High precision determination of the elastic strain of InGaN/GaN multiple quantum wells

The composition, elastic strain, and structural defects of an InGaN/GaN multiple quantum well (MQW) are investigated using a combination of x-ray diffraction, transmission electron microscopy, and Rutherford backscattering/channeling. None of the applied techniques alone can unambiguously resolve the thickness of the individual layers, the In composition in the wells, and the elastic strain. These three parameters directly determine the optical properties of the MQW. It is shown that only a combination of these measurements reveals the full structural characterization of the nitride multilayer. A clear correlation between the defect density of In distribution and strain relaxation is evidenced. The experimental result of the ratio of the average perpendicular elastic strain (e-L and the average parallel elastic strain <e(\\)>, <e(perpendicular to)>/<e(\\)>= -0.52, is in excellent agreement with the value deduced from the elastic constants. (C) 2004 American Vacuum Society.