A study of screw dislocations in hydride-vapor phase epitaxy template and molecular beam epitaxy overlayers was performed by using transmission electron microscopy in plan view and in cross-section. It was observed that screw dislocations in the hydride-vapor-phase-epitaxial layers were decorated by small voids arranged along the screw axis. However, no voids were observed along screw dislocations in molecular beam epitaxial overlayers. This was true both for molecular beam epitaxial samples grown under Ga-lean and Ga-rich conditions. Dislocation core structures were studied in these samples in the plan-view configuration. These experiments were supported by image simulation using the most recent models. A direct reconstruction of the phase and amplitude of the scattered electron wave from a focal series of high-resolution images was applied. It was shown that the core structures of screw dislocations in the studied materials were filled. The filed dislocation cores in an molecular beam epitaxial samples were stoichiometric. However, in hydride-vapor phase epitaxial materials, single atomic columns exhibited substantial differences in intensities and might indicate the possibility of a higher Ga concentration in the core than in the matrix. A much lower intensity of the atomic column at the tip of the void was observed. This could suggest the presence of lighter elements, such as O, responsible for their formation.

Screw Dislocations in GaN Grown by Different Methods. Z.Liliental-Weber, D.Zakharov, J.Jasinski, M.A.O’Keefe, H.Morkoc: Microsc Microanal., 2004, 10[1], 47-54