Thickness dependence of electrical and optical properties and E.S.R. in undoped a-Si: H

Abstract

The thickness dependence of photo- and dark-conductivities, E.S.R., optical absorption and hydrogen vibrational spectra have been investigated for undoped glow-discharge a-Si: H films. The measurements of the photoconductivity were carried out at wavelengths of 5145 and 6328 and 8500 Å. Reductions of photoconductivity and activation energy for dark conductivity, and increases of E.S.R. spin density, the optical energy gap and hydrogen concentration, were found to occur for decreasing film thickness. These results are analysed in terms of a two-layer model and, as a consequence, by the existence of high densities of recombination and E.S.R. centres near the surface(s). The effects of plasma hydrogenation on the photoconductivity and E.S.R., and the photo-induced change of the photoconductivity are discussed in terms of the two-layer model. The photoinduced change is interpreted as a bulk rather than a surface effect.