Hydrogen states in amorphous Ge

The removal of dangling bond states from the energy gaps of tetrahedrally bonded amorphous semiconductor is not the only effect when hydrogen is introduced. In addition to the bonding states deep in the valence band, we found that there are anti-bonding states appearing in the conduction band and near the bottom of the conduction band and, in some cases, even in the gap, as first conjectured by Paul et al. These latter states affect transport properties significantly as observed in photoconductivity.