High-resolution X-ray diffraction of molecular-beam-epitaxy-grown InAlAs/InGaAs/InAlAs three-layer structures on (001)-oriented InP substrates

High-resolution X-ray diffraction was used to evaluate a number of three-layer structures of InAlAs/ InGaAs/InAlAs, which were grown on (001) InP by molecular-beam epitaxy. The aim was to determine the influence on the rocking curve of the InGaAs layer between the two InAlAs barriers. Very sharp and well defined thickness oscillations up to the 20th order show the high quality of the samples. It was possible to prove the existence of an InAs-rich InAsP layer with a thickness of 0.2-0.8 nm between the substrate and the first InAlAs layer. The transitions between the InGaAs layer and the two InAlAs barriers are characterized by a concentration gradient. This structure, which deviates from the ideal one, was very well suited to the matching of rocking-curve simulations based on the dynamical theory of X-ray diffraction with the experimental 004 and 115 reflection curves.