On the topological and electronic structure of amorphous semiconductors

Abstract

Using a basis of bonding orbitals and tight-binding matrix elements depending on the local topology the author has calculated the valence band densities of states (VBDOS) appropriate to a series of seven continuous random network (CRN) models of the structure of a-Si. Comparison with experimental data allows quantitative bounds to be put on the average number of 'wrong bonds' present in a-Si. A surprisingly large number of 'wrong bonds' are required before significant deviations from the form of the VBDOS of a purely even-ringed CRN are obtained. It is argued that in studies of the topological disorder of other such systems only two or three models of very different topologies need be considered in order to identify a typical topological structure.