The effect of the coalescence of islands on threading dislocations in GaN films (300nm-thick) grown on non-annealed and annealed sapphire substrates was studied. Atomic force microscopy measurements showed that the a-type threading dislocation density first decreases and then increases during the coalescence process, while the densities of (a + c)- and c-type threading dislocations decreased as coalescence proceeds. X-ray diffraction data indicated that the lattice tilt of GaN films was greatly reduced by coalescence while the change in twist depended on the degree of coalescence.

The Effect of Coalescence on Threading Dislocations in GaN Films. Y.Liu, J.Zhang: Scripta Materialia, 2010, 63[1], 109-12