Absorption and Transport Study of the Pseudogap in Amorphous Ge

Absorptance and spectral response of the photoconductivity data indicate the absorption edge in a-Ge is near hν=0.6 eV and not at 1 eV as suggested by other studies. The position of the optical threshold is obtained from in situ measurements on ultrahigh-vacuum---deposited films and is within experimental error of the thermal activation energy determined as the sum of the separation of the Fermi energy from the valence band and the high-temperature activation energy of the dc conductivity.