LIGHT-INDUCED CHARGE-TRANSPORT PROCESSES IN PHOTOREFRACTIVE BARIUM-TITANATE DOPED WITH RHODIUM AND IRON

Absorption, light-induced absorption changes, photo and dark conductiv ities, bulk photovoltaic currents and two-beam coupling gain coefficie nts are measured for oxidized, as grown and reduced BaTiO3:Rh,Fe cryst als. The oxidized sample shows hole conductivity and three photorefrac tive levels are present: Rh-4+/5+, Fe-4+/5+ and Rh-3+/4+. The measurem ents 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 valenc e band edge. The ns grown sample also shows hole conductivity and two photorefractive levels are involved: Rh-3+/4+ and Fe-3+/4+. The result s yield that the Fe-3+/4+ level is located (0.95 +/- 0.05) eV above th e valence band edge. In the reduced sample electrons are the dominant charge carriers and two levels are of importance. The shallow one is l ocated (0.39 +/- 0.05) eV below the conduction band edge. Here the per formance of this crystal is strongly impaired by a pronounced sublinea r photo conductivity.