Transport properties of photoelectrons in Bi12SiO2

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Abstract
An optical method for studying the transport properties of photogenerated electrons in the photoconducting electro‐optic crystal of Bi12SiO20 is described. The physical model in which the free electrons are assumed to hop from the donor sites to the trapping sites and thus create a space‐charge field has been developed. The crystal is mounted in a transverse configuration with the light beam propagating along the [11̄0] axis and the electric field applied along the [110] axis. By measuring the photoinduced birefrigence variations, we determine the quantum efficiency φ of generating a free electron by an absorbed photon, the range μτ of a photoelectron, and the dark conductivity of the material. φ varies from 1.00 to 0.03 when the incident wavelength changes from 400 to 700 nm. The range μτ is found to be 5.2×10−6 cm2/V and the dark conductivity 2×10−15 (Ω cm)−1.