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GeSn alloys have been regarded as a potential lasing material for a complementary metal-oxide-semiconductor-compatible light source. Despite their remarkable progress, all GeSn lasers reported to date have large device footprints and active areas, which prevent the realization of densely integrated on-chip lasers operating at low power consumption. Here, we present a 1D photonic crystal nanobeam with a very small device footprint of 7 lm 2 and a compact active area of $1.2 lm 2 on a high-quality GeSn-on-insulator substrate. We also report that the improved directness in our strain-free nanobeam lasers leads to a lower threshold density and a higher operating temperature compared to the compressive strained counterparts. The threshold density of the strain-free nanobeam laser is $18.2 kW cm À2 at 4 K, which is significantly lower than that of the unreleased nanobeam laser ($38.4 kW cm À2 at 4 K). Lasing in the strain-free nanobeam device persists up to 90 K, whereas the unreleased nanobeam shows quenching of lasing at a temperature of 70 K. Our demonstration offers an avenue toward developing practical group-IV light sources with high-density integration and low power consumption.

A method to remove the misfit dislocations and reduce the threading dislocations density (TDD) in the germanium (Ge) epilayer growth on a silicon (Si) substrate is presented. The Ge epitaxial film is grown directly on the Si (001) donor wafer using a “three-step growth” approach in a reduced pressure chemical vapour deposition. The Ge epilayer is then bonded and transferred to another Si (001) handle wafer to form a germanium-on-insulator (GOI) substrate. The misfit dislocations, which are initially hidden along the Ge/Si interface, are now accessible from the top surface. These misfit dislocations are then removed by annealing the GOI substrate. After the annealing, the TDD of the Ge epilayer can be reduced by at least two orders of magnitude to <5 × 106 cm−2.