Thermal stress induced dislocation distribution in directional solidification of Si for PV application

This paper presents the limitation of the cast technique for silicon growth and the obstacle to reduce the dislocation density below 10³ cm^-2. The thermal stress induced dislocation density, independent of other dislocation sources, is determined and the result suggests that local dislocation densities as high as 10⁴ cm^-2 are readily introduced alone in the cooling period of the crystal growth. Areas of high residual strain and dislocation densities are identified and presented. The experimental results are correlated with numerical simulation based on a three-dimensional Haasen-Alexander-Sumino (HAS) model. The dislocation introduction is caused by an activation of different slip systems in different ingot areas.