(Digital Presentation) Gesnoi Laser Technology for Photonic-Integrated Circuits

Abstract

GeSn alloys have been regarded as a promising material for creating a complementary metal-oxide-semiconductor (CMOS)-compatible light source. Despite the remarkable progress in demonstrating GeSn lasers, an unavoidable intrinsic compressive strain introduced during epitaxial growth has prevented researchers from pushing the directness of GeSn gain media to the limit and realizing practical GeSn lasers. In this paper, we demonstrate a GeSn-based 1D photonic crystal nanobeam laser on a high-quality GeSn-on-insulator (GeSnOI) substrate which allows releasing the limiting compressive strain, thus improving the threshold and operating temperature. Pump-power-dependent photoluminescence measurements show a lasing threshold density of 18.2 kW cm−2 at 4 K for the released strain-free GeSn nanobeam, which is ~2 times lower than that of the unreleased GeSn nanobeam with compressive strain. The improved bandgap directness in the released GeSn nanobeam also allows achieving lasing action at higher operating temperatures up to 90 K compared to the unreleased laser device (<70 K). We also report a straightforward geometric strain-inversion technique that harnesses the harmful compressive strain to achieve ultrahigh tensile strain in GeSnOI nanowire, drastically improving the directness of the bandstructure. We achieve ~2.67% uniaxial tensile strain in ~120 nm wide nanowires, surpassing other values reported thus far. We also demonstrate unique superlattices comprising of indirect and direct bandgap GeSn are demonstrated in a single material only by applying a periodic tensile strain. Increased directness in tensile-strained GeSn significantly enhances the photoluminescence intensity by a factor of ~2.5. Our demonstration offers an avenue toward developing practical CMOS compatible light sources.