(Invited) Tensile Strain Engineering and Defects Management in GeSn Laser Cavities

Abstract

We present GeSn material engineering to address both defect managements and band structure via tensile strain in laser cavities. We show that GeSnOI technologies allow to address both issues, with drastic reduction of power density thresholds in lasing devices at 2-3 µm wavelengths range.First set of analysis were performed on GeSn micro-disks with removed defects from their active region. The GeSn layers, grown on Ge strain-relaxed-buffers (SRBs) on silicon, were etched into micro-disks cavities. A specific chemistry were used to remove the dense misfit dislocation array from the suspended area of the GeSn disk, which constitutes the laser gain media. We obtained reduced lasing thresholds from hundreds of kW/cm2, as commonly obtained in the literature at low temperature, to around 10 kW/cm2 in pulsed regime with Sn content as low as 7 % to 10.5 %.In a second set of analysis we demonstrate a new approach relied on GeSn layers transfer on insulator, GeSnOI, with the aim to introduce SiNx stressor layers in an all-around geometry. [1,2] Tensile strain transfer from the stressor layers to GeSn micro-disks of 1.6% were reached, homogenously distributed in the disks volume. The defective interface were removed from the GeSn layer once it has been transferred on the host Si-substrate. This approach was applied to a GeSn layer with only 5.4% of Sn-content, which is nominally an indirect band gap semiconductor that cannot support lasing. The applied tensile strain transformed the Ge0.95Sn0.05 alloy into a direct-band gap material which support lasing with dramatically reduced thresholds, to 0.8 kW/cm2 at low temperature [3]. Tensile strain indeed yields to reduction of the valence band density of state by lifting the HH-LH degeneracy at the Γ-point, and thus contributes to reduce the lasing thresholds. The tensile strained GeSn lasers operate under continuous-wave-pumping up to 70 K thanks to further thermal management of the GeSnOI devices [3]. These results show the potential of new GeSn material engineering for future integration of laser sources on silicon platform using fully CMOS-compatible technology.[1] M. El Kurdi, M. Prost, A. Ghrib, et.al. ACS Photonics 3, 443 (2016).[2] A. Ghrib, M. El Kurdi, M. Prost, et. al. Adv. Opt. Mater. 3, 353 (2015).[3] A. Elbaz et. al. Nature Photonics, March (2020) doi.org/10.1038/s41566-020-0601-5