Optical absorption, disorder, and hydrogen in amorphous silicon

We study how bonded hydrogen influences the optical absorption spectrum of amorphous silicon. We use a model for optical absorption in which the local form of the joint density of states is averaged over a Gaussian distribution of energy-gap fluctuations, this distribution being characterized by a mean energy gap and a standard deviation about this mean. We then fit this model to optical absorption data, and study how the modeling parameters vary with the bonded hydrogen concentration. We find that for the group of samples that we have considered, for bonded-hydrogen concentrations less than 10 at.%, we can adequately fit the data with a constant mean energy gap and a variable standard deviation that decreases with increasing bonded-hydrogen concentration. This suggests that bonded hydrogen plays a significant role in decreasing the amount of disorder in amorphous silicon.