Epitaxial Ge0.81Sn0.19 Nanowires for Nanoscale Mid-Infrared Emitters

Highly oriented Ge 0.81 Sn 0.19 nanowires have been synthesized by a low-temperature chemical vapor deposition growth technique. The nanostructures form by a self-seeded vapor–liquid–solid mechanism. In this process, liquid metallic Sn seeds enable the anisotropic crystal growth and act as a sole source of Sn for the formation of the metastable Ge 1– x Sn x semiconductor material. The strain relaxation for a lattice mismatch of ε = 2.94% between the Ge (111) substrate and the constant Ge 0.81 Sn 0.19 composition of nanowires is confined to a transition zone of <100 nm. In contrast, Ge 1– x Sn x structures with diameters in the micrometer range show a 5-fold longer compositional gradient very similar to epitaxial thin-film growth. Effects of the Sn growth promoters’ dimensions on the morphological and compositional evolution of Ge 1– x Sn x are described. The temperature- and laser power-dependent photoluminescence analyses verify the formation of a direct band gap material with emission in the mid-infrared region and values expected for unstrained Ge 0.81 Sn 0.19 ( e . g ., band gap of 0.3 eV at room temperature). These materials hold promise in applications such as thermal imaging and photodetection as well as building blocks for group IV-based mid- to near-IR photonics.