Optical critical points of SixGe1-x-ySnyalloys with high Si content

We extend the analysis of optical transition energies above 1.5 eV in ternary SixGe1-x-ySnyalloys grown by molecular beam epitaxy to a composition range in which 1-x-y is as low as 0.405. Simple models for transition energies assume a quadratic dependence on material content. Comparing our results to existing predictions of the transition energies based on results obtained from samples with much lower Si and Sn content, however, we find a significant disagreement between experiment and theory, indicating that the assumption of a quadratic dependence might not be valid for the entire composition range of the ternary alloy.