Optical properties and size/shape dependence of α-Sn nanocrystals by tight binding

The semiconducting diamond structure of alpha-Sn may be stabilized by embedding nanocrystals in a suitable host. Based on a very accurate tight binding parametrization we calculate electronic and optical properties of round, as well as faceted nanocrystals, under both no, tensile and compressive strain. Nanocrystals with radii up to 2.6 nm are treated and are found to cover an energy range starting at near-zero band gap energy, with both size and also strain playing a significant role in determining the electronic properties. The HOMO-LUMO optical transition is found to be strong even for larger crystals, making them an attractive candidate in many potential NIR applications. Furthermore, exciton effects are estimated for bulk and nanocrystals and are found to be weak.