1.8 MeV He+ion backscattering and channeling was used to study various lattice matched and mismatched ScxYb1−xAs and ScyEr1−yAs films grown on GaAs (001). The lattice matching leads to excellent epitaxy with &khgr;minas low as 1.5% along the [001] direction. It is demonstrated unambiguously that the interface peaks result from the first atoms of the Ga rows of the substrate, indicating that the As sublattice is continuous across the rare‐earth monoarsenide/GaAs interface. These lattice matched heterostructures are proposed as ideal tools for studying ion channeling phenomena. Concerning the mismatched heterostructures, it is shown that the mosaic resulting from the strain relaxation, and the lattice tilt occurring for thick films can be evaluated directly from aligned spectra.