Ultra-low-threshold continuous-wave and pulsed lasing in tensile-strained GeSn alloys

Description

Strained GeSn alloys are promising for realizing light emitters based entirely on group IV elements. Here, we report GeSn microdisk lasers encapsulated with a SiNx stressor layer to produce tensile strain. A 300nm GeSn layer with 5.4 at. % Sn, which is an indirect band-gap semiconductor as-grown, is transformed via tensile strain engineering into a direct band-gap semiconductor that supports lasing. In this approach the low Sn concentration enables improved defect engineering and the tensile strain delivers a low density of states at the valence band edge, which is the light hole band. We observe ultralow-threshold continuous wave (cw) and pulsed lasing at temperatures of up to 70K and 100K respectively. Lasers operating at a wavelength of 2.5 µm have thresholds of 0.8 kW cm −2 for ns-pulsed optical excitation, and 1.1 kW cm −2 under cw optical excitation. The results offer a path towards monolithically integrated group IV laser sources on a Si photonics platform.

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