A Transmission Electron Microscopy Observation of Dislocations in GaN Grown on (0001) Sapphire by Metal Organic Chemical Vapor Deposition

A transmission electron microscopy (TEM) observation of dislocations in GaN grown on (0001) sapphire by metal organic chemical vapor deposition (MOCVD) was carried out in this study. The GaN film was rotated 30° around the c-axis in the growth plane against the substrate. The finding of this research, according to TEM analysis, is that about 3% (or less) of the threading dislocations are pure screw (b = <0001 >) and 20% are pure edge (b = 1/3 <1120 >). The remaining threading dislocations, about 77%, are mixed-type dislocations; that is the major dislocation type in the GaN epitaxial layer grown on (0001) sapphire is the mixed type. In addition, to further understand the dislocation configuration on the interface of GaN/sapphire, a plane-view TEM sample of the GaN/sapphire interface was prepared. The plane-view TEM image of the GaN/sapphire interface reveals an extremely high density of kink dislocations lying on the interface, with a dislocation density of about 8×10⁹ cm^-2, involving high strain and stress. A comparison of the 8×10⁹ cm^-2 dislocation density with another plane-view TEM image (6×10⁸ cm^-2) near the GaN free surface revealed that approximately 7.5% of the dislocations lying on the substrate coalesce into threading dislocations generated from the interface to the GaN surface.