Band structure of SiGe: Coherent-potential approximation

The band structure of SiGe has been calculated using the coherent-potential approximation in conjunction with a realistic but local pseudopotential model. The effects of alloy disorder manifest themselves in complex band energies, each with an imaginary part inversely proportional to the electron lifetime. Spectral functions and the alloy denisty of states are also computed. The damping proves to be small, though it is not always given accurately by low-order-perturbation theory about the virtual crystal. Moreover, within the present local pseudopotential approximation, it affects only s electrons capable of penetrating the ionic cores, since outside the core region the alloy pseudopotential is like that of either limiting pure crystal. The effect of the damping on experimental quantities such as the optical absorption and electrical resistivity is very small.