A method was described for growing large single crystals, from the melt, which were completely free of low-angle grain boundaries. This perfection was achieved by eliminating the localized cellular structures which were introduced by thermal supercooling due to faceted growth. These defects were distributed only near to the developed (012)h and (01¯2¯)h planes when the growth of these planes as facets could be reduced rapidly in the conical part of the boule. Low-angle grain boundaries along the z-axis, and the polygonization of dislocations, were caused by stresses around the cellular structure. The observation of cellular structures indicated that their formation was strongly dependent upon growth in the radial direction and upon the pulling rate. In order to eliminate these structures, it was found to be most effective to keep the crystal growth rate to less than 10mm/h.

T.Suzuki: Journal of Materials Science, 1995, 30[11], 2873-6