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

Abstract

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.