Electronic and optical properties of a-Si_1-xC_x films prepared from a H₂-diluted mixture of SiH₄ and CH₄

Abstract

This paper deals with the electronic and optical properties of a-Si_1-xC_x films deposited by glow-discharge decomposition of SiH₄ and CH₄ mixtures, in most cases with H₂ dilution. These results complement the structural and compositional data on the same specimens reported in the preceding paper.

A systematic investigation of optical absorption, dark conductivity, photoconductivity and H evolution has been carried out as a function of the carbon content of specimens prepared with and without H₂ dilution. It is shown that the former leads to a significant increase in the photosensitivity of specimens having optical gaps of up to 2.1 eV, in agreement with the work of Matsuda and co-workers. Further support for the improvement in electronic properties produced by H, dilution is obtained from density-of-states measurements, using the space-charge-limited current technique, and from photothermal deflection spectroscopy results, both of which show a significant decrease in the density of deep defect states. This is accompanied by a reduction in the Urbach edge parameter E ₀. Comparison of the H₂ evolution spectra suggests that H, dilution during deposition produces a denser network structure with fewer voids, which results from the increased surface mobility of the adsorbed radicals during film growth.