Amorphous bismuth-germanium thin films: Infrared detector characterization

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Abstract
Thin films of bismuth‐germanium have been fabricated in vacuum by the method of codeposit vapor quenching. In this paper, the third of a three part series, the evaluation of a select set of amorphous bismuth‐germanium thin films as infrared detectors is reported. The evaluation indicates that a ‐Bi x Ge1−x thin films possess moderate potential as a new amorphousinfrared detector material. The Bi x Ge1−x system is found to be photoconductive in the range 0≤x≤0.037. Signal, noise, and signal‐to‐noise—ratio data at 300 and 162 °K are reported for various alloy concentrations. A clear maximum in the signal‐to‐noise plots is observed indicating an optimum bias regime. Photoresponse versus optical chopping frequency data indicate response times on the order of 1–2 msec at room temperature and at 162 °K. The specific spectral detectivity Dλ* for an a ‐Bi1.74Ge98.26 film at T = 162 °K shows a maximum in the vicinity of 1 μ with a maximum value in the range 107–108 cm Hz1/2 W−1.

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