GaAs/AlxGa1-xAs multiple-quantum-well structures with identical well thicknesses (almost-equal-to 119 angstrom) but with different Al contents x in the barrier (x almost-equal-to 0. 1, 0.2, 0.45, and 1) were grown by molecular-beam epitaxy. We report the characterization of the structures by a combination of different techniques. The x-ray-diffraction technique allows us to estimate the Al content x and to measure the period of the structure with good accuracy. Using the photographs given by high-resolution transmission electron microscopy on cleaved wedges, we investigate directly the key parameters of the structures, such as the regularity, the layer thickness, and the Al content x. The photoluminescence measurements carried out in detail from 4 K to room temperature show the excitonic character of the radiative recombination in these structures up to room temperature. The influence of x on the photoluminescence is investigated systematically. The data confirm the theoretical results calculated using finite barrier heights. The increase of transition energies with increasing x is due to the increase of confinement energies and exciton binding energies. A good agreement of the structure parameter values obtained by the above techniques is given.