Three-element stressed Ge:Ga photoconductor array for the infrared telescope in space

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Abstract
A stressed Ge:Ga photoconductor array with three elements applied to the Infrared Telescope in Space satellite was fabricated and tested in experiments at 2.0 K in very low-photon-influx conditions (~105 photons/s). Stress was applied to three Ge:Ga detectors in a series by a stable and compact stressing apparatus by using cone-disk springs. The cutoff wavelength was ~180 μm. Responsivity was ~100 A/W, and the product of quantum efficiency and photoconductive gain, ηG, was ~1 with a chopping frequency of 2 Hz. The noise equivalent power was −18 W/Hz1/2 when low-noise transimpedance amplifiers were used. A slow transient response and a nonlinear response that was dependent on the background photon influx were observed in the experiments. The latter showed that the ηG had a time constant τc that was proportional to Nph−1/2.