Lowering GeSn lasing thresholds for future integration on Si (Conference Presentation)

Lasing in bulk GeSn alloys have been reported lately with relatively high thresholds in the range of several hundreds of kW/cm². This can be mainly attributed to high defect densities of high Sn content alloy thick layers grown on relaxed Ge-VS. Indeed the use of high Sn contents in Ge(1-x)Snx alloy to reach direct band gap alignment (with xSn>10%) consequently results in large lattice mismatches with Ge and therefore produces large defect densities in partially relaxed thick layers. We show here that GeSn alloys with low Sn content exhibit strongly reduced lasing thresholds densities, in the 10 kW/cm² range, in microdisk cavities. We developed a layer transfer technology enabling management of the GeSn/Ge defect interface thus allowing to further reduce lasing thresholds in the kW/cm² range. The layer transfer additionally allows tensile strain engineering using silicon nitride stressor layer to increase the band structure directness as required for RT-laser operation.