A multiple-trapping model with optical bias

The transient response of an illuminated (‘optically biased’) semiconductor to a small photoexcitation impulse is calculated by linearizing the multiple-trapping model. Both the photocurrent and photo-induced absorption responses are treated, including the effects of finite trap occupancy and of monomolecular or bimolecular recombination processes. Specific solutions are presented for exponentially distributed traps, and a simple classification of these transient responses based on a thermalization criterion is advanced. The numerical and analytical solution procedures used are, in principle, exact and may be used to calculate the transient response for arbitrary trap distributions. These solutions are compared with the approximate solutions obtained using the time-dependent demarcation-energy technique. Procedures for using the results to obtain the model parameters from experimental transient-response measurements are given.