Simulation study of nucleation mechanism of grown-in dislocations near grain boundary during solidification of silicon

We carried out molecular dynamics (MD) simulations of directional solidification of silicon with carbon impurity to study the nucleation mechanism of grown-in dislocations near Σ27 grain boundary. We find that carbon impurity atoms segregate to crystal boundary groove. A stacking fault composed of two consecutive {111} bi-layer plane twinnings nucleates near the carbon segregation site in the grain boundary groove. Then Shockley partial dislocations composed of 5-5-8-atom rings are formed between stacking fault area and normal stacking area. These dislocations originate from the grain boundary, pass through the crystal, extend to the solid-liquid interface and expand with the movement of the solid-liquid interface, indicating that they are grown-in dislocations formed during the directional solidification of silicon. Our study is expected to provide a theoretical basis for further reducing the dislocation density of multicrystalline silicon (mc-Si).