Progress on Germanium-Tin Nanoscale Alloys

Group IV alloys have attracted interest in the drive to create Si compatible, direct band gap materials for implementation in complementary metal oxide semiconductor (CMOS) and beyond CMOS devices. The lack of a direct band gap in Si and Ge hinders their incorporation into optoelectronic and photonic devices, without the induction of undesirable strain. Alloying of Ge with Sn represents a novel solution to the lack of light emission in group IV compounds, with an indirect-to-direct band gap transition predicted for Ge at a Sn incorporation greater than 6.5 atom %. Recently, the initiatives on the GeSn alloy research have turned its focus to nanoforms to keep on track with the miniaturization of Si-related platforms for application in nano/optoelectronics, photonics, and energy devices. Here, we review recent advances in the growth and application of Ge nanomaterials. An overview of the theoretical band structure calculations for Ge and the effect of band mixing is briefly explored to highlight the significance of Sn inclusion in Ge for band gap engineering. Different fabrication methods for growing Ge alloy nanostructures are delineated and correlated with thin film growth. This highlights the requirement of low-temperature and kinetically driven nonequilibrium processes for growing these metastable nanoscale alloys. The optical and electrical properties for both Gestrain-relaxed one-dimensional (1D) nanostructures and nanopartides are reported as well as recent key research findings on Ge thin films, highlighting the potential application of these materials in photonic, nanoelectronic, and optotelectronic devices.