Composition measurement in strained $AlGaN$ epitaxial layers using x-ray diffraction

An x-ray diffraction technique is described which, by careful choice of the x-ray reflection used, minimizes errors in composition measurements resulting from strain and uncertainties in the elastic constants of a material. The method is applied to the $AlGaN$ system, which shows a wide range of values for Poisson’s ratio in the literature and significant variation in strain state due to the high dislocation content and large thermal expansion mismatch with the substrate. It is demonstrated that accurate composition measurements of partially relaxed $AlxGa1−xN$ layers $(x<0.3)$ with thickness $>20nm$ can be made from a single measurement.