Point defects in relaxed and strained Si studied by molecular dynamics method

Molecular dynamics simulations using the Tersoff potential have been performed to investigate the perturbation effects caused by different kinds of the point defects (vacancies and substitutional impurities) on the strained and relaxed Si matrices. Lattice distortion, mean square displacement, pair correlation function and vibrational spectra are studied. It is found that Ge substitution lead to little distortion of the Si matrix. However, vacancy and C substitution lead to more distortion. Diffusion directions of Si atoms around different kinds of point defects are different. When C substitution is introduced in the relaxed Si matrices or Ge substitution is introduced in the strained Si matrices, the system needs longer time to reach equilibrium. The crystallinity and symmetry degree of relaxed Si matrices are more satisfying than those of strained Si matrices after relaxation. Changes of the vibrational spectra caused by vacancy and C substitution are obvious. All above have a great effect on the photoelectric properties of the materials.