ABSTRACT
Screw dislocations in gallium nitride grown by hydride vapor phase epitaxy (HYPE) and molecular beam epitaxy (MBE) have been studied using transmission electron microscopy. 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. Determination of dislocation core structure from plan-view samples was carried out using a modified 300keY field emission Philips electron microscope to obtain high resolution focal series with a constant defocus step. In the HYPE grown material screw dislocations are decorated by voids. In MBE grown materials, dislocation cores appear to be stoichiometric. However, in the HYPE grown material some high intensity columns were observed within the dislocation core. Based on comparison with image calculations from model structures, it was concluded that the presence of gallium could be assigned to these atomic positions.
