The photorefractive effect at large modulation depth in semiconductors with multiple defect levels

The photorefractive effect in semiconducting mate- rials with multiple defects is studied in the case of modulation depth m = 1. The basic equations are Poisson's equation and the continuity equations for electrons, holes and occupied defect levels. They include all recombination and optical generation mechanisms between the defect levels and valence and conduc- tion bands. Their explicit numerical solution yields microscopic quantities such as space- and time-dependent electrical field profiles, carrier concentrations, as well as generation and re- combination rates. The fundamental Fourier component of the electric field yields the two-wave-mixing gain. Application is made for InP with two levels in the forbidden gap, for which steady-state and transient resulting quantities are shown. The re- sulting features at large modulation depth are of non-sinusoidal shape. Due to the complexity of the system, the final results strongly depend on all parameters intervening in the models used, as is illustrated for several typical cases.