An electron paramagnetic resonance signal, labelled TU1, was found in hydrogenated Czochralski-grown crystals after irradiation with fast electrons and annealing at 300 to 400C. An isotropic g-factor of 1.9987 indicated a shallow-donor nature of the defect which gave rise to the signal. Well-resolved lines, due to the hyperfine interaction of unpaired electrons with 29Si nuclei, were detected in the TU1 spectrum. This was unusual for shallow-donor centers in Si. Such features were expected if a wave function of the unpaired electron was localized around a central Si atom of the defect. By comparing the electron paramagnetic resonance data with the results of optical and electrical measurements performed on identical crystals, it was established that the TU1 signal was related to the shallow-donor state of an H-O-related center having negative-U properties.

V.P.Markevich, T.Mchedlidze, M.Suezawa: Physical Review B, 1997, 56[20], R12695-7