Ga0.6Al0.4Sb/GaSb single-quantum-well structures grown by molecular-beam epitaxy on GaSb substrates with different well thicknesses, have been studied by high-resolution x-ray diffraction and x-ray standing-wave methods. By fitting the diffraction curves, thickness, composition, and the static Debye–Waller factor were obtained for each layer of the structures. The analysis of the angular dependence of the yield of photoelectrons emitted by the x-ray standing-wave field in the range of the dynamical x-ray diffraction was used for selecting the most appropriate set of layer parameters among those which gave virtually identical fittings of the diffraction curves. Relatively broadened GaAlSb/GaSb interfaces were found in all of the samples. This result was confirmed by high-resolution transmission electron microscopy investigation of one of the samples. The effect of the surface degradation due to the chemical reaction with the atmosphere of the free surface of the upper Ga0.6Al0.4Sb layer was considered. © 2000 American Institute of Physics.