The effect of coalescence on threading dislocations in GaN films

The effect of the coalescence of islands on threading dislocations (TDs) in GaN films (300 nm thick) grown on non-annealed and annealed sapphire substrates has been studied. Atomic force microscopy measurements show that the a-type TD density first decreases and then increases during the coalescence process, while the densities of (a + c)- and c-type TDs decrease as coalescence proceeds. X-ray diffraction data indicate that the lattice tilt of GaN films is greatly reduced by coalescence while the change in twist depends on the degree of coalescence.