OPTICAL DISPERSION-RELATIONS IN AMORPHOUS-SEMICONDUCTORS

We report generalized expressions for the optical constants of amorphous (a) semiconductors. The dielectric function spectrum epsilon-2(omega) is assumed to yield a continuous absorption obeying the power law (h-omega)-2(h-omega-E(g))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 epsilon-1(omega) 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).