High undercooling of bulk molten silicon by containerless processing

When containerless electromagnetic levitation processing was applied to elemental semiconductor Si using a two-step heating method proposed by the present authors, a substantial degree of undercooling up to 420 K (0.25T(m), T-m is the melting temperature, 1885 K for Si) has been reproducibly achieved in slowly cooled silicon droplets (similar to 7.6 mm in diameter). The microstructural change from faceted twins grown at low or intermediate undercoolings to twin-free grains formed at high undercoolings indicates a transition of solidification mechanisms. The experimental results, of which both the undercooling level and the sample volume surpass the previous work, lead to a reassessment of the nucleation frequency and the crystal/melt interfacial energy of undercooled Si liquid.