We report generalized expressions for the optical constants of amorphous (a) semiconductors. The dielectric function spectrum ${\mathrm{\epsilon }}_2$(ω) is assumed to yield a continuous absorption obeying the power law (ħω${)}^{\mathrm{-}2}$(ħω-${\mathit{E}}_{\mathit{g}}$${)}^2$ and have a steep high-energy end at the high-energy cutoff ${\mathit{E}}_{\mathit{c}}$, where ${\mathit{E}}_{\mathit{g}}$ is the optical energy gap. The corresponding ${\mathrm{\epsilon }}_1$(ω) spectrum shows clear structures both at the ${\mathit{E}}_{\mathit{g}}$ and at the ${\mathit{E}}_{\mathit{c}}$ 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).

• Received 13 November 1990

DOI:https://doi.org/10.1103/PhysRevB.43.12316