The evolution of the photoinduced space charge and electric field distribution in photorefractive sillenite (Bi12GeO20, Bi12SiO20) crystals

Abstract

The paper reviews experimental and theoretical studies of the generation of photoinduced space charges and electric fields in sillenites. A. method is described of direct field distribution measurements on noncentrosymmetric crystals which is based on using the linear transverse electro-optic effect. The principal types of local centers and electronic transitions in sillenites are considered. Field evolution measurements are presented for various conditions of crystal photoexcitation. A theoretical discription is given of a sufficiently general charge transfer model involving the photogeneration of free carriers, their drift and trapping throughout the depth of the material. The calculations presented describe the field evolution under different conditions, in particular, for nonuniform carriers generation. The most interesting case is probably that of uniform generation which results in an unusual phenomenon, namely, space charge stratification under the screening of the external field. It consists in the formation of a multilayer variable-sign space charge structure with its layers moving against the carrier drift. The results of these studied may be used in the development of space-time light modulators and calculation of their characteristics.