Light-induced charge transport processes in photorefractive barium titanate doped with rhodium and iron

Absorption, light-induced absorption changes, photo and dark conductivities, bulk photovoltaic currents and two-beam coupling gain coefficients are measured for oxidized, as grown and reduced BaTiO3:Rh,Fe crystals. The oxidized sample shows hole conductivity and three photorefractive levels are present: Rh-4+/5+, Fe-4+/5+ and Rh-3+/4+. The measurements indicate that Rh-3+/4+ is responsible for the photo conductivity and that its energy level is located (0.9 +/- 0.1) eV above the valence band edge. The ns grown sample also shows hole conductivity and two photorefractive levels are involved: Rh-3+/4+ and Fe-3+/4+. The results yield that the Fe-3+/4+ level is located (0.95 +/- 0.05) eV above the valence band edge. In the reduced sample electrons are the dominant charge carriers and two levels are of importance. The shallow one is located (0.39 +/- 0.05) eV below the conduction band edge. Here the performance of this crystal is strongly impaired by a pronounced sublinear photo conductivity.