Under electron irradiation, nanopipes in GaN were found to evolve into the so-called bamboo structure and eventually into a chain of voids. Here, the driving mechanism for this morphological evolution was examined by using transmission and scanning transmission electron microscopic studies of undoped GaN grown by hydride vapor phase epitaxy. Irradiation using various beam energies showed that morphological evolution occurred below the threshold for direct knock-on damage, and that voids migrated towards the beam. It was proposed that these observations could be explained by the stimulated diffusion of point defects. In areas relatively unexposed to electrons, a survey of core character, diameter and depth into the layer suggested that a similar process occurred by post-growth annealing, i.e. due to point defects mobile at the growth temperature. The implications of these results for understanding dislocation core structures were assessed.

Electron Irradiation and the Equilibrium of Open Core Dislocations in Gallium Nitride. M.Hawkridge, D.Cherns, Z.Liliental-Weber: Physica Status Solidi B, 2008, 245[5], 903-6