Theory of photorefractive effect for double carriers with two deep traps and a shallow hole trap

We propose a new theoretical model of photorefractivity which consists of both electron and hole carriers with two deep traps and a shallow hole trap. The model predicts that, if the shallow trap accumulates a large density of charge carriers, the photoconductivity will be a sublinear (or superlinear)function of light intensity, and the space-charge field will increase (or decrease) to a saturated value as the light intensity increases, depending on the sign of the dominant carrier. The comparison of this model with previous ones shows that it provides a more common description about the dependences of photoconductivity and space-charge field on the light intensity.