Ge : Ga photoconductors in low infrared backgrounds

Abstract

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.