Dislocation baskets in thick In_xGa_1-xN epilayers

Dislocation clusters have been observed in thick In_xGa_{1 - x}N films with 0.07 ≤ x ≤ 0.12. The clusters resemble baskets with a higher indium content at their interior. Threading dislocations at the basket boundaries are of the misfit edge type, and their separation is consistent with misfit strain relaxation due to the difference in indium content between the baskets and the surrounding matrix. The interior of the base of the baskets exhibits no observable dislocations connecting the threading dislocations, and often no net displacements like those due to stacking faults. We argue that the origin of these threading dislocation arrays is associated with misfit dislocations at the basal plane that dissociate, forming stacking faults. And when the stacking faults form simultaneously satisfying the crystal symmetry, the sum of their translation vectors add up to a lattice vector, or equivalently to no change in the stacking sequence, which is consistent with our observations.