Optical properties and electronic structure of amorphous Ge and Si

The analysis of the infrared absorption bands in amorphous Ge which correspond to transitions between the three branches of the valence band has shown that the valence band wave-functions are delocalized over distances of the order 102Å. This is in sharp contrast with the observed low electrical conductivity. Possible reasons for this discrepancy are discussed. A general formula for absorption in amorphous structures is discussed and applied to the analysis of the absorption edges in Ge and Si.