Electrical and Optical Properties of Amorphous Germanium

The temperature dependence of conductivity, optical absorption, photoconductivity spectra and the influence of annealing on these properties have been measured on amorphous Ge films of 0.49 to 3 µm thickness. The resistivity of films is 80∼130 Ω·cm and the sharp absorption edge occurs at ∼0.6 eV. The photoconductivity spectra have two peaks at photon energies of 0.8 and 1.0 eV. One peak at 1.0 eV is in excellent agreement with the mobility gap determined from high temperature conductivities. From the annealing experiments, the other peak at 0.8 eV has been ascribed to the peak density of the localized states near the valence band. An energy band model of amorphous Ge has been proposed for consistent explanations of experimental data.