Explanation of the apparent sublinear photoconductivity of photorefractive barium titanate

Abstract

We explain the apparent sublinear intensity dependence of photoconductivity in barium titanate. In our model shallow acceptors act as a reservoir for charges optically excited from the donors. As this reservoir fills, the fraction of occupied donors changes appreciably, changing the lifetime of the free carriers. We identify two types of barium titanate crystals having quite different photorefractive characteristics, depending on their relative density of donors and acceptors, and we find that the depth of the shallow acceptor level is \ensuremath{\sim}0.4\ifmmode\pm\else\textpm\fi{}0.1 eV in both types of crystals.