Optically pumped low-threshold microdisk lasers on a GeSn-on-insulator substrate with reduced defect density

Despite the recent success of GeSn infrared lasers, the high lasing threshold currently limits their integration into practical applications. While structural defects in epitaxial GeSn layers have been identified as one of the major bottlenecks towards low-threshold GeSn lasers, the effect of defects on the lasing threshold has not been well studied yet. Herein, we experimentally demonstrate that the reduced defect density in a GeSn-on-insulator substrate improves the lasing threshold significantly. We first present a method of obtaining high-quality GeSn-on-insulator layers using low-temperature direct bonding and chemical–mechanical polishing. Low-temperature photoluminescence measurements reveal that the reduced defect density in GeSn-on-insulator leads to enhanced spontaneous emission and a reduced lasing threshold by ∼ 10 times and ∼ 6 times, respectively. Our result presents a new path towards pushing the performance of GeSn lasers to the limit.