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 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 is preserved during annealing to 1100 degreesC, while the stacking sequence changes from cubic to hexagonal order. The correlation length of the stacking order is rather short, similar to9 Angstrom in the hexagonal phase, compared to that of the cubic phase in the as-grown nucleation layer, similar to 25 Angstrom, due to stacking faults generated during the kinetically limited transformation. (C) 2001 American Institute of Physics.