Ge : Ga photoconductors in low infrared backgrounds

We report the development of infrared photoconductive detectors which are background fluctuation noise limited at photon fluxes ≲108 s−1. The detectors were fabricated from germanium doped with 2×1014 cm−3 gallium. Detectors operated in the conventional manner at T=3 K showed significant photoconductive response for wavelengths out to 120 μm with a minimum NEP of 2.4×10−17 W Hz−1/2 at 94 μm. Detectors operated at T=2 K with a uniaxial stress of 60 kgf mm−2 applied along a [100] direction showed significant response to 205 μm and gave a minimum NEP of 5.7×1017 W Hz−1/2 at ≈150 μm. The stressed detectors are four orders of magnitude more sensitive than any previous photoconductor beyond 120 μm.