Electronic structure of the neutral silicon vacancy in 4H and 6H SiC

Detailed information about the electronic structure of the lowest-lying exc ited states and the ground state of the neutral silicon vacancy in 4H and 6 H SiC has been obtained by high-resolution photoluminescence (PL), PL excit ation (PLE), and Zeeman spectroscopy of both PL and PLE. The excited states and the ground states involved in the characteristic luminescence of the d efect with no-phonon (NP) lines at 1.438 and 1.352 eV in 4H SiC and 1.433, 1.398, and 1.368 eV in 6H SiC are shown to be singlets. The orbital degener acy of the excited states is lifted by the crystal field for the highest-ly ing NP lines corresponding to one of the inequivalent lattice sites in both polytypes, leading to the appearance of hot lines at slightly higher energ ies. Polarization studies of the NP lines show a different behavior for the inequivalent sites. A comparison of this behavior in the two polytypes tog ether with parameters from spin resonance studies provides useful hints for the assignment of the no-phonon lines to the inequivalent sites. In strain ed samples an additional fine structure of the NP lines can be resolved. Th is splitting may be due to strain variations in the samples.