Effect of high-temperature annealing on the optical-absorption edge of hydrogenated amorphous silicon-carbon films

Abstract

The effect of annealing temperatures on the optical-absorption edge of hydrogenated amorphous silicon-carbon alloys (a-SiC:H), prepared by the decomposition of a silane-methane gas mixture highly diluted with hydrogen, has been studied. A comparison of the absorption spectra of a-SiC:H films, obtained by reflectance and transmittance measurements and by the constant-photocurrent method, is presented. The optical band gaps (${\mathit{E}}_{\mathit{g}}$) decrease and the widths of the band tails (${\mathit{E}}_{0}$) increase with increasing annealing temperature. The low-energy absorption lines, in the dependence of the absorption coefficient on the photon energy for various annealing temperatures and in the dependence of absorption coefficient on the temperature for different isophoton energies, converge to a point. The higher the hydrogen content in the films, the larger the effects of annealing on the disorder in the sample structure. These results have been explained by use of structural-disorder models.