P6 <sub>3</sub> /mmc-Ge and their Si–Ge alloys with a mouldable direct band gap
Qingyang Fan, Wenzhu Zhang, Yanxing Song, Wei Zhang, Sining Yun
Abstract
Abstract Physical properties, such as stability, electronic properties, hole effective mass, electron effective mass, mechanical properties, structural properties, and optical properties of P6 3 /mmc-Ge 6 and their Si 6- x Ge x ( x = 1, 2, 3, 4, 5) alloys are investigated using ab initio calculations based on density functional theory. The anisotropic mechanical properties of the Young’s modulus of Si 6- x Ge x alloys are all slightly superior than those of diamond-Si, while the Young’s modulus of Si 6- x Ge x alloys in the (001) plane are isotropic ( E max = E min ). With the increase in the number of germanium atoms, Si 5 Ge and Si 4 Ge 2 exhibit direct band gaps of 0.63 eV and 0.18 eV, respectively. All other Si 6- x Ge x ( x = 3, 4, 5) alloys and P6 3 /mmc-Ge 6 exhibit metallicity properties. In addition, the effective masses of electrons and heavy holes of Si 4 Ge 2 along the x and y directions become substantially smaller than those of Si 6 and Si 5 Ge.