Electronic structure of the shallow boron acceptor in 6H-SiC: A pulsed EPR/ENDOR study at 95 GHz

A high-frequency pulsed electron paramagnetic resonance electron-nuclear double-resonance (ENDOR) study on a C-13-enriched 6H-SiC single crystal is reported. This type of spectroscopy, owing to its superior spectral resolution, allows us to obtain detailed information about the electronic structure of the shallow boron acceptor centers in 6H-SiC. It is concluded that around 40% of the spin density is localized in the p(z) orbital of a carbon which is nearest to boron. The p(z) orbital is directed along the C-B connection line and is parallel to the c axis for the hexagonal site and 70 degrees away from the c axis for the two quasicubic sites. We conclude that the C-B bond is a dangling bond, that boron is neutral, and that there is no direct spin density on boron. There is a relaxation of the carbon atom, carrying the spin density, and the boron atom away from each other. From a Si-29 and C-13 ENDOR study it is further concluded that around 60% of the spin density is distributed in the crystal with a Bohr radius of 2.2 Angstrom.