Morphology of threading dislocations  in GaN films with different resistivities grown on sapphire by means of metal organic chemical vapour deposition was investigated using transmission electron microscopy. Films with different resistivities were achieved at various annealing pressures of the nucleation layer. It was observed that the threading dislocations were almost all straight and perpendicular to the sapphire surface in high-resistivity GaN films, while they were significantly bent and interactive in low-resistivity GaN films. The analysis results based on the X-ray diffractometry and transmission electron microscopy demonstrate that the density and morphology of threading dislocations change with annealing pressure of the nucleation layer. It was concluded that the annealing pressure of the nucleation layer effectively controls the size, density, and coalescence rate of the islands, and thus determines the density and morphology of threading dislocations in GaN.

Morphology of Threading Dislocations in High-Resistivity GaN Films Observed by Transmission Electron Microscopy. L.Lu, B.Shen, F.J.Xu, J.Xu, B.Gao, Z.J.Yang, G.Y.Zhang, X.P.Zhang, J.Xu, D.P.Yu: Journal of Applied Physics, 2007, 102[3], 033510