Light-induced dark decay and sublinear intensity dependence of the response time in cobalt-doped barium titanate

Abstract

We report how the photorefractive properties of cobalt-doped barium titanate (BaTiO3) are influenced by deep and shallow traps. The light-induced dark decay of the space-charge field has two distinct time constants. The faster decay is due to the thermalization of charges from shallow traps, whereas the longer decay is that from deep traps formed when BaTiO3 is doped with cobalt. This dopant substantially decreases the dark conductivity of BaTiO3 and thus increases the dark storage time. The power coefficient of the sublinear intensity dependence of the photorefractive response time progressively increases with the cobalt-dopant concentration. Apparently cobalt doping of the deep level eliminates the effect from the shallow level in BaTiO3. Although cobalt-doped BaTiO3 has an increased effective trap density and thus an increased electrooptic gain, the response time and absorption are also increased, which thus decreases the photorefractive sensitivity.