Bubble formation in sapphire single crystals

Sapphire single crystal was grown by micro-pulling and shoulder at cooled center (SAPMAC) technique and the air bubbles were observed as one of the main defects in the as-grown crystals. Based on the growth parameters, the formation mechanism of the bubbles was discussed in the view of the crystal growth kinetics. It suggests that optimizing the temperature distribution in the furnace, selecting a suitable growth velocity and adopting a slightly convex interface to the melt can effectively reduce the quantity of bubbles.