Growth and holographic characterization of nonstoichiometric sillenite-type crystals

We have grown Bi12GeO20 and Bi12SiO20 single crystals from melts with diffe rent GeO2 and SiO2 contents, respectively, to investigate the influence of an intrinsic defect, the antisite defect (Bi on Ge or Si site), on the ligh t-induced charge transport. The optical absorption and the effective trap d ensity of the crystals increase with decreasing GeO2 and SiO2 content in th e melt. Furthermore, a variation of the photoconductivity is observed. Our results can be described by a one-center model with the antisite defect Bi3 +/4+ on Ge or Si site as dominant photorefractive center. (C) 2001 American Institute of Physics.