In this paper, we present results of ion-beam and X-ray characterization of SiGeC compound semiconductor films, which are at an important development stage at the moment. We first certify the sensitivity of non-Rutherford resonant ion scattering for detection of minimal carbon concentration in the films, then we present clear evidence of strain relaxation by introduction of a small amount of carbon into SiGe films, and finally we discuss the lattice location of C atoms.