Absorption spectrum of doped highly mismatched alloys

Highly mismatched alloys are a class of semiconductor alloys with large electronegativity differences between the alloying elements. We predict that the absorption spectrum due to transitions between the split bands of a doped highly mismatched alloy with a conduction band anticrossing shows qualitative features revealing the fractional distribution of states in the split bands and providing valuable insight into their electronic structure. Our prediction is based on the analysis of the joint densities of states for both direct and indirect transitions between the split bands. In particular, we predict a peak near the absorption edge, which arises due to the suppression of direct transitions at large momenta. As a result of the suppression of direct transitions, indirect transitions dominate the spectrum away from the edge of absorption. We present analytic forms of the near-absorption-edge and large-energy behaviors of the spectra, comparing them with the asymptotic forms of absorption from a single deep impurity level.