Electrooptic measurement of the volume resistivity of bismuth silicon oxide (Bi 12SiO 20)

Abstract

Single crystals of bismuth silicon oxide (Bi 12SiO 20) and its isomorphs (including, for example, bismuth germanium oxide (Bi 12GeO 20)) have been utilized in a wide range of active electrooptic and acoustoopic devices, including the Pockels Readout Optical Modulator (PROM), the PRIZ, the Photorefractive Incoherent-to-Coherent Optical Converter (PICOC), volume holographic storage devices, and surface acoustic wave devices. A key material parameter that influences device performance characteristics is the volume resistivity, which is difficult to measure accurately using standard techniques in refractory oxides like Bi 12SiO 20 due to its large magnitude (typically 10 13ω cm). We present here a technique for the measurement of such very high resistivities in electrooptic materials; this method utilizes the electrooptic modulation induced by a voltage placed across the (crystallographically oriented) sample as a probe of temporal voltage transients that are in turn directly related to the sample volume resistivity. In our experiments, a very weak optical probe is frequency modulated, phase detected, and employed at low duty cycle to avoid ambiguities due to photoconductive voltage decay. The technique is described in detail, and experimental results are presented on a number of undoped and doped samples of bismuth silicon oxide grown by the Czochralski technique.