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 (0.25 T m , T m is the melting temperature, 1685 K for Si) has been reproducibly achieved in slowly cooled silicon droplets ( ∼ 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.