Mechanisms of reduction in hole concentration in Al-doped 4H-SiC by electron irradiation

From the temperature dependence of the hole concentration in unirradiated lightly Al-doped 4H-SiC epilayers, an Al acceptor with E_V + 0.2 eV, which is an Al atom (Al_Si) at a Si sublattice site, and an unknown deep acceptor with E_V + 0.35 eV are found, where E_V is the top of the valence band. Both the densities are similar. With irradiation of 0.2 MeV electrons the Al acceptor density is reduced, while the unknown deep acceptor density is increased. Judging from the minimum electron energy required to displace a substitutional C atom (C_s) or the Al_Si, the bond between the Al_Si and its nearest neighbor C_s is broken due to the displacement of the C_s by this irradiation. Moreover, the displacement of the C_s results in the creation of a complex (Al_Si-V_C) of Al_Si and a carbon vacancy (V_C), indicating that the possible origin of the deep acceptor with E_V + 0.35 eV is Al_Si-V_C.