Morphological transformation of a crystal-melt interface during unidirectional growth of silicon

We investigated the morphological transformation at Si (1 1 0), (1 1 2) and (1 1 1) crystal-melt interfaces during unidirectional growth by in situ observation. It was directly observed that the morphology of the Si (1 1 0) and (1 1 2) crystal-melt interfaces was transformed from planar to zigzag facets at high growth velocities, although no such morphological transformation was observed at Si (1 1 1) interfaces. It was shown that a zigzag faceted interface was formed when a wavy perturbation was introduced into the planar interface, and that the perturbation was amplified. This zigzag facet formation behavior of the Si (1 1 0) and (1 1 2) interfaces is similar to that of the Si (1 0 0) interface. It is concluded that this formation of a zigzag faceted interface is universal at the crystal-melt interface of rough planes of Si, and that a negative temperature gradient at the crystal-melt interface is required for morphological transformation from planar to zigzag facets.