Yoshinori Ema

Formation and properties of In‐doped high‐conductivity CdS film

High dark‐conductivity CdS films have been prepared by coevaporation of CdS and In and the physical properties of the films were investigated. The dark conductivity of the films prepared at room ranged from 10−1 to 103 S cm−1. Analyzing the film structure by x‐ray analysis, it was found that the In atoms were doped substitutionally into the Cd site of a CdS crystallite at a low concentration In doping stage and then doped interstitially into the CdS crystallite at a high concentration In doping stage. In the carrier density versus the doped In concentration relation, the n‐type characteristic was found. This was explained by the two In doping processes described above. Further, the negative temperature dependence of the carrier density was detected in the very high‐concentration In‐doped samples. We used an explanation similar to the one given by Hung and Gliessman [Phys. Rev. 96, 1226 (1954)], that is, by using a tentative model in which the substitutionally doped low concentration In atoms form a shallo...

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.

Formation and properties of In‐doped high‐conductivity CdSe evaporated film

High dark‐conductivity CdSe films have been prepared by coevaporation of CdSe and In, and the physical properties of the films were investigated. The dark conductivity of the films at 25 °C ranged from 0.68 to 3800 S cm−1. The conductivity type was n‐type and In was found to act as the donor in CdSe films.The film structure was of hexagonal zinc sulfide type with a preferential orientation of the (002) planes parallel to the substrate. Analyzing the film structure in detail by x‐ray analysis, it was found that the In atoms were doped substitutionally into the CdSe during the low‐concentration doping stage and then doped interstitially during the high doping stage.

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.

Automatic modelling of reaction systems using genetic algorithms and its application to chemical vapour deposition processes: advanced utilizations of simulators for chemical systems

The identification of appropriate reaction models is very helpful for developing chemical vapour deposition (CVD) processes. We introduced novel algorithms to analyse experimental data from CVD processes and identify reaction models automatically using genetic algorithms (GAs). The reaction models, which consist of various deposition species and gas-phase and surface reactions, were determined both quantitatively and qualitatively, based on chemical kinetics. The GA modelling algorithm consists of a process for calculating the predicted results from the reaction model candidates and a process for modifying the candidates by use of the difference between experimental and predicted results. We demonstrate the validity of this approach to successfully identify the appropriate reaction models from synthetic experimental data and real experimental data obtained during thermal CVD of tetraethylorthosilicate.

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.

Formation and properties of vacuum-evaporated high conductivity n-type CdTe films

Abstract High dark conductivity CdTe films have been prepared by co-evaporating CdTe and cadmium. The structural, electrical and optical properties were investigated. The dark conductivity of the film increased monotonically with an increase in the amount of co-evaporated cadmium. The highest dark conductivity of the films obtained in this experiment was 1.4x10 -2 Ω -1 cm -1 . The film structure was of the zinc blende type with a preferential orientation of the (111) planes parallel to the substrate and fibrous. The crystallinity of the films was similar to that of films without cadmium doping. The dark conductivity vs . the reciprocal temperature characteristics showed regular aspects. High dark conductivity films will be useful for CdTe thin film device applications.

Formation and properties of very high-conductivity CdTe film made by evaporation

Very high‐conductivity n‐type CdTe films with large crystallite size were prepared by vacuum coevaporation of CdTe and Cd and the electrical properties and the structure were investigated. The highest dark conductivity at room temperature of the film obtained was 6.5×103 S cm−1. The conductivity decreased with the increase of the ambient temperature. The electron concentration increased and the mobility decreased with the temperature. The film was a polycrystalline hexagonal phase and the crystallite size was a few tens of μm.

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.

Ge doping effect on properties of AgInSe2 thin films

The effect of Ge doping on the properties of AgInSe2 thin films has been investigated by the co-evaporation of AgInSe2 alloy chunks, Se and Ge on Corning 7059 glass substrates. Samples were nearly stoichiometric and contained very small amounts of Ge. They showed a highly [112]-oriented chalcopyrite structure, good optical transmittance spectra in the IR region (λ=1-2.6 µm) and an increase of n-type conductivity compared with the nondoped sample. Raman scattering suggested that the doped Ge atoms replaced some of the In atoms in the chalcopyrite structure. The Ge-doped sample grew uniformly from the beginning of film deposition.