Abstract

Bismuth silicon oxide (Bi₁₂SiO₂₀; BSO) is a wide band gap relaxation semiconductor with unique photorefractive and electrorefractive properties. Single-crystal BSO has been utilized in numerous optical processing and computing devices, including the Pockels readout optical modulator (PROM), the photorefractive incoherent-to-coherent optical converter (PICOC), and volume holographic optical elements (VHOEs). We report the characterization of device-relevant materials parameters induced by the Czochralski growth of nonstoichiometric bismuth silicon oxide (Bi_xSiO_1.5x+2). Several series of three compositionally altered crystals have been grown from the same starting melt of 6–9s purity. Melt compositions varied from x ≃ 13 to x ≃ 11.5, producing bismuth-rich, nearly stoichiometric, and silicon-rich crystals. The composition of the melt was adjusted after each growth run to compensate for the extracted weight and shift to the next melt composition as derived from the phase diagram.¹ By utilizing this method the influence of background impurities is minimized. A maximum of the dark volume resistivity (~3 × 10¹⁶ Ω cm) and photoconductivity occurs for the third crystal of each nonstoichiometric series (grown from a melt composition with x < 12). Within each series these crystals also exhibit the lowest value of optical absorption throughout the visible spectrum. Each series of crystals was characterized by a combination of optical and electrooptic methods including absorption spectroscopy, the electrooptic measurement of the volume resistivity² and photoconductivity, and the photorefractive grating recording applied to measurement of the effective trap density, holographic grating writing energy, and saturation diffraction efficiency.

© 1988 Optical Society of America