Observation of Gas Bubble Incorporation during Micropulling-Down Growth of Sapphire

Quite often sapphire shaped crystals contain specific defects called bubbles of average diameter higher than 100 mu m or microbubbles of diameter smaller than 10 mu m. These defects strongly affect the crystal properties. Bubbles of 100 mu m in diameter have been observed in the molten zone during micropulling-down of sapphire fibers. Before their incorporation inside the crystal, they show a periodic oscillation and consequently deform the crystallization interface. These observations are discussed with reference to the available literature.