Infrared Absorption, Photoconductivity, and Impurity States in Germanium

Abstract

Infrared absorption and photoconductivity in $p$-type germanium with gold and copper impurities have been investigated at different temperatures. Photoconductivity in gold-doped germanium at liquid nitrogen and liquid helium temperatures shows a long wavelength tail beyond the fundamental absorption edge, which falls off sharply at about 6 microns corresponding to 0.21 ev. This value agrees well with the acceptor activation energy determined by electrical measurements. For copper-doped germanium at low temperatures both absorption and photoconductivity show a maximum at about 22 microns corresponding to 0.055 ev. This value also agrees with the acceptor activation energy given by Hall effect measurements. At room temperature more absorption is found in the region 2 to 5 microns as compared to $p$-type germanium doped with indium and aluminum. This is likely to be due to photoionization from a deeper level 0.25 ev above the valence band.