Band-gap states of Ti, V, and Cr in4H-SiC: Identification and characterization by elemental transmutation of radioactive isotopes

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 ${}^{48}\mathrm{V}$ or ${}^{51}\mathrm{Cr}$ by recoil implantation and annealing at 1600 K. These isotopes decay to ${}^{48}\mathrm{Ti}$ or ${}^{51}\mathrm{V}$ 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 ${}^{51}\mathrm{V}.$ Titanium is found to have a slightly split acceptor state (0.13 and 0.17 eV below the conduction-band edge $E_C$) 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 $E_C$) in the range investigated with an indication of splitting. Cr has three levels: two of them closely spaced at $E_C-0.14$ and $-0.18\mathrm{eV}$ are interpreted as a slightly split double acceptor state and one level at $E_C-0.74\mathrm{eV}$ 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 $E_C-0.97\mathrm{eV}.$ This finding is discussed in terms of different structural configurations.