Study on the effect of grain boundary on the mechanical properties of polysilicon by molecular dynamics simulation

Three-dimensional molecular dynamics simulations are conducted to investigate the effect of grain boundary on the mechanical properties of polycrystalline silicon. The load-displacement curves and nanohardness curves are obtained. The coordination analysis method is introduced to visualise the motion of the silicon atoms. The diagram about stress distribution is applied to analyse the mechanical behaviour of polysilicon under stress. The results show that when the moving direction of the indenter is almost the same as the grain boundary, grain boundaries become sliding source, which causes the suddenly unloading phenomenon. As a result, the nanohardness is continuously decreasing in the process of sliding. When the moving direction of the indenter is perpendicular to the grain boundary, the dislocations of the polysilicon are limited at grain boundaries, pile-up phenomenon occurs, which means the hardening mechanism is directly related to the nanoscale grain boundaries.