Epitaxial (00•1) GaN layers were grown, using molecular beam epitaxy, onto nm-thick low-temperature GaN nucleation layers on c-plane sapphire. In spite of an extremely high density of extended defects, the layers exhibited a narrow (002) X-ray diffraction peak and superposed broad diffuse scattering. Triple-axis transverse and radial scans were performed for (00l) reflections of different orders and for various GaN layer thicknesses. The results could be described by an interfacial displacement difference correlation function. Its origin was attributed to inversion domain boundaries or edge-type threading dislocations in the GaN layers; in agreement with the findings of transmission electron microscopy. The defects were associated with a weak rotational disorder, perpendicular to the growth plane, as demonstrated by the X-ray scattering characteristics.

X-Ray Scattering from GaN Epitaxial Layers - an Example of Highly Anisotropic Coherence. H.Heinke, V.Kirchner, H.Selke, R.Chierchia, R.Ebel, S.Einfeldt, D.Hommel: Journal of Physics D, 2001, 34[10A], 25-9