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 coexist with misaligned domains in an as-grown nucleation layer of mostly cubic stacking. The tensile strain originates in a 6/7 matched interfacial structure, wherein 6-Ga atomic distances in GaN match to 7-Al atomic distances in sapphire. The tensile state of the aligned, interfacial domains was preserved during annealing to 1100C, while the stacking sequence changed from cubic to hexagonal order. The correlation length of the stacking order was rather short, ~9Å in the hexagonal phase, compared to that of the cubic phase in the as-grown nucleation layer, ~25Å, due to stacking faults 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