Recombination in amorphous semiconductors

Abstract

Recombination mechanisms for electrons and holes in chalcogenide glasses and amorphous silicon are discussed. In chalcogenides the model of charged defects is assumed to hold. Recombination can occur either radiatively by an electron-hole pair at a defect, or nonradiatively by self-trapping of a free exciton or by tunneling between defects. In amorphous silicon self-trapping of excitons is insufficient to give nonradiative recombination and the absence of this mechanism accounts for many of the differences between Si and chalcogenides. The experimental conditions under which each recombination mechanism should apply are described. In particular, the photoconductivity recombination is shown to be by tunneling between electrons and holes trapped at charged defects, which also determines the extent to which chalcogenides exhibit photoluminescence fatigue and induced ESR.