Optical dispersion relations in amorphous semiconductors

We report generalized expressions for the optical constants of amorphous (a) semiconductors. The dielectric function spectrum ε₂({ω}) is assumed to yield a continuous absorption obeying the power law ({}{ω})^-2({}{ω}-Eg{)}²$ and have a steep high-energy end at the high-energy cutoff ${E}c$, where ${E}g$ is the optical energy gap. The corresponding ${{{ε}}}₁(ω) spectrum shows clear structures both at the{E}g$ and at the ${E}c$ edges. By introducing the damping effect into the model, the optical spectra become structureless which are typically observed in amorphous semiconductors. Analyses are presented on the optical dispersion relations of a-Si, a-Ge, and a-GaAs, and the results are in satisfactory agreement with experimental data over the entire range of photon energies (1.5--6.0 eV).