In-plane tensile-strained interfacial structure in a GaN nucleation layer on sapphire(0001)

Interfacial microstructure in GaN nucleation layers was investigated using synchrotron x-ray scattering and transmission electron microscopy. We find that tensile-strained, aligned, interfacial domains coexist with misaligned domains in an as-grown nucleation layer of mostly cubic stacking. The tens ile 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 ten sile state of the aligned, interfacial domains is preserved during annealin g to 1100 degreesC, while the stacking sequence changes from cubic to hexag onal order. The correlation length of the stacking order is rather short, s imilar to9 Angstrom in the hexagonal phase, compared to that of the cubic p hase in the as-grown nucleation layer, similar to 25 Angstrom, due to stack ing faults generated during the kinetically limited transformation. (C) 200 1 American Institute of Physics.