Amorphous bismuth-germanium thin films: Infrared detector characterization

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 -Bix Ge1−x thin films possess moderate potential as a new amorphous infrared detector material. The Bix 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.