The first direct observations of the atomic structures of threading dislocation cores in the hexagonal phase of GaN were presented. By using atomic-resolution Z-contrast imaging, dislocations with edge character were found to exhibit an 8-fold ring core. The central column in the core of a pure edge dislocation had the same configuration as one row of dimers on the {10-10} surface. On the basis of published theory, it was proposed that edge dislocations did not have deep defect states in the band-gap, and did not contribute to cathodoluminescence dislocation contrast. On the other hand, both mixed and pure screw dislocations were found to have a full core, and full screw dislocation cores were predicted to have states in the band-gap.

Y.Xin, S.J.Pennycook, N.D.Browning, P.D.Nellist, S.Sivananthan, F.Omnès, B.Beaumont, J.P.Faurie, P.Gibart: Applied Physics Letters, 1998, 72[21], 2680-2