Depending on the thickness and the lattice mismatch, the semiconductor multi-layers can accommodate strain (for small thicknesses) and relax into dislocations (for large thicknesses). The energetic ion beams with suitable energies can probe these multi-layers nondestructively with respect to their defects concetrations as well as the strain determination. As is well known that this information is crucial for band gap engineering of the superlattices. Some detailed calculations and recent experimental results will be presented.