Interface intermixing influence on the electronic and optical properties of Si/Ge strained-layer superlattices

The influence of interface intermixing on the electronic and optical properties of strain-symmetrized Si/Ge superlattices grown on a ${\mathrm{Si}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Ge}}_{\mathit{x}}$(001) alloy surface is studied. We find that interface intermixing plays an important role in the determination of the properties near the gap. In particular, it increases the fundamental gap of the superlattice and produces a variation of the absorption coefficient near the gap of the form α(E)∝(E-${\mathit{E}}_{\mathit{g}}$ ${)}^2$. A simple alloy layer model with approximately four intermixed Si-Ge atomic layers at the interface can account for the experimental observations.