Model dielectric function for amorphous semiconductors

We apply a model dielectric function, which was developed for modeling the optical spectra of crystalline semiconductors, to investigate the optical response in amorphous (a) semiconductors. By comparing the experimental valence- and conduction-band densities of states with the band theory, it is supported that the short-range order (chemical gap) is important to understand the ε(E) spectra both for crystalline and amorphous semiconductors. Analyses are presented for a-Si, and results are in satisfactory agreement with the experimental data over the entire range of photon energies.