Proton-irradiation-induced electronic defects in relaxed, epitaxial p-type Si1-xGex layers grown by molecular-beam epitaxy have been investigated by deep level transient spectroscopy (DLTS) for 0⩽x⩽0.25. Three dominating lines in the DLTS spectra have been observed and correlated to the divacancy, interstitial carbon, and the interstitial-boron–substitutional-carbon pair. For all three levels the activation enthalpy relative to the valence band decreases with increasing Ge content. Annealing studies demonstrated that the annealing of the defect level, identified as interstitial carbon, is retarded with increasing Ge content, while the annealing temperatures of the two other defects are similar to those observed in silicon. © 1997 American Institute of Physics.