Electronic Properties of Complex Crystalline and Amorphous Phases of Ge and Si. I. Density of States and Band Structures

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.