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

In this paper, we present an overview of the different shallow and deep acc eptor centers in Be-9-doped 6H-SiC. 95-GHz electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDO) measurements have been p erformed to determine their g, hyperfine, and quadrupole tensors and up to eight different centers were identified. The geometric and electronic struc ture of these centers resembles that of the B-related centers in 6H-SiC. Th ree of them showed the behavior characteristic of shallow B centers, five o f them that of deep centers. Three of the deep centers, that have their sym metry 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 degrees to the c axis a nd have not been found in B-doped 6H-SiC. To our knowledge this is the firs t time that deep Be acceptor centers are reported. The shallow centers cons ist of a negatively charged Be substituting for a Si atom, Be-Si, with the main spin density, 30%, located in a dangling p(z) orbital on the nearest n eighboring C. The deep centers consist of a Be-Si-C-vacancy pair, with the main spin density, 75-90 %, located on the three Si on the other side of th e vacancy. In the as-grown Be-doped samples the EPR lines of the deep cente rs 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. [S0163-1829(99)11647-3].