Observation of defect structure in ScAlMgO4 crystal using X-ray topography

Abstract

We examined the defect structure in a ScAlMgO4 (SAM) crystal intended for use as a substrate of GaN using synchrotron X-ray topography. No dislocations were observed in 70% of the 40 mm SAM wafer, indicating a wide dislocation-free region. The remaining 30% of the wafer was composed of high and ultra-high dislocation density regions. Two types of dislocations, straight-type and stream-type dislocations, along the [011¯0], [11¯00], and [101¯0] directions, were predominantly present in the high dislocation density region. The dislocation colonies with only straight-type or stream-type dislocations were observed and the high dislocation density region was occupied by these colonies. The lattice strains of the wafer center region that had no dislocations and the wafer edge region that had an ultra-high dislocation density weren’t uniform. The SAM crystal had unique structures such as a wide dislocation-free region, straight-type and stream-type dislocations, formation of dislocation colonies, and lattice strains that weren’t uniform.