The electronic properties of a H-related radiation-induced defect in crystalline material were investigated. Strong evidence was presented for the suggestion that the center had negative-U properties, with a shallow donor level (0/+) at Ec - 0.043eV above a deep acceptor level (-/0) at Ec - 0.11eV. The optical ionization energy of the defect in the acceptor state was found to be 0.38eV; and thus higher than the thermal ionization energy. It was shown that 2 atomic configurations, separated by an energy barrier, were available for the center. Due to the existence of this barrier, features which were related to the metastable neutral charge state of the defect were observed at low temperatures. On the basis of the results, a configurational coordinate diagram for the center was constructed.

V.P.Markevich, I.F.Medvedeva, L.I.Murin, T.Sekiguchi, M.Suezawa, K.Sumino: Materials Science Forum, 1995, 196-201, 945-50