Analysis of Photoconductivity in Amorphous Chalcogenides

Starting with standard semiconductor recombination statistics and a generalized distribution of localized states within the mobility gap of an amorphous semiconductor, a model for photoconductivity has been developed. Consistency with experimental phenomena requires the inclusion in this model not only of the traditional nonlocalized-to-localized state recombination transitions, but also of two types of localized-to-localized state recombination transitions: (i) from states nearer than a critical energy to the conduction edge, to similar states nearer than a critical energy to the valence edge; (ii) from states near the mobility edges to states near the thermal equilibrium Fermi level. Such a model has general applicability to a variety of different types of amorphous chalcogenides, encompasses previously reported variations of photoconductivity with intensity and temperature, and provides a way of estimating the characteristic parameters of localized states in these materials. Quantitative application of the model is made to photoconductivity data for three amorphous chalcogenides.