Localization of band-edge states in periodic models ofa-Si

Abstract

We study the nature of electronic eigenstates at the band edges of two continuous-distorted-network models of amorphous silicon with cubic periodic boundaries. We use the Slater-Koster implementation of the tight-binding method to find the electronic structure, where the form of the Hamiltonian is identical to that of a Lifshitz Hamiltonian; the effects of disorder are included only in the off-diagonal elements. We find that states at all band edges exhibit some degree of localization. However, we observe no sharp separation between localized and extended states, as is to be expected in a finite-sized model. States at the bottom of the conduction band exhibit stronger localization behavior than those at the top of the valence band, contrary to the generally expected lack of sensitivity of conduction-band-edge states to disorder relative to those at the valence-band edge.