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 Ge_1-xSn_x alloys. The electronic band structure for biaxially-stressed Ge_1-xSn_x alloys is calculated using deformation potential theory and k·p method. For unstrained Ge_1-xSn_x 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 Γ- and L-valley conduction band edges, and hence quenching optical gain in Ge_1-xSn_x alloys.