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

Abstract

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 300 nm-thick GeSn layer with 5.4 at% Sn, which is an indirect-bandgap semiconductor as-grown, is transformed via tensile strain engineering into a direct-bandgap 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 ultra-low-threshold continuous-wave and pulsed lasing at temperatures up to 70 K and 100 K, respectively. Lasers operating at a wavelength of 2.5 μm have thresholds of 0.8 kW cm−2 for nanosecond pulsed optical excitation and 1.1 kW cm−2 under continuous-wave optical excitation. The results offer a path towards monolithically integrated group IV laser sources on a Si photonics platform.

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Fig. 1: Structural and optical characterization.
Fig. 2: Continuous-wave lasing from GeSn.
Fig. 3: Carrier density at threshold and net gain.
Fig. 4: Pulsed laser.

Data availability

The data that support the plots within this paper and other findings of this study are available from the corresponding authors upon reasonable request.

Code availability

Finite-element modelling was performed using commercially available COMSOL software. All other calculation codes were used in published works where model details are provided. The codes are not publicly available; any requests should be sent to the corresponding authors.

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Acknowledgements

M.E.K. and A.E. thank R. Colombelli and A. Bousseksou for discussions and their help with mounting the PL set-up with the FTIR spectrometer. We thank G. Mussler for XRD measurements. This work used knowledge acquired in the collaboration with H. Sigg from PSI. This work was supported by the French RENATECH network, the French National Research Agency (Agence Nationale de la Recherche, ANR) through funding of the ELEGANTE project (ANR-17-CE24-0015) and the Deutsche Forschungsgemeinschaft (DFG) via the project ‘SiGeSn Laser for Silicon Photonics’. A.E. was supported by ANRT through a CIFRE grant. A.F. acknowledges funding within the ANR-16-CE09-0029-03 TIPTOP project.

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All authors contributed to the work. P.B., M.E.K. and A.E. designed the device structure. M.E.K. and A.E. performed the strained disks fabrication with E.H., I.S., K.P. and G.P. M.E.K. and A.E. performed the PL measurements and laser experiments with N.Z. and X.C. K.P., G.P., I.S., N.v.d.D. and D.B. performed the structural analysis of the material. The GeSn layer was grown by D.B. and N.v.d.D. on substrates from J.-M.H. The Raman analyses were performed by A.F. and R.O. P.B., S.S. and Z.I. contributed to the modelling with M.E.K. and D.B. The work was supervised by D.G., F.B., P.B., D.B. and M.E.K. P.B., M.E.K., N.v.d.D., D.G. and D.B. wrote the manuscript.

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Correspondence to Dan Buca or Moustafa El Kurdi.

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Elbaz, A., Buca, D., von den Driesch, N. et al. Ultra-low-threshold continuous-wave and pulsed lasing in tensile-strained GeSn alloys. Nat. Photonics 14, 375–382 (2020). https://doi.org/10.1038/s41566-020-0601-5

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