The Band Structure of Si III and Ge III

Band structures have been calculated for the Si III and Ge III crystal structures, using a simple model Hamiltonian of tight binding type, with parameters appropriate to Ge. The calculations indicate, inter alia, that fivefold rings of bonds have important consequences for the band structure of a tetrahedrally bonded solid. Certain band edges are shifted if the structure contains many fivefold rings, as does Ge III. Current models for amorphous Si and Ge involve such rings, and it is suggested that if amorphous tetrahedrally bonded Sn could be made, the existence of a sufficient proportion of fivefold rings in the structure might result in this being a semiconductor with a sizeable gap (∼0.5 eV).