The interfacial microstructure in GaN nucleation layers was investigated by using synchrotron X-ray scattering and transmission electron microscopy. It was found that tensile-strained aligned interfacial domains coexisted with misaligned domains in an as-grown nucleation layer of mostly cubic stacking. The tensile strain originated in a 6/7 matched interfacial structure, in which 6 Ga-atomic distances in GaN were matched to 7
Al-atomic distances in sapphire. The tensile state of the aligned interfacial domains was preserved during annealing at up to 1100C, while the stacking sequence changed from cubic to hexagonal. The correlation length of the stacking order was rather short (about 0.9nm in the hexagonal phase) as compared to that (about 2.5nm) of the cubic phase in the as-grown nucleation layer, due to stacking faults which were generated during the kinetically limited transformation.

In-Plane Tensile-Strained Interfacial Structure in a GaN Nucleation Layer on Sapphire (0001). C.C.Kim, J.H.Je, M.S.Yi, D.Y.Noh, P.Ruterana: Journal of Applied Physics, 2001, 90[5], 2191-4