We investigated the process of Pb center generation during silicon oxidation following oxygen termination on a clean Si surface, based on which we discuss the microscopic origin of Pb centers. We constructed a UHV-ESR system which enabled measurements to be carried out at a low temperature of around 100 – 120 K, and used the system to study the Si(111)-7×7 surface after slight exposure to O2. Based on the observed ESR spectra, we discuss the electronic structure of the Si(111)-7×7 surface.

Correlation between the gas phase species in silane plasma measured by mass spectrometry and the properties of hydrogenated amorphous silicon (a-Si:H) films deposited by plasma enhanced chemical vapour deposition (PECVD) has been investigated. We have especially been interested in the higher-order silane related species in the plasma, whose contribution to the film growth is considered to be the cause of light-induced degradation in the film quality, especially at high growth rate. In this study, we varied excitation frequency, gas pressure and power density to vary the growth rates of a-Si:H films ranging from 2 Å/s to 20 Å/s.

Molecular density ratio of trisilane, representative of higher silane related radicals, to monosilane has shown a clear correspondence to the fill factor after light soaking of Schottky cells fabricated on the resulting films.

The role of hydrogen atoms in the formation process of hydrogenated microcrystalline silicon (μc-Si:H) by plasma enhanced chemical vapor deposition method has been investigated. Under the present conditions, the etching and the permeation of hydrogen atoms in the subsurface region do not cause the crystallization. The kinetics study of surface morphology and structure in the initial growth of μc-Si:H on an atomically flat substrate indicates that the onset thickness of island coalescence reduced under μc-Si:H formation condition. The results support the ‘surface diffusion model’ in which the surface diffusion of film precursors is enhanced by the sufficient hydrogen coverage of surface and by hydrogen atom recombination energy on the growing surface of the film.

Amorphous silicon films and solar cell i-layers were prepared from dichlorosilane(DCS) by ECR- and VHF-CVD. The hydrogen content, the chlorine content and the band gap could be controlled by varying argon and hydrogen dilution. The interaction of energetic and reactive plasma species with substrates and other previously deposited layers was studied. DCS, ECR-CVD causes darkening of TCO substrates even when buffer layers and/or doped layers were previously deposited by RF-CVD. Therefore n-i-p solar cell structures were prepared on NiCr and subsequent p-i-n solar cells were prepared with VHF-CVD which did not causeTCO reduction or other reactions in previously deposited amorphous layers. Preliminary results indicate that the VHF-CVD solar cells are at least as stable as standard amorphous silicon solar cells.

Previously it was shown that high quality wide gap hydrogenated amorphous silicon material could be prepared by a layer-by-layer technique involving hydrogen chemical annealing. Using this wide gap material, high electric field, n-i-p diode devices were fabricated. Reverse bias dark current was suppressed by optimization of the n-layer doping level (250ppm) and the thickness (2000Å). Working vidicon type device were prepared, tested, and optimized by further reduction in the high reverse bias leakage current. Vidicon devices showed very promising performance; however, at the present stage of development some point defects were observable at the highest reverse bias voltages probed (∼-6×105 V/cm).

Hydrogenated amorphous silicon (a-Si:H) films were prepared by a layer-by-layer (LBL) argon treatment technique. Thin amorphous silicon layers are first deposited and then treated by Ar. Thick films are built up by repeatedly the process many times. By reducing the deposition rate during deposition time (T, sec), a-Si:H with the gaps narrower than 1·55eV were prepared at substrate temperature lower than 300°C. These narrow-gap films contained less than 2 at.% hydrogen and had rigid Si network. Also, these narrow gap films exhibited good light soaking stability.

Silicon thin films were prepared by “Chemical Annealing” where the deposition of thin layer (<3 nm thick) by RF glow discharge of SiH4 and the treatment with hydrogen atoms (H) or triplet state of argon (3Ar) were repeated alternatating. Consequently, wide gap a-Si:H with the gap of 2.1 eV was made by H-treatmentat rather low substrate temperature (Ts<150 °C), while a-Si:H with the gap narrower than 1.6 eV was obtained by the treatment with 3Ar at high Ts (>300 °C), resulting from the release of excessive hydrogen. Both the wider or the narrower gap films exhibited low defect density lower than 1016 cm−3 and obvious improvements in the stability for light soaking.

Hydrogenated amorphous silicon (a-Si:H) with a gaps narrower than 1.7 eV were made by repeating the deposition of a thin layer (1–3 nm thick) and the treatment of growing surface with a mixture of H and Ar*. Crystallization induced by permeation of hydrogen into the subsurface at high substrate temperature (>200C) was efficiently prevented by treating with a mixture of H and Ar*. The activation of growing surface may arise from releasing a part of hydrogen on surface by treating with Ar*. High quality a-Si:H films containing hydrogen of 3 atom % with a gap of 1.6 eV were made by chemical annealing with a mixture of H and Ar*.

High quality wide gap hydrogenated amorphous silicon has been prepared using the chemical annealing technique. It was possible to prepare materials with band gaps ranging 1.8 to 2.1 eV by varying the preparation parameters. Low defect densities less than (3–8) x 1015 cm-3 could be maintained over the entire band gap range. Improved stability for light soaking was also observed in the wide gap materials.