Achieving direct band gap in germanium through integration of Sn alloying and external strain

GeSn is predicted to exhibit an indirect to direct band gap transition at alloy Sn composition of 6.5% and biaxial strain effects are investigated in order to further optimize GeSn band structure for optoelectronics and high speed electronic devices. A theoretical model has been developed based on the nonlocal empirical pseudopotential method to determine the electronic band structure of germanium tin (GeSn) alloys. Modifications to the virtual crystal potential accounting for disorder induced potential fluctuations are incorporated to reproduce the large direct band gap bowing observed in GeSn alloys.