Direct bandgap GeSn nanowires enabled with ultrahigh tension from harnessing intrinsic compressive strain

GeSn alloys are a promising emerging complementary metal–oxide–semiconductor compatible technology for applications in photonics and electronics. However, the unavoidable intrinsic compressive strain introduced during epitaxial growth has prevented researchers from pushing the performance of GeSn devices to the limit and realizing real-world applications. In this paper, we present a straightforward geometric strain-inversion technique that harnesses the harmful compressive strain to achieve beneficial tensile strain in GeSn nanowires, drastically increasing the directness of the band structure. We achieve 2.67% uniaxial tensile strain in 120 nm wide nanowires, surpassing other values reported thus far. Unique pseudo-superlattices comprising of indirect and direct bandgap GeSn are demonstrated in a single material only by applying a periodic tensile strain. Improved directness in tensile-strained GeSn significantly enhances the photoluminescence by a factor of 2.5. This work represents a way to develop scalable band-engineered GeSn nanowire devices with lithographic design flexibility. This technique can be potentially applied to any layer with an intrinsic compressive strain, creating opportunities for unique tensile strained materials with diverse electronic and photonic applications.