Comparison of single- and two-species models of electron–hole transport in photorefractive media

For most regimes descriptions of photorefractive behavior by electron–hole transport with a single species of impurity levels and by electron–hole transport with two species of impurity levels are significantly different. The steady-state space-charge field depends on the model used, and the presence of two response rates and complementary gratings requires the presence of two species. For appropriate grating spatial frequencies, electric fields, and time limits, however, the models give similar results. We describe these regimes of difference and similarity.