A.c. photoconductivity and optical properties of bulk polycrystalline and amorphous In x Se1?x thin films

Abstract

The a.c. photoconductivity of bulk polycrystalline In x Se1−x and the optical properties of amorphous In x Se1−x thin films were investigated. The effect of heat treatment on the absorption coefficient of InSe thin films was also studied. The spectral response of the photoconductivity of polycrystalline In x Se1−x related to the near-edge absorption spectrum, shows a well-defined maximum corresponding to the width of the forbidden gap. Polycrystalline In x Se1−x realizes the behaviour of photoconductors which are sensitive in a spectral range between 400 and 1700 nm. Optical absorption of amorphous In x Se1−x thin films was recorded as a function of photon energy and the data were used to deduce the value of optical energy gap of the films. It was found that the optical energy gap decreased with increasing indium content in both bulk polycrystalline and amorphous thin films. The effect of heat treatment on the optical gap of the film has been interpreted in terms of the density of states model of Mott and Davis.