Prediction of novel phase of silicon and Si–Ge alloys

Abstract

The structural, thermodynamic, elastic, anisotropic and electronic properties of P2221-Si have been studied using first-principles calculations. The elastic constants are satisfied with mechanical stability criteria. The mechanical anisotropy is predicted by anisotropic constants Poisson's ratio, shear modulus, Young's modulus and three dimensional curved surface of Young's modulus. These results show that P2221-Si and Si–Ge alloys are anisotropic. The sound velocities in different directions and Debye temperature for P2221-Si and Si–Ge alloys are also predicted. Electronic structure study shows that P2221-Si is an indirect semiconductor with band gap of 0.90eV. In addition, the band structures of Si–Ge alloys are investigated in this paper. Finally, we also calculate the thermodynamics properties and obtained the relationships between thermal parameters and temperature.