Electronic Structure and Optical Properties of Amorphous Ge and Si

The amorphous density of states for an assembly of atoms with short-range order has been obtained from a phenomenological model in which the density of states of the corresponding crystal with different nearest-neighbor distances (±{} 5% of crystalline value, r₀) are averaged by introducing a suitable weighting function of the form exp[-(12σ²)(r₀-r)²], σ being the Gaussian spread. The pseudopotential formalism is employed in the calculation. The nondirect transition model of Tauc and energy-dependent matrix elements have been used to evaluate the imaginary part of the dielectric constant, ε₂(ω). The density of states and ε₂(ω) of amorphous Ge and Si are reported in this paper.