Optical and structural properties of Si _xSn _yGe _1-x-y alloys

A range of device quality Si _xSn _yGe _1-x-y alloys with unprecedented Sn content were grown and characterized. Spectroscopic ellipsometry analysis of these materials yielded dielectric functions as expected for a crystalline alloy with cubic symmetry. Incorporation of Si into SnGe yielded an additional reduction of the E ₂ critical point, as expected based on the E ₂ values of Si and Ge. The structure-composition relationship observed agrees well with first principles simulations and exhibits small deviations from Vegard's law behavior.