Surface Defects in EFG Sapphire Single Crystals

Single crystal growth by the edge-defined film-fed growth method (EFG) has been commercially practiced for over 40 years. State of the art sapphire crystals can be over 300 mm wide, 10 mm thick and 1 m long. In addition to well-known defects such as bubble inclusions and bulk structure loss, we describe a crystalline defect occurring uniquely at the outer surfaces of the sapphire panel. Termed 'surface crystals', they penetrate less than 1 mm into the depth of the A-plane panel and can originate and terminate multiple times in a single panel. We report correlations with both temperature and ambient conditions and present micro-scale characterization to elucidate the nature of these defects.