Continuous-wave and pulsed EPR study of the negatively charged silicon vacancy withS=32andC3vsymmetry inn-type4H−SiC

The ${T}_{V2a}$ center, which was suggested to be the excited triplet state $(S=1)$ of the neutral silicon vacancy related defect [S\"orman et al., Phys. Rev. B $61,$ 2613 (2000)] in the electron-irradiated n-type $4H\ensuremath{-}\mathrm{SiC}$ has been studied by continuous wave and pulsed electron paramagnetic resonance (EPR). The spin multiplicity of ${T}_{V2a}$ has been determined to be quartet $(S=3/2)$ by the nutation method of pulsed EPR technique. From the temperature dependence of the signal intensity, it has been revealed that the ${T}_{V2a}$ spectrum is arising from an electronic ground state. From the measurement of the ${}^{13}\mathrm{C}$ hyperfine interactions of the nearest neighbors which has been enabled by the selective enhancement of the ${T}_{V2a}$ signals through the spin polarization by a laser light (808 nm) illumination, the center is unambiguously identified to be a single silicon vacancy. It is proposed that the center is a negatively charged silicon vacancy of ${C}_{3v}$ symmetry with the crystal field distorted slightly from regular tetrahedron. The triply degenerate ${t}_{2}$ state of an electronic configuration ${a}_{1}^{2}{t}_{2}^{3}$ under ${T}_{d}$ symmetry splits into ${a}_{1}$ and e by the distortion to ${C}_{3v}.$ The high spin configuration $[{a}_{1}{e}^{2}$ or ${e}^{2}{a}_{1}]$ which reduces the electron repulsion energy is preferred rather than the low spin configuration expected from the symmetry-lowering crystal field alone. The important role of the many-electron effect in determining the ground-state configuration is demonstrated clearly by ${T}_{V2a}$ in which the electron-electron interactions (the electronic repulsion and the electron exchange) compete against the crystal-field splitting.