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An investigation was made of the plasma reflection of light and the results were used to find the effective mass of highly degenerate copper selenide,p>1020 cm−3, as a function of carrier concentrationp. The study of the temperature dependence of effective mass, electrical conductivity, thermoelectric power and Hall mobility carried out in the present work gives an idea of the nature of the valence bands in these materials.

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.