Optical absorption in amorphous semiconductors

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Abstract
We use the joint density-of-states function to study the optical-absorption spectrum of amorphous semiconductors. To determine the overall joint density of states, we average a local joint density of states over spatially correlated Gaussian distributions of conduction-band and valence-band potential fluctuations. Our results span the transition from below to above the energy gap and both analytical and numerical results are obtained. Spatial correlations are found to play a dramatic role in influencing the shape of the optical-absorption spectrum. We apply this formalism to the case of hydrogenated amorphous silicon and several other amorphous semiconductors of interest, and find that our results are consistent with those of experiment.