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)alpha -Al2O3 heteroepitaxial structures grown by molecular beam epitaxy is performed. The deformation state of the hetero epitaxial structures is investigated depending on the relative content of N in the Ga1-xNx buffer layer with the given thickness (= 4 nm) and growth c onditions. Using the extrapolating technique, the a- and c-lattice paramete rs, 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 theta - 2 theta x-ray diffraction spectra. For GaN epilayers, both the biaxial in-p lane and in-depth strains (of the order of - 10(-3) and 10(-3), respectivel y) and the hydrostatic strain component (of the order of -10(-4)) are extra cted from the measured strains. It is supposed that the hydrostatic strain in the epilayers is caused by native point defects. The maximal level for t he 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.