Pseudomorphic Si1-x-yGexCy/Si superlattice structures on Si were prepared by molecular beam epitaxy in the compositional range : 8 < x < 44% and 0 < y < 4.4%, with layer thicknesses between 5 and 35 nm. Comprehensive materials characterization was carried out by Rutherford and C-resonance backscattering combined with ion channeling. Complementary analysis was provided by secondary ion mass spectrometry (SIMS) and high-resolution transmission electron microscopy. The Si1-x-yGexCy layer composition was derived by measuring the average Ge and C concentrations by ion backscattering and the layer thicknesses from electron micrographs. Carbon depth profiles of good sensitivity were derived from SIMS profiling. The superlattice strain was measured by X-ray diffraction and usually found to be compressive. However, lattice-matched and tensile superlattice films were obtained for alloys with similar to 10% Ge. The tensile him bad growth defects - microtwins and stacking faults - which could be observed by TEM and detected by ion channeling.