Relationship between defects induced by irradiation and reduction of hole concentration in Al-doped 4H-SiC

From the temperature dependence of the hole concentration in lightly Al-doped 4H-SiC epilayers, a shallow acceptor with EV+0.2eV, which is an Al atom (AlSi) at a Si sublattice site, and an unknown deep defect with EV+0.35eV are found, where EV is the valence band maximum. In unirradiated epilayers, moreover, the density (NDefect) of this defect is close to the Al acceptor density (NAl). With irradiation of 0.2 MeV electrons, the NAl is reduced, while the NDefect is increased. Judging from the minimum electron energy required to displace a substitutional C atom (Cs) or AlSi, the bond between AlSi and its nearest neighbor Cs is broken due to the displacement of the Cs by this irradiation. Moreover, the displacement of the Cs results in the creation of a complex (AlSi-VC) of AlSi and its nearest neighbor C vacancy (VC), indicating that the possible origin of the defect with EV+0.35eV is AlSi-VC.