Abstract
The photorefractive effect is caused by a light-induced redistribution of charges among deep traps. This redistribution of charges creates a space charge field, which modulates the refractive index of the photorefractive material via the linear electrooptic effect, it is known that the simultaneous occurrence of holes and electrons in the involved charge transport process leads to a reduction in the strength of the resulting space charge field from that for electrons or holes alone. We extend the single-carrier band-conduction model of Kukhtarev2 by supposing that both electrons and holes can be excited from, and recombine with, the same species of traps. We find a grating wave vector dependence of the space charge field which is different from the single charge carrier case. When the hole-electron competition is nearly balanced, we predict that the space charge field changes its sign as a function of grating period. Such an anomalous behavior has been observed in beam coupling measurements in BaTiO3.3 Using our extended model we are able to fit the observed anomalous data within experimental error by adjusting four parameters: an effective trap density, the ratio of excitation rates of electrons and holes, and the mobility-lifetime products of each, see Fig. 1. We suggest further experiments to test the validity of our extended model.
© 1986 Optical Society of America
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