ELECTRONIC-STRUCTURE AND LOCALIZED STATES IN A MODEL AMORPHOUS-SILICON

The electronic structure of a model amorphous silicon (a-Si) represent ed by a supercell of 4096 silicon atoms [B.R. Djordjevic, M.F. Thorpe, and F. Wooten, Phys. Rev. B 52, 5685 (1995)] and of a model hydrogena ted amorphous silicon (a-Si:H) that we have built from the a-Si model are calculated in the tight-binding approximation. The band edges near the gap are characterized by exponential tails of localized states in duced mainly by the variations in bond angles. The spatial localizatio n of the states is compared between a-Si and a-Si:H. Comparison with e xperiments suggests that the structural models give good descriptions of the amorphous materials.