Open core threading dislocations in GaN grown by hydride vapour phase epitaxy

Three types of threading dislocation in (0001) GaN films (c, c+a, and a-type) have been observed to have hollow cores, depending on the method of growth and on the presence of electrical dopants or other impurities. In this paper, we discuss high-resolution imaging and electron energy loss spectroscopy studies which show that open core screw dislocations in GaN films grown by hydride vapour phase epitaxy have surfaces that are substituted by oxygen. It is argued that open core formation is not primarily driven by the need to reduce strain field energy, but is influenced by kinetic factors, with oxygen stabilizing the open core surfaces and acting as a growth inhibitor. It is pointed out that impurity segregation can explain a range of observed dislocation core structures in GaN. The significance of oxygen segregation for understanding the electronic properties of dislocations in GaN is briefly discussed.