The effect on recombination in amorphous semiconductors of transitions between localized states

An analysis is presented of the effects of transitions by electrons between localized states and from these states to recombination centres on the rate of recombination and the transient photocurrent in amorphous semiconductors such as a-Si: H. It is shown that if an effective capture cross-section is defined for the recombination centres to take account of the recombination from localized states, this cross-section is time-dependent, and so is not very useful except in steady-state experiments. The analysis is based on the use of average transition rates; the evaluation of these for a mean-field model system and for a model system that takes account of local microscopic inhomogeneities is considered. The results of calculations for these two systems are compared, in order to discover the nature of the effects produced by such inhomogeneities.