A hybrid functional first-principles study on the band structure of non-strained Ge_1-xSn_x alloys

Using hybrid-functional first-principles calculation combined with the supercell method and band unfolding technique we investigate the band structure of non-strained Ge_1-xSn_x alloys with various Sn concentrations. The calculations show that at the Sn concentration of~3.1 mol% the GeSn alloy presents a direct band gap. The variation of the band structure are ascribed to the weaker electro-negativity of Sn atoms and a slight charge transfer from Sn atoms to Ge atoms.