Vertical Bridgman growth of sapphire—Seed crystal shapes and seeding characteristics

•The growth of sapphire by the traditional vertical Bridgman (VB) method was studied by using various shapes of seed: thin, tapered and full-diameter.•Factors relating seed type to single-crystal growth are discussed, including the reproducibility of seeding processes, and the generation and elimination of low-angle grain boundaries (LAGBs).•What was learned facilitated the subsequent growth of large-diameter, 3-, 4- and 6-in., c-axis single-crystal sapphires from full-diameter seeds.

The growth of sapphire by the traditional vertical Bridgman (VB) method was studied by using various shapes of seed crystals and tungsten (W) crucibles shaped to match the seeds. Approximately 2-in. diameter, c-axis sapphire single crystals were reproducibly grown from three kinds of seed: thin, tapered and full diameter. Factors relating seed type to single-crystal growth are discussed, including the reproducibility of seeding processes, and the generation and elimination of low-angle grain boundaries (LAGBs). What was learned facilitated the subsequent growth of large-diameter, 3-, 4- and 6-in., c-axis single-crystal sapphires from full-diameter seeds.