Energy band model of undoped a-Ge : H prepared by plasma CVD

The infrared absorption, electronic properties including dark- and photoconductivities and optical properties of hydrogenated amorphous Ge thin films prepared by rf plasma CVD method at a substrate temperature of 130°C have been studied. It is found that hydrogens bond to Ge in a monohydride manner. An energy band model is proposed through the experimental results; the energy band gap is 1.0 eV, the Fermi level lies 0.35 eV below the conduction band, the electron trap level corresponding to the band tail edge is located 0.15 eV below the conduction band, and the hole trap level to the tail edge on the valence band side is situated 0.20 eV above the valence band.