Mechanical and electronic properties of SiGe alloy in Cmmm structure

• SiGe in Cmmm space group is proposed.
• The mechanical and electronic properties for Cmmm SiGe are calculated.
• Shear modulus, bulk modulus and velocity anisotropies are obtained.

Using the density functional theory, a first-principles calculation for a novel orthorhombic structure (z-phase) property of silicon, germanium and their alloy Si0.5Ge0.5 is carried out in this work. The crystal structure is optimized to be in agreement with existing results, and based on this, the elastic properties including elastic constants and moduli are calculated, satisfying the elastic stability criteria. The anisotropic properties are represented by multiple anisotropic factors and linear bulk moduli, and the results indicate z-phase Si0.5Ge0.5 performs slight anisotropy in the c-axis direction. Besides, solid sound velocities in different propagation orientations and modes as well as Debye temperature are predicted using elastic moduli. At last, the band structure and density of states of z-phase Si0.5Ge0.5 are calculated, and comes out z-phase Si0.5Ge0.5 is indirect band semiconductor with a narrow band gap.