It was pointed out that active layers contained high densities of threading dislocations which did not seem to exhibit any significant electrical activity. Some 90% of them were of a-type, with a 1/3<11•0> Burgers vector and with their line parallel to the [00•1] growth direction. The remaining 10% were a+c and pure edge c-type dislocations. High-resolution electron microscopic investigations showed that the atomic structure of the a-type threading dislocations corresponded to 5, 7 or 8-atom ring cores in roughly equal numbers. Upon modelling the a+c dislocation, it was shown that only the a-component was visible in images taken along [00•1], and that the effect of the screw component was spread symmetrically over all of the area surrounding the dislocation core.

Investigation of the Atomic Structure of the Pure Edge and a+c Threading Dislocations in GaN Layers Grown by MBE. P.Ruterana, V.Potin, G.Nouet, R.Bonnet, M.Loubradou: Materials Science and Engineering B, 1999, 59[1-3], 177-81