[en] A thin AlGaN layer, which is suitable for structural study using Rutherford backscattering (RBS)/channeling, was grown on an Al₂O₃(0 0 0 1) substrate by metalorganic chemical vapor deposition. The results show that the composition of the epilayer is Al_0.05Ga_0.95N and that although the epilayer is very thin (79 nm), it has a good crystalline quality (χ_min=1.9%). The azimuthal orientation of the AlGaN epilayer relative to the Al₂O₃ substrate is AlGaN[0 0 0 1] // Al₂O₃[0 0 0 1] and AlGaN{1 1 2-bar 0} // Al₂O₃{1 0 1-bar 0}, showing that the AlGaN epilayer is rotated by 30 deg. around the [0 0 0 1] axis with respect to the Al₂O₃ substrate which decreases the lattice mismatch between the epilayer and the substrate significantly. RBS angular scan was used to determine the strain-induced tetragonal distortion of the epilayer. Combined with X-ray diffraction, the perpendicular and parallel elastic strains of the AlGaN layer, e^{perpendicular}=+0.31% and e^parallel=-0.28%, can be calculated