ELECTRONIC AND OPTICAL-PROPERTIES OF A-SI1-XCX FILMS PREPARED FROM A H2-DILUTED MIXTURE OF SIH4 AND CH4

This paper deals with the electronic and optical properties of a-Si1 _XCX 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 H2 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 21 eV, in agreement with the work of Matsuda and coworkers. Further support for the improvement in electronic properties produced by H2 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 E0. Comparison of the H2 evolution spectra suggests that H2 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. © 1990 Taylor & Francis Ltd.