Defect structure of a free standing GaN wafer grown by the ammonothermal method

•Synchrotron radiation X-ray topography study of ammonothermal GaN.•Results show low dislocation density within grains.•Grain tilt and twist were estimated using synchrotron radiation X-ray topography.•Threading mixed and screw dislocations were identified while no pure threading edge dislocations were observed.

White beam synchrotron radiation X-ray topography (SR-XRT) and X-ray diffraction (XRD) measurements were used to non-destructively study the defect structure of a bulk GaN wafer, grown by the ammonothermal method. SR-XRT topographs revealed high crystal quality with threading dislocation density 8.8×104 cm−2 and granular structure consisting of large, slightly misaligned grains. The threading dislocations within grains were identified as mixed and screw type, while no pure threading edge dislocations were observed.