The defects in hexagonal GaN epitaxial layers grown on (00•1) sapphire (Al2O3) substrates by HVPE with a horizontal tube reactor were studied. The GaN epitaxial layers were etched by means of defect-selective etching (Orthodox etching in molten KOH). The samples were characterized by scanning electron microscopy and Cathodoluminescence spectra. From surface morphology and cross-sectional images, the defects could be divided into various types: cracks, low-angle grain boundary, nano-pipes and dislocations. These different defects were analyzed. The cracks were proposed to be related to the strain. And the strain could not only come from the lattice mismatch and thermal mismatch between sapphire and GaN layer in their interface, but also from the HVPE growth process. It was found that these screw, mixed and edge type dislocations formed small hexagonal pits after etching. Some pits would be observed in the area near low-angle grain boundaries. Additionally, by cathodoluminescence mapping technique, some non-radiative recombination centers without surface terminations could be probed optically.

Study of the Defects in GaN Epitaxial Films Grown on Sapphire by HVPE. Z.Liu, X.Xiu, L.Chen, R.Zhang, Z.Xie, P.Han, Y.Shi, S.Gu, Y.Zheng: Proceedings of the SPIE, 2008, 6984, 698423