A bulk GaN crystal with improved structural quality was grown via ammonthermal growth with polycrystalline GaN nutrient and a sodium amide mineralizer. The threading dislocation density estimated by plan-view transmission electron microscopy observations was less than 106/cm2 for the Ga-face and 107/cm2 for the N-face. There was no dislocation generation observed at the interface on the Ga-face although a few defects were generated at the interface on the N-face. The chemical etching revealed macroscopic grains on the N-face.

Growth of Bulk GaN with Low Dislocation Density by the Ammonothermal Method Using Polycrystalline GaN Nutrient. T.Hashimoto, F.Wu, J.S.Speck, S.Nakamura: Japanese Journal of Applied Physics, 2007, 46[22], L525-7