Transport Processes of Photoinduced Carriers in Bismuth Germanium Oxide (Bi12GeO20)

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Abstract
This paper describes some investigations aimed at understanding the transport processes of excess carriers in bismuth germanium oxide (Bi12GeO20). Spectral photoconductive response, photoconductive decay, and optical absorption were measured. Photoconductivity exists over a relatively narrow wavelength range with a peak at 0.5 μ, which coincides with a peak in optical rotary power. Apparently the same set of transitions is involved in these effects. When the metallic‐end contacts of the sample are illuminated, additional photoconductivity appears at shorter wavelengths. Photoconductive decay times of 1.2×10−2, 6×10−4, and 1.9×10−4 sec have been observed; the first we attribute to free carriers and the remaining two to spacecharge effects. There are strong indications that only a very small portion of absorbed photons contributes to photoconductivity.