Band-gap states of Ti, V, and Cr in 4H-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 V-48 or Cr-51 by recoil implantation and annealing at 1600 K. These isotopes decay to Ti-48 or V-51 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 V-51. 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 eV are interpreted as a slightly split double acceptor state and one level at E-C-0.74 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 eV. This finding is discussed in terms of different structural configurations. [S0163-1829(98)04019-3].