Point Defect Interaction With Dislocation In Silicon Based On Molecular Dynamics Calculation

With the demand of the speed and power of Si based semiconductor devices, the technology of band tailoring via stress is becoming more and more important. When putting a layer of Si buffer grown in low temperature between the SiGe epi-layer and Si substrate, there are large amount and kinds of defects in the buffer layer that alter the strain relaxation mechanism and make the final threading dislocation density very low. This method is studied widely and improved constantly in these 10 years, and the quality of Si_1-xGe_x layer is improved constantly. But the relaxation mechanism of this method is still under debate.Because the relief of lattice misfit stress is mainly depending on the glide of 60o dislocation on the {111} plane, a 60°dislocation dipole model was built by molecular dynamics simulation method based on the Stillinger-Weber potential and periodic boundary condition, point defect interaction with dislocation was investigated concretely.Firstly, a relatively simple method was presented to generate a dislocation dipole: divide the mixed dislocation into the edge and screw components, impose a displacement field to all atoms to establish the initial configuration, and then conduct a simulated annealing process for relaxation. Calculated formation energies of vacancies and self-interstitials near the core of a 60°dislocation are considerably lower than in the bulk.Secondly, the dislocation motion characteristics under lattice misfit stress are studied with Molecular Dynamics, the shear stress is applied with Parrinello-Rahman method. The velocity of dislocation interaction with vacancies and self-interstitials is slower than that of perfect dislocation, the velocity of dislocation increases as the stress increases, decreases as the temperature increases, which is consistent with the phonon drag model. It is more obvious that the phonon drag mechanism enhances during the motion of dislocation interaction with defects. The peierls stress decreases as the temperature increases, which is consistent with the Peierls–Nabarro model, and the peierls stress of dislocation interaction with defects increases largely. It can be concluded that the defects in the low temperature Si buffer will block the motion of misfit dislocation.