Three types of threading dislocation in (00▪1) GaN films (c, c+a, and a-type) were observed to have hollow cores, depending on the method of growth and on the presence of electrical dopants or other impurities. High-resolution imaging and electron energy loss spectroscopy studies were discussed here which showed that open-core screw dislocations in GaN films grown by hydride vapor phase epitaxy have surfaces that were substituted by O. It was argued that open core formation was not primarily driven by the need to reduce strain field energy, but was influenced by kinetic factors, with O stabilizing the open core surfaces and acting as a growth inhibitor. It was pointed out that impurity segregation could explain a range of observed dislocation core structures in GaN. The significance of O segregation for understanding the electronic properties of dislocations in GaN was briefly discussed.

Open Core Threading Dislocations in GaN Grown by Hydride Vapour Phase Epitaxy. D.Cherns, M.E.Hawkridge, Philosophical Magazine, 2006, 86[29-31], 4747-56