Nickel in silicon studied by electron paramagnetic resonance

We have investigated nickel in silicon samples with a wide range of initial doping concentrations by EPR, DLTS and photo-EPR techniques. Our results show that the two different Ni-centers which were observed previously by EPR, but whose structure could not be interpreted unambiguously, are both associated with Ni in a substitutional position. They are distinguished by their charges and by slightly different displacements from the ideal substitutional site. A model for the Nis+-center is suggested which explains the symmetry of this center.