Two electron paramagnetic resonance spectra, which were present in p-type samples after doping with Ag, were reported. The 2 centers exhibited a symmetry which was lower than cubic, and had an effective electron spin of S = ½. Because of a hyperfine interaction with nuclear spins of I = 3/2, the spectra were attributed to a contaminant that had been introduced into the samples during diffusion. By analyzing features of the spectrum, and defect formation, a spectrum of tetragonal symmetry (Si-NL58) was attributed to a Cu-Cu pair in a negatively charged state. The other spectrum (Si-NL59) was attributed to a complex which contained one Cu atom.

P.N.Hai, T.Gregorkiewicz, C.A.J.Ammerlaan, D.T.Don: Physical Review B, 1997, 56[8], 4620-5