CALCULATION MODEL FOR THE OPTICAL-CONSTANTS OF AMORPHOUS-SEMICONDUCTORS

We present a phenomenological expression for the calculation of the optical constants, the refractive index, the extinction coefficient, and the absorption coefficient, of amorphous (a) semiconductors. Our proposed model requires four parameters, namely E(g) (optical energy gap), E(c) (high-energy cutoff), D (nondirect-transition strength), and GAMMA (damping). The damping parameter GAMMA is considered to reflect the distribution of electronic states rather than being the consequence of disorder broadening. Analyses are presented for a-Si, a-Ge, and a-GaAs, and results are in satisfactory agreement with the experimental data over the entire range of photon energy (1.5-6.0 eV).