Ge:Be far infrared photoconductors

Germanium:Beryllium photoconductors have been optimized for the 30 to 50 micron m wavelength range. Crystal growth of detector quality material requires good control of both the Be and residual impurity doping. Detective quantum efficiencies of eta(sub d) = 46% at 5 A/W have been achieved at a photon background of 10 to the 8th power p/s. The responsivity of Ge:Be detectors can be strongly temperature-dependent when the residual shallow levels in the material are closely compensated. Transient responses on the order of approx. 1 second have been observed in some materials. The role of residual shallow impurities on the performance of photoconductors doped with semi-deep and deep impurities is discussed.