Defects in GaN: core structure of screw dislocations

Screw dislocations in GaN grown by HVPE and MBE have been studied using transmission electron microscopy. It was shown that screw dislocations in the HYPE layers are decorated by small voids arranged along the screw axis, but voids were not observed along screw dislocations in MBE overlayers grown on top of the HYPE layers. A direct reconstruction of the phase and amplitude of the scattered electron wave from a focal series of high-resolution images showed that the core structures of screw dislocations in all studied materials were filled. Dislocation cores in MBE samples were stoichiometric. However, in HVPE materials, single atomic columns show substantial differences in intensities and indicate the possibility of the presence of Ga.