Theoretical Investigations of Si-Ge Alloys in P4₂/ncm Phase: First-Principles Calculations.

The structural, mechanical, anisotropic, electronic and thermal properties of Si, SiGe, SiGe and Ge in 4₂/ phase are investigated in this work. The calculations have been performed with an ultra-soft pseudopotential by using the generalized gradient approximation and local density approximation in the framework of density functional theory. The achieved results for the lattice constants and band gaps of 4₂/-Si and 4₂/-Ge in this research have good accordance with other results. The calculated elastic constants and elastic moduli of the Si, SiGe, SiGe and Ge in 4₂/ phase are better than that of the Si, SiGe, SiGe and Ge in 4₂/ phase. The Si, SiGe, SiGe and Ge in 4₂/ phase exhibit varying degrees of mechanical anisotropic properties in Poisson's ratio, shear modulus, Young's modulus, and universal anisotropic index. The band structures of the Si, SiGe, SiGe and Ge in 4₂/ phase show that they are all indirect band gap semiconductors with band gap of 1.46 eV, 1.25 eV, 1.36 eV and 1.00 eV, respectively. In addition, we also found that the minimum thermal conductivity of the Si, SiGe, SiGe and Ge in 4₂/ phase exhibit different degrees of anisotropic properties in (001), (010), (100) and (01¯0) planes.