The impact of deep levels on the photocurrent transients in semi-insulating GaAs

The photocurrent transients, IPC(t), were studied in semi-insulating (SI) GaAs during a low-temperature (low-T) illumination. Unusual transients were explained by the model, relating IPC(t) to the deep levels/traps and their occurpancy. Such traps were actually detected and characterized by the independent measurements of the thermally stimulated currents (TSCs). The processes of the generation, recombination, and capture were described by a set of coupled differential equations and solved numerically. The IPC(t), calculated without any free parameter, well reproduced (through eight orders of magnitude) the experimental transients over a wide range of the photon energies and intensities. The best-fit parameters agreed well with those determined from the TSC measurements.