High-resolution x-ray diffraction strain-stress analysis of GaN/sapphire heterostructures

On the basis of high-resolution x-ray diffraction measurements, the strain-stress analysis of GaN/(00.1)α-Al2O3 heteroepitaxial structures grown by molecular beam epitaxy is performed. The deformation state of the heteroepitaxial structures is investigated depending on the relative content of N in the Ga1-xNx buffer layer with the given thickness (=4 nm) and growth conditions. Using the extrapolating technique, the a- and c-lattice parameters, as well as the in-plane and out-of-plane strains (of the order of -10-3 and 10-4, respectively) are determined for GaN epilayers from θ-2θ x-ray diffraction spectra. For GaN epilayers, both the biaxial in-plane and in-depth strains (of the order of -10-3 and 10-3, respectively) and the hydrostatic strain component (of the order of -10-4) are extracted from the measured strains. It is supposed that the hydrostatic strain in the epilayers is caused by native point defects. The maximal level for the biaxial stress in the GaN epilayer, -1.3 GPa, is achieved for the sample with a relative content, x = 0.377, of N in the Ga1-xNx buffer layer.