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. Theoxidized 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. Theas 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 thereduced 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.Dedicated to O. F. Schirmer on the occasion of his 60th birthday