Observation of negative-U centers in 6H silicon carbide

Two negative-U centers in 6H SiC have been observed and characterized using capacitance transient techniques. These two defects give rise to one acceptor level (−/0) and one donor level (+/0) each in the band gap. The donor and the acceptor level have inverted ordering, i.e., the thermal ionization energy of the acceptor level is larger than that of the donor level. Direct evidence for the inverted ordering of the acceptor and donor levels and temperature dependence studies of the electron capture cross sections of the acceptor levels are presented.