 interface in a high electric field built up by the photoaccumulated space charges of trapped holes near the interface.

Electrophotographic Properties of RF Glow Discharge-Produced Amorphous Si: H Film

Amorphous silicon film with extremely high dark resistivity, 1013–1014 ohm-cm, at room temperature is prepared for the first time by glow discharge decomposition of SiH4 with suitable doping by B2H6 and a slight content of oxygen. The a-Si: H film exhibits an excellent photoconductive sensitivity in visible wavelength range. Room temperature electron and hole drift mobilities are found to be almost the same in a-Si: H film deposited at 200°C of the substrate temperature and 10-3 B2H6/SiH4 doping gas ratio. These unique properties of a-Si: H films are utilized for bi-chargable monolayer electrophotographic photoreceptor, and positive and negative reproduced images have been firstly demonstrated by utilizing a-Si: H deposited drum.

Initial transient phenomena in the plasma decomposition of silane

Abstract Initial transient phenomena in the plasma decomposition of SiH 4 were investigated by measuring optical emission intensities and some properties of deposited a-Si:H interface layer. The variations of emission intensities from SiH and H depended on the consumption degree of SiH 4 . The deposition rate, hydrogen content, hydrogen bonding states and photoluminescence spectra of the a-Si:H interface layer were found to correlate strongly to the initial transient state of plasma and to differ from those of a bulk deposited in the steady state of plasma, especially at high consumption degree of SiH 4 .

Acoustic‐surface‐wave convolver using nonlinear interaction in a coupled PZT‐Si system

Efficient acoustic‐surface‐wave convolution, using 14.5‐MHz Bleustein‐Gulyaev waves, has been observed in a coupled PZT‐Si system. It has been found that the magnitude of the phenomenological nonlinear coupling constant of the convolver was four times as large as that of the basal plane of PZT‐8. The convolution output was controlled by the application of a voltage of several tens of volts.

A study of initial transient phenomena in the chemical vapor deposition process using silane plasma

Initial transient phenomena in the plasma deposition of hydrogenated amorphous silicon (a‐Si:H) film from SiH4 has been studied in terms of an origin and an influence on the device fabrication. The initial transient state (ITS) of plasma over the time ranging from 2 to 40 s is observed as variations of optical emission intensities from SiH and H rather than as double probe currents. A simple model shows that this is caused mainly by the variation of the SiH4 concentration at relatively high rf power as well as at a low SiH4 flow rate. The variation of electron energy distribution is also discussed as a dominant origin at low rf power and high SiH4 flow rate. The predischarge method by which the SiH4 concentration is controlled just before a main discharge is proposed in order to reduce the ITS. A strong influence of the ITS on the field‐effect response of the thin‐film transistor is observed and can be avoided by the predischarge method.

Heteroepitaxial growth of GaAs on sapphire substrates by a three-step method using low pressure MOCVD

Abstract Single crystal films of (111)GaAs have been grown onto (0001)Al 2 O 3 substrates by a low pressure MOCVD method. Using a three-step growth procedure, high quality heteroepitaxial growth of GaAs has been achieved by using an annealed buffer layer of ≈ 40 nm in thickness deposited on the substrate. Gallium arsenide films grown at a temperature of 620°C have a mirror-like surface morphology. Silicon-doped GaAs films exhibit n-type conductivity and typically an electron mobility of 4000 cm 2 /V ·s and a carrier concentration of ≈ 4 × 10 16 cm −3 at room temperature for a film thickness of 6 μm.

High-rate deposition of photosensitive a-SiC:H using a carbon source of C2H2

Abstract A high-rate deposition around 10μm/h of a-SiC:H films with band gaps of 2.0–2.1eV and with high photosensitivity exhibiting a conductivity change more than 10 4 of magnitude under illumination with 50μW/cm 2 in intensity is investigated using a glow discharge in SiH 4 C 2 H 2 H 2 mixture gas. This enables to make a photoreceptor with lower dielectric constant than that of a-Si:H films. It is also shown that the C 2 H 2 based gas system has a high efficiency of the carbon incorporation into the films.

Dark decay of surface potential: measurement of the density of localized states in highly resistive amorphous silicon alloys

Abstract An analysis is made of the depletion-discharge process in amorphous semiconductors exhibiting the Poole-Frenkel effect by considering the exponentially distributed emission states. It is shown that this new model selfconsistently interprets experimental observations and enables to estimate the density of localized deep states for a-Si:H:F and a-SiC:H films with resistivity higher than 1013 ωcm.

Dynamic Mechanism of Fast Switching in Light Valve Using Liquid Crystal

A light valve using a liquid crystal previously developed by the authors has a fast switching time of less than 1 ms. The fast switching mechanism of the value is studied theoretically in terms of the static characteristics of light transmission and the transient behavior of the cooperative angular variation of molecules submitted to an electric field. The variation in the light transmission is well explained by an analysis using optical anisotropy. The dynamic mechanism of the fast switching time is also interpreted by the principle of energy conservation related to the elastic, dielectric and viscous torque of the liquid crystal. The analytical results of the static and dynamic characteristics agree well with the experimental results.

High-Rate Deposition of a-Si: H Film Using the Decomposition of Mono-Silane

High-rate deposition technique of a-Si: H films for an electrophotographic photoreceptor using a glow discharge decomposition of SiH4 is described. The deposition parameters are optimized on the basis of results that the emission intensity ratio of the species H to SiH in the plasma is a function of the rf power and flow rate of SiH4 by which a hydrogen bonding state in the resultant film is controlled. An a-Si: H film with a suitable hydrogen bonding state for excellent electrophotographic properties is prepared at the high deposition rate of 5 µm/h. It is also found that the deposition rate is proportional to the emission intensity of SiH.