Direct bandgap GeSn microdisk lasers at 2.5 μm for monolithic integration on Si-platform

We report on the first experimental demonstration of direct bandgap group IV GeSn microdisk (MD) lasers (λem=2.5 μm) grown on Si(001). The evidence of lasing is supported by a detailed analysis of strain-dependent emission characteristics of GeSn alloys with xSn ≥ 12 at.%. Residual compressive strain within the layer is relieved via under-etching of the MD enabling increased energy offsets up to EL-EΓ=80 meV. The lasing threshold and max. temperature amount to 220 kW/cm2 and 135 K, respectively.