Investigation of the atomic structure of the pure edge and a+c threading dislocations in gan layers grown by MBE

The active layers of GaN contain high densities of threading dislocations, which do not seem to exhibit important electrical activity. It is possible that this may change with time. About 90% are a type, with 1/3 112̄0 Burgers vector and their line parallel to the [0001] growth direction, the remaining 10% are a+c and pure edge c dislocations. High resolution electron microscopy investigation shows that the atomic structure of the a threading dislocations corresponds to 5/7 or eight atom ring cores with rather equal frequency. In modelling the a+c dislocation, it is shown that only the a component is visible in the images along the [0001], and that the effect of the screw component is spread symmetrically all over the area surrounding the dislocation core.