Study on defects in large-flat sapphire crystal grown by horizontal directional solidification

The large-flat sapphire single crystal was successfully grown by horizontal directional solidification (HDS) method. The defects in grown crystal were analyzed by laser scanning confocal microscope, scanning electron microscope and chemical etching method. The macro defect types and the morphology of dislocations were observed and discussed. The distribution and formal reasons of defects were also analyzed. Bubbles and inclusions were regarded as main macro defects. The constituents of inclusions were detected by electron probe microanalysis, and formal reasons of inclusions were also investigated. The results indicated that the small inclusions of block and erose shape were formed by concentrated C and Si impurities which gathered other impurities, and the large inclusions of strip and circular shape were due to great mismatch of stoichiometric composition in O and Al elements. The morphology of dislocations in grown crystal was triangle etch pits analyzed by chemical etching method, and the dislocations form were discussed as well.