Performance investigation of optically pumped ridge waveguide GeSn lasers: role of GeSn buffer in mid-infrared Si photonics.

GeSn alloys are promising for Si-based mid-infrared (MIR) lasers owing to their direct bandgap. This study compares the performance of optically pumped ridge waveguide GeSn MIR lasers fabricated without (Device A: Si/Ge/GeSn ~10%) and with (Device B: Si/Ge/GeSn 5%/GeSn ~10.41%) a GeSn buffer. At 77 K, Device A exhibited a lower threshold (454.77 kW/cm2) and higher maximum operating temperature (110 K) than Device B (470.21 kW/cm2, 100 K). Overall, optical confinement, carrier transport, and thermal effects critically influence performance beyond defect reduction. This study provides design insights for GeSn lasers, facilitating the development of efficient, integrated Si-photonics MIR light sources.