Ab initio simulation on ideal shear strength of silicon

Silicon single crystal is commonly used for electronic devices. Because an integrated circuit consists of various micro-materials, their deformation mismatch brings about stress concentration in the substrate. A defect such as dislocation induced by the stress concentration aggravates the subtle electronic property of silicon. As the substrate possesses high purity with no initial dislocation, the ideal strength under the resolved shear stress might be an important measure to predict dislocation nucleation. In this study, in order to evaluate precisely the critical shear strength, a numerical ab initio simulation is conducted on the silicon single crystal (slip plane: (1 1 1), slip direction: [1̄ 0 1]). Especially, the focus is put on the effects of normal stress and the inner displacement of atoms in the cell under the shear strain. The normal stress strongly affects on the instability strain, and the inner displacement remarkably decreases the strength. The peak stress of silicon crystal is about 10 GPa at the shear strain of 0.3. The band gap becomes narrow as the strain increases. Since it disappears at the shear strain of 0.2, the deterioration of electronic property is more sensitive to the shear deformation than the mechanical one.