Nanotechnology reviews: Direct bandgap transition for emission in GeSn nanowires

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Information:: Abstract: We investigate the structural, energetic, and electronic properties of Sn-doped germanium nanowires (NWs) along [001] direction, with various diameters. The direct bandgap transition is explored by the tensile strain of GeSn alloy for emission near 0.8 eV in the third optical communication window. Our first-principles calculations show that the direct bandgap transformation can be achieved in GeSn NW-shell with uniaxial strain change. Drawing inspiration from the significant expansion of Ge volume, the 7.5–14.04% Sn is proposed to be doped into the GeSn alloy for a dramatic transition into a direct bandgap in NWs. The calculation demonstrates that the direct bandgap transition is determined not only by the doping contents of Sn atoms, but also by changing symmetry and distribution region of the Sn atomic in GeSn alloy, where the Sn concentration is needed to transform into direct bandgap increases with the larger diameter of NWs. According to these results, a physical model with three levels system for stimulated emission in the optical communication windows is built, in which the external quantum efficiency of emission is higher than 20%.