A transmission electron microscopic observation of dislocations in GaN grown onto (00•1) sapphire by metalorganic chemical vapor deposition was carried out. The GaN film was rotated 30° around the c-axis in the growth plane against the substrate. The findings of this research, according to transmission electron microscopic analysis, was that about 3% (or less) of the threading dislocations were pure screw (b = <00•1>) and 20% were pure edge (b = 1/3<11•0>). The remaining threading dislocations, about 77%, were mixed-type dislocations; that was the major dislocation type in the GaN epitaxial layers grown onto (00•1) sapphire was of mixed type. In addition, to understand further the dislocation configuration on the interface of GaN/sapphire, a plane-view transmission electron microscopic sample of the GaN/sapphire interface was prepared. The plane-view transmission electron microscopic image of the GaN/sapphire interface revealed an extremely high density of kink dislocations lying on the interface, with a dislocation density of about 8 x 109/cm2, involving high strain and stress. A comparison of the 8 x 109/cm2 dislocation density with another plane-view transmission electron microscopic image (6 x 108/cm2) near to the GaN free surface revealed that approximately 7.5% of the dislocations lying on the substrate coalesced into threading dislocations generated from the interface to the GaN surface.

A Transmission Electron Microscopy Observation of Dislocations in GaN Grown on (0001) Sapphire by Metal Organic Chemical Vapor Deposition. S.Y.Huang, J.R.Yang: Japanese Journal of Applied Physics, 2008, 47, 7998-8002