Analysis and modelling of generation-recombination noise in amorphous semiconductors

We examine several analytical models with different predictions for noise associated with conductivity fluctuations in homogeneous thin film semiconductors. In one model, the noise spectrum is assumed to reflect separately the release times of groups of trapping centres in the material. In another, the trapping time into the whole distribution of traps is assumed to dominate, predicting that, in a material like a-Si:H, where trapping into tail states is of order 1 ps, the trapping component of the noise spectrum should be unobservable. Our own analytical approach includes weak coupling between traps via the extended states, which is most clearly demonstrated by use of an R–C equivalent circuit approach for the multi-trap system. We assess the models using a Monte Carlo simulation of the trapping, generation and recombination transitions, which automatically incorporates statistical features associated with these processes, and hence it is free of assumptions. Simulation results support our thesis, and verify that the same information is contained in the real part of the modulated photoconductivity spectrum.