On the average-gap model in amorphous materials

The dispersion of the subband refractive index in amorphous semiconductors is well described by "average gap" model which is based on two-band model of optical transitions. The disorder potentials due to the "electrostatic" and "elastic" forces determine the variation of the conduction-and valence-band edges. The average gap is defined as the difference between the most probable values of the bottom of the conduction band and the top of the valence band. The model is applied on a-Si/sub 1-x/C/sub x/:H, a-C:H and a-SiO/sub x/N/sub y/ layers.