Tuning indirect-to-direct bandgap of lonsdaleite Si0.5Ge0.5 alloy via compressive strain for optical gain

This work presents theoretical insights on the electronic bandstructure and optical absorption of lonsdaleite Si0.5Ge0.5 alloy under uniaxial compressive strain. Within the framework of density functional theory (DFT), the electronic and absorption characteristics were calculated by modified Becke-Johnson (mBJ) potential with consideration of spin-orbit coupling (SOC). An indirect-to-direct transition of band gap along with a boost in absorption coefficient is observed in strained alloys, which can be promising for SWIR and mid-IR photonic applications. Optical gain was calculated to demonstrate the applicability of such materials in photonic devices.