Influence of disorder on the electronic structure of amorphous silicon

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Abstract
We have examined the electronic structure of amorphous silicon using a tight-binding scheme with all first- and second-neighbor couplings in a continuous random network. Matrix elements and deformation potentials were taken from the crystalline band structure. The effect of bond-length and bond-angle variations is relatively small and contributes to the narrow tails at the band edges. The effect of dihedral-angle disorder was examined keeping only the nearest-neighbor interactions in the Hamiltonian. The dihedral-angle disorder was found to be important at the valence-band edge and responsible for the observed features near the top of the valence band. Topological disorder was found to have important consequences in the bulk of the bands as well as at the conduction-band edge. Apart from the effects of the bond-length and bond-angle disorder, the states at the band edges are confined within regions closely approaching the crystalline structure locally, where they have the same form as in the crystal, but do not extend through the entire structure.