Voids engulfment in shaped sapphire crystals

In shaped crystals besides the usual structural defects, such as dislocations, faceting, and grain boundaries, so-called “voids” have been observed almost always; this defect affects especially the optical quality of the crystals. The influence of growth conditions on size and distribution of trapped gas bubbles in shaped sapphire crystals has been studied both experimentally and by numerical simulation of the fluid flow in the meniscus. The influence of the pulling rate, of the ambient temperature and of the shaper design has been taken into account.