Growth control and enrichment of Si crystals from Si-Sn melt by directional solidification

The growth control and enrichment of Si crystals using Si-50 at.% Sn melts via upwards and downwards directional solidification at various moving rates was investigated. As expected, a large area of quasi-bulk Si (98.6% enrichment percentage) was successfully obtained at the 0.01 mm/min upwards moving rate. Moreover, after HCl leaching, the residual at.% of Sn in the enriched Si area was easily reduced to the 0.00132-0.00163 range, which was almost the same as that for the solid solubility of Sn in Si. Furthermore, a model was established to explain the crystal growth process and enrichment mechanism during directional solidification. In conclusion, we chose the upwards moving direction for the follow-up experiments, which solved the most critical first step of using Si-based alloy solvent refining to produce solar grade Si.