Band-gap states of Ti, V, and Cr in 4H -SiC: Identification and characterization by elemental transmutation of radioactive isotopes

This is the authors' abstract. We don't add key points for this paper.

Band-gap states in $4H$-silicon carbide (SiC) are created by radioactive isotopes and detected by repeated deep-level transient spectroscopy measurements. Band-gap states involving a parent or a daughter isotope are uniquely identified by their decreasing or increasing concentration during the nuclear transmutation. Epitaxial layers of n-type $4H$-SiC are doped with ⁴⁸V or ⁵¹Cr by recoil implantation and annealing at 1600 K. These isotopes decay to ⁴⁸Ti or ⁵¹V with half-lives of 16.0 or 27.7 d, respectively. The stability of daughter atom configurations is probed by annealing after the transmutation and found to be unstable in the case of ⁵¹V. Titanium is found to have a slightly split acceptor state (0.13 and 0.17 eV below the conduction-band edge EC) and the splitting is attributed to the occupation of the two inequivalent lattice sites of $4H$-SiC. Vanadium has one level only (0.97 eV below EC) in the range investigated with an indication of splitting. Cr has three levels: two of them closely spaced at EC-0.14 and -0.18eV are interpreted as a slightly split double acceptor state and one level at EC-0.74eV as the corresponding single acceptor state of the same configuration. Within errors, all Ti and Cr atoms form the band-gap states described whereas in the case of V a minority of all atoms only contributes to the band-gap state at EC-0.97eV. This finding is discussed in terms of different structural configurations.