Electronic structure of the Be acceptor centers in 6H-SiC

In this paper, we present an overview of the different shallow and deep acceptor centers in ${}^9\mathrm{Be}$-doped 6H-SiC. 95-GHz electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) measurements have been performed to determine their g, hyperfine, and quadrupole tensors and up to eight different centers were identified. The geometric and electronic structure of these centers resembles that of the B-related centers in 6H-SiC. Three of them showed the behavior characteristic of shallow B centers, five of them that of deep centers. Three of the deep centers, that have their symmetry axis along the c axis, are similar to the centers found in B-doped 6H-SiC. The two others have their symmetry axis at 70° to the c axis and have not been found in B-doped 6H-SiC. To our knowledge this is the first time that deep Be acceptor centers are reported. The shallow centers consist of a negatively charged Be substituting for a Si atom, ${\mathrm{Be}}_{\mathrm{Si}},$ with the main spin density, 30%, located in a dangling $p_z$ orbital on the nearest neighboring C. The deep centers consist of a ${\mathrm{Be}}_{\mathrm{Si}}$-C-vacancy pair, with the main spin density, 75–90 %, located on the three Si on the other side of the vacancy. In the as-grown Be-doped samples the EPR lines of the deep centers are either absent or much weaker than those in the Be diffusion sample. This can be understood by assuming that the diffusion of Be introduces more vacancies than in the as-grown sample, leading to a high concentration of deep centers.