Electronic structure and optical properties of amorphous germanium and silicon

The complex band structures, the imaginary parts of the dielectric constant, and the densities of states of electrons in amorphous Ge and Si are calculated using a generalized pseudopotential formalism based on the Green's function techniques. The short range order is assumed to be the same as in the cubic crystalline systems. The long‐range order is relaxed by using a two particle correlation function, consisting of Gaussian functions centered at the lattice points. The half widths of the Gaussian functions increases with increasing lengths of the lattice vectors. It turns out, that the band edges near axis Γ‐L are less influenced by disorder than for other k ‐points in the Brillouin zone. This is confirmed by comparing the calculated imaginary part of the dielectric constant with the experimental one.