Photorefractive charge migration in BSO: A comparison of the band transport and hopping models

There is a continued interest in the charge transport mechanism for the photorefractive effect, particularly in the sillenites (BSO, BGO, BTO)1,2. There are two prevalent models for the photoexcited charge migration, namely, the band transport theory and the hopping model3. In this paper we present a detailed comparison of the hopping and band transport models. We place the hopping model in the same framework as the band transport model. The hopping model is then modified to include an external electric field dependent time constant. This allows the development of an expression for the total electric space charge field for the condidtion of an externally applied alternating electric field. This expression is used in the electromagnetic coupled wave theory to predict the two wave mixing gain. Experimental and theoretical results are then compared. AC photoconductivity experimental results and theoretical predictions are also presented and compared.