The characterization of 2 negative-U centers in 4H-type samples was performed by using various capacitance transient techniques. Each center gave rise to one acceptor level (-/0) and one donor level (0/+), where the electron ionization energy of the acceptor level was larger than that of the donor level. The 2-electron emissions from the 2 acceptor levels gave rise to a previously reported deep-level transient spectroscopy peak which was associated with the so-called Z1 center. Direct evidence was presented for an inverted ordering and temperature dependence of the electron-capture cross-sections of the acceptor levels.

Negative-U Centers in 4H Silicon Carbide. C.G.Hemmingsson, N.T.Son, A.Ellison, J.Zhang, E.Janzén: Physical Review B, 1998, 58[16], R10119-22