Structural disorder and optical gap fluctuations in amorphous silicon

Optical absorption and Raman spectra in a number of a-Si, a-Si:H and a-(Si:H):B samples have been investigated. It is shown that the optical gap changes are weakly correlated with the changes in TO peak width in Raman spectra but are well correlated with the changes in the TA peak intensity. The correlation between the amplitude of optical gap fluctuations, determined from the optical absorption spectra, and the TA peak intensity has been observed. These results suggest that the optical gap and the amplitude of its fluctuations in amorphous silicon and its alloys depend not only on bond-angle dispersion but also substantially on the degree of structural disorder on a scale of about 4-6 AA or greater.