Ideal amorphous semiconductors

We have examined the electronic structure of amorphous silicon (or germanium) in an ideal network structure using a tight-binding model with all first and second neighbor couplings. Matrix elements were taken from the crystalline band structure and deformation potentials. Quantitative disorder is relatively small. Topological disorder and the quantitative variations in dihedral angle give rise to limit-like behavior at the gap edges. The band tails are narrow and the minimum deep in such an ideal amorphous semiconductor.