We present calculations of the band structures and densities of states of Ge and Si in the diamond, wurzite, Si-III (BC-8), and Ge-III (ST-12) structures using the empirical-pseudopotential method and the tight-binding model used recently by Weaire. The increasing complexity of the crystal structures indicates that short-range disorder is able to account well for the density of states and optical properties of amorphous Ge and Si. This calculation also provides a method for explaining various features in the amorphous density of states and shows what structural aspects of the amorphous state are responsible for these features.

• Received 15 September 1972

DOI:https://doi.org/10.1103/PhysRevB.7.2644