Continuous-wave and pulsed EPR study of the negatively charged silicon vacancy with S=3/2 and C3v symmetry in n-type 4H-SiC -: art. no. 235202

The T-V2a center, which was suggested to be the excited triplet state (S=1) of the neutral silicon vacancy related defect [Sorman et al., Phys. Rev. B 61, 2613 (2000)] in the electron-irradiated n-type 4H-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 C-13 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.