Toshiya Hayashi

Effect of Deposition Rate and Substrate Temperature on Properties of CdTe Film

The effects of the deposition rate and the substrate temperature on the structure and the electrical and optical properties of CdTe film evaporated on an Au-coated glass substrate were investigated, and the film quality is discussed here. It is shown that the crystalline size decreased with the deposition rate and increased with the substrate temperature, and that the stoichiometry of the film was best at the deposition rate of 17 A sec-1 at room temperature. At a lower deposition rate, the film became Cd-rich and n-type, while it became Te-rich and p-type at a higher deposition rate. The Cd content increased with the substrate temperature. The films deposited at lower rates were polycrystalline and those deposited at higher rates were amorphous. The film deposited at a rate of 17 A sec-1 –19 A sec-1 and a substrate temperature of 100°C showed the highest quality of all the films.

A Very-High-Conductivity of In-Doped CdTe Film

Very-high-conductivity CdTe films were prepared by co-evaporation of CdTe and In. The highest dark conductivity obtained was 103 S cm-1. It is shown that the highest conductivity film contains many In atoms doped interstitially into almost all wide space lattice points and forms a new crystal basis composed of Cd(0 0 0), Te(1/4 1/4 1/4) and In(1/2 1/2 1/2), (3/4 3/4 3/4). The interstitially doped In atoms were stable and did not move from the crystallite into the grain boundary, even when the film was heat-treated.

p-Si/n-CdS Heterojunction Solar Cells

p-Si/n-CdS heterojunction solar cells having CdS windows were fabricated by evaporating double layers of n-CdS films (n+-CdS layer on n-CdS layer) on p-Si single-crystal wafer. The electric and photoelectric characteristics were measured and discussed. Various preparation parameters affecting the cell characteristics were discussed and the best condition for preparation of cells was found. Open-circuit voltage, short-circuit current and conversion efficiency measured under sunlight of input power intensity of 45 mW cm-2 ware 510 mV, 15mA cm-2 and 11.3%, respectively.

In Doping in CdTe Film by Co-Evaporation of CdTe and In

High-dark-conductivity CdTe films have been prepared by co-evaporation of CdTe and In. The conductivity of the films prepared in this study ranged from 10-8 to 103 Scm-1. The film structure was of the zinc-blende type with a preferential orientation of the (111) planes parallel to the substrate. Analyzing the film structure by X-ray analysis, it was found that the In atoms were doped substitutionally into the CdTe during the low-concentration doping stage and then doped interstitially during the high-concentration doping stage. The properties of a very-high-conductivity film could be explained by adopting a new periodicity concept of the doped film using a tentative model.

Formation and Properties of Polycrystalline p-Type High-Conductivity CdTe Films by Coevaporation of CdTe and Te

Polycrystalline p-type high-dark-conductivity CdTe films have been prepared by coevaporation of CdTe and Te. The structural and electrical properties were investigated. The dark conductivity of the films at 300 K ranged from 6.32×10-8 to 3.41 S cm-1. The film structure was of the zincblende type with a preferential orientation of the (111) planes parallel to the substrate. The crystallinity was rather good. From the measurements of the carrier concentration versus ambient temperature characteristics, it was found that the high-conductivity p-type conduction of the films was due to the formation of Cd vacancies, acceptors resulting from the coevaporation of CdTe and Te. It is shown that the high-conductivity films obtained are suitable for p-CdTe/n-CdS solar cells.

Aging Effect of Capacitance and Related Effects in Au/a-Se/Al Structure

The contact between an a-Se and an Al electrode was found to show some characteristic features. When samples of the Au/a-Se/Al structure were kept in air, their capacitance first decreased and then increased. At the same time, their photocurrent and photovoltage increased gradually with time, and their spectral responses shifted. A chemical EMF appeared in the samples, also. The capacitance of the samples became voltage-dependent after a long time. These aging effects could be explained well by considering them to be the result of Se crystallization based on the migration of Al ions into Se assisted by the chemical reaction of Se and Al in moisture (H2O). The migration of Al ions and the structural change of the a-Se layer with time were confirmed by AES, RHEED and X-ray diffraction analyses. Al ions migrating into the Se layer are thought to act as nuclei for the crystallization of a-Se.