The ground state of silicon vacancies in 6H-SiC and 15R-SiC

We investigated irradiated 6H-silicon carbide (SiC) and 15R-SiC with the magnetic circular dichroism of the absorption (MCDA) and MCDA-detected electron paramagnetic resonance (EPR). In neutron- and electron-irradiated 6H-SiC, we observed two MCDA transitions at photon energies of 1.435 and 1.369 eV. Photoluminescence (PL) lines at these photon energies (the so-called V1 and V3 lines) are presently assigned to the neutral silicon vacancy at the two quasicubic lattice sites in 6H-SiC. In electron-irradiated 15R-SiC, which has three inequivalent quasicubic lattice sites, we observed three MCDA lines at 1442, 1438 and 1373meV, respectively. At the photon energy expected for the hexagonal site in 6H-SiC (the so-called V2 PL line), no MCDA signal was observed. From the temperature and field dependence of the MCDA. a spin S = 1/2 the quasicubic sites was determined. EPR spectra detected via these MCDA lines consist of single EPR lines at g = 2.005(2). We conclude that the ground state of V-si giving rise to these optical transitions is paramagnetic with S = 1/2 which is predicted theoretically for the ground state of the triply negative charge state. The previous assignment of the optical transitions to the neutral charge state must, therefore, be corrected. (C) 2001 Elsevier Science B,V. All rights reserved.