Molecular dynamics simulation of the solidification process of multicrystalline silicon from homogeneous nucleation to grain coarsening

Abstract

Based on the Stillinger–Weber potential, molecular dynamics simulations of the solidification processes of multicrystalline silicon were carried out. Every stage of the whole solidification process, including homogeneous nucleation, grain growth, grain coarsening and defect characterization, was investigated. In the nucleation stage, it showed two typical nucleation models (spontaneous nucleation and sporadic nucleation) at high and low temperatures. Local heterogeneity was occasionally observed during homogeneous nucleation. The simulated nucleation rates at different temperatures were measured, whose trends were in agreement with the results of theoretical calculations, and both of them reached the maximum nucleation rate at a critical temperature of ∼0.65T_m. In the growth stage, the nuclei showed the maximum growth exponent at ∼0.65T_m. The evolution of the grain number at different temperatures exhibited three different patterns. Furthermore, the grains showed modest anisotropic growth before the growth was influenced by other grains. In the grain coarsening stage, the grain size distribution could be described suitably by the log-normal distribution. The grain coarsening exponent was approximately one order of magnitude lower than the nuclei growth exponent. The analyses of crystal defects showed that the dislocation density is about 10⁵ m⁻², twin percentages are above 40%, and the percentage of CSL grain boundaries is about 30.30% in mc-Si of the simulations. The statistics of crystal defects are similar to experimental results.