Development of a three-dimensional-micro-pulling-down method and growth of spring-shaped sapphire single crystals

Abstract

A three-dimensional-micro-pulling-down (3D-μ-PD) method was developed for the growth of 3D shaped single crystals, and spring-shaped sapphire single crystals were grown by the 3D-μ-PD method using Mo crucibles with different dies. The shape of the die significantly affected the growth stability and shape control of the spring-shaped single crystals. Spring-shaped sapphire single crystals with a smaller helical pitch and larger helical radius were obtained easily using a Mo crucible with a sharp conical die compared to that with a blunt conical die. However, spring-shaped sapphire single crystals grown using a Mo crucible with an inverse conical die can be obtained with smaller helical pitches, and the shape of the cross-sectional plane is a horizontally extended elliptical shape. The difference in the shape of the cross-sectional plane for spring-shaped sapphire single crystals affects the crystallinity and mechanical properties. Furthermore, crystals grown using the Mo crucible with the inverse conical die exhibited a larger shrinkage rate in the compression test.