The electrical and optical properties of defects due to ion implantation of ruthenium in silicon have been studied by means of junction space‐charge techniques. Two energy levels were observed with energy positions atEc−0.184 eV (A‐level) andEV+0.265 eV (B‐level), respectively, at 77 K. The changes in enthalpy due to the capture of electrons and holes were −8 meV (A‐level) and 1 meV (B‐level). Gibb’s free energies at different temperatures were calculated for both levels. Good agreement with the corresponding optical threshold energy was found for theB‐level suggesting a small Frank–Condon shift. A tentative model for the origin of the observed defects is discussed. ©1995 American Institute of Physics.