Editors : S.P. DenBaars, B.K. Meyer, S. Nakamura, F.A. Ponce, S. Strite
a1 Laboratoire d'Etudes et de Recherches sur les Matériaux, Institut des Sciences de la Mati~re et du Rayonnement, UPRESA-CNRS 6004, 6 Bd du Mardchal Juin 14050 Caen Cedex France, firstname.lastname@example.org
The best layers of GaN grown on SiC or sapphire contain high densities of threading dislocations, which do not seem to exhibit a critically important electrical activity. It is possible that the electrical activity of these dislocations may change with time. The large majority of the threading dislocations are a type, with 1/3 <1120> Burgers vector and their line parallel to the  growth direction. The atomic structure of the a threading dislocations was found to correspond to 5/7 or 8 atoms rings core with rather equal frequency. The 8 atoms ring cores contain dangling bonds and will present favourable sites for atomic impurities which eventuallly can modify the good performances of the devices.