Theoretical Analysis of Strain Effect on Optical Gain in Ge1-xSnx Alloys

We present a theoretical analysis of strain effect on optical gain in biaxially-stressed Ge1-xSnx alloys. The electronic band structure for biaxially-stressed Ge1-xSnx alloys is calculated using deformation potential theory and k.p method. For unstrained Ge1-xSnx alloys, a Sn content of 6.7% is required to achieve a direct bandgap for providing optical gain. The introduction of tensile strain can further soften the requirements for indirect-to-direct bandgap transition, thereby enhancing optical gain. On the other hand, compressive strain significantly increases the energy difference between the Gamma- and L-valley conduction band edges, and hence quenching optical gain in Ge1-xSnx alloys.