Photocurrent decay from the steady-state in thin film hydrogenated amorphous silicon: Numerical simulation analysis of experimental results

Starting from the multiple trapping rate equations that define the non-equilibrium concentrations of electrons and holes in extended states, the experiment of photocurrent decay from the steady-state is examined. A system of non-linear coupled differential equations is solved to get the temporal evolution of the occupation functions and the carrier concentrations after cessation of the illumination. Different expressions proposed in the literature to evaluate the carrier lifetimes from the photocurrent decay data are critically examined. Measurements performed on a series of hydrogenated amorphous silicon samples deposited at different substrate temperatures are reproduced by the simulations. It is found that the response time determined from the photocurrent initial rate-of-decay provides an excellent estimation of the free lifetime of the majority carrier, provided the decay is recorded from sufficiently short times. It is also found that the common recombination lifetime can also be estimated from the photocurrent decay data.