The Influence of Cobalt Doping on Deep and Shallow Trap Dependent Photorefractive Properties of Barium Titanate

The photorefractive properties of cobalt­doping barium titanate have been recently reported by Rytz et al. [1]. High beam coupling gains were reported therein. Similarly, we have grown a series of cobalt-doped p-type barium titanate crystals, (undoped, 17 ppm, 50 ppm and 75 ppm), that also have relatively large beam coupling gains, e.g. for E||a and kg||c the gain is 7.4 cm−1 at 514.5 nm in the 75 ppm sample. We have further characterized these crystals by determining the sublinear dependence of the response time on intensity, the asymmetry of the beam coupling gain for ±C-axis crystal orientations, (i.e. electrooptic and absorptive coupling), intensity dependence of the gain, and light-induced dark decays. Experimental results indicate that, as the cobalt concentration is increased, the photorefractive character of the crystals change from "type B" to "type A" as defined by Mahgerefteh and Feinberg [2]. Type A crystals have filled hole-shallow traps and type B crystals have partially filled hole-shallow traps and thus low and high dark conductivity respectively.