Anisotropic Stresses in GaN Layers on an r-Al.sub.2O.sub.3 Substrate during Hydride Vapor Phase Epitaxy

We report on the fabrication of nonpolar GaN(11â20) structures by hydride vapor phase epitaxy using an AlN buffer layer synthesized by metalorganic vapor-phase epitaxy on an r-Al.sub.2O.sub.3 substrate. It is shown that the elastic stresses in the GaN(11â20)/r-Al.sub.2O.sub.3 structure in the directions of the c and a axes of the layer have different values, correlate with the full widths at half maximum of the rocking curves in the X-ray diffraction spectra in these directions, and are caused by the anisotropy of the thermal expansion coefficients of the layer and substrate lattices.