Seed orientation and pulling rate effects on bubbles and strains distribution on sapphire crystal grown by micro-pulling down method

Undoped sapphire rods crystals (ɸ = 3mm, length ≈170mm) along different crystallographic orientations (a [11¯20], m [10¯10], c [0001] and c [0001] shifted of 30° axis), were successfully grown by micro-pulling down (μ-PD) method. Bubbles defects distribution were investigated as a function of thermal gradient and pulling rates. It is observed that sapphire rods grown at low pulling rate (v<200µm/min) were bubbles free. Homogeneous temperature distribution around the capillary die will limit the bubbles propagation. Pulling sapphire rods along c-axis is a good way to minimize bubbles propagation. The growth parameters effects on bubbles and strain distribution in sapphire rods grown by µ-PD rods was discussed.