Monolithically Integrated Ultra‐Low Threshold GeSn‐on‐Insulator Laser Using Rapid Melting Growth

Abstract A low‐threshold, monolithically integrated laser on Si is considered a crucial missing ingredient in realizing efficient fully functional photonic‐integrated circuits (PICs). Owing to its compatibility with complementary metal‐semiconductor‐oxide (CMOS) processes, direct bandgap GeSn alloy has recently been studied intensively in hopes of making GeSn lasers the mainstream technology for PICs. However, the inevitable formation of harmful defects in GeSn directly grown on Si has thus far required the use of non‐monolithic approaches such as wafer bonding to obtain high‐quality GeSn layers, preventing the realization of practical, low‐threshold GeSn lasers. Here, ultra‐low threshold lasing in a monolithically‐grown, nearly‐defect‐free GeSn single‐crystal layer is demonstrated. The rapid melting growth method used in this study allows the fabrication of a compact, integrated laser that simultaneously achieves an ideal GeSn gain medium with built‐in tensile strain and an excellent GeSn optical cavity on an insulating layer. The measured threshold is ≈0.52 kW cm −2 under the optical pumping scheme at 10 K, which is the lowest among all the reported GeSn lasers. This work provides a new solution for building a truly CMOS‐compatible, monolithic laser that can complete the device library of the mature Si photonics foundries.