Belarusian State University, Belarus

Crystals of the sillenite family are photorefractive crystals with a wide band gap, placing them among the wide-gap semiconductors. However, these crystals contain a large number of impurities and structural defects, resulting in a complex energy level system in the band gap. The main components of this energy level system are donor and acceptor impurities, as well as structural defects that act as acceptor traps. To describe band transfer processes in sillenite crystals, Kukhtarev's system of equations was used, supplemented by the inclusion of shallow traps. This system includes equations describing changes in the concentration of ionized donors, shallow traps, and electrons in the conduction band, as well as Poisson's equation, which relates these concentrations to the electric field. Short-term spatially modulated radiation was used as the excitation source for solving this system, corresponding to the interference pattern of two plane waves. In the first stage, short-term, powerful pulsed excitation occurs. The number of ionized donors and free electrons increases. In the second stage, diffusion and drift lead to the formation of a specific electron distribution in the conduction band, which generates an internal field. In the next stage, electron relaxation into small traps occurs, and at the end of this stage, the population of small traps will match the electron distribution at the beginning of the stage. In the fourth stage, due to the relatively rapid relaxation, which dominates the thermal excitation of electrons in small traps, the spatial profile of the population of small traps will level out. And finally, at the last stage, relaxation of electrons to ionized donors will occur with the complete disappearance of internal fields.