In situ observations of crystal growth of spherical Si single crystals

Spherical Si single crystals for solar cell substrates have been grown successfully with a yield of almost 100%. Spherical Si multicrystals with diameters of approximately 400 μm in a teardrop shape were initially fabricated by a dropping method. The as-dropped spherical Si multicrystals were melted into droplets on a silica plate in an oxygen atmosphere, and the Si droplets were then recrystallized to form single crystals by supercooling within a specific temperature range. It was found that the recrystallization process occurred unidirectionally in each Si droplet, and recrystallized spherical Si single crystals free of defects (dislocations and oxidation-induced stacking faults, OSF) were obtained at a supercooling in the range of 12-42 °C. For supercooling ranging from 42 to 87 °C, spherical Si single crystals could still be obtained; however, many defects such as dislocations and OSF were generated. When the supercooling was larger than 87 °C, the crystal growth showed a dendritic growth mode and only multicrystals were obtained.