First-principles investigation on stability and diffusion mechanism of helium impurities in 4H-SiC

The stability, structure, energetics and diffusive properties of He impurities in 4H-SiC have been investigated by first principles calculations in order to understand its irradiation effects. The formation energies indicate a He atom is preferable to occupy the Si pre-existing vacancy at first. In turn, by formation of He defects associating at interstitial and vacancy sites require positive but low formation energies, suggesting its propensity diffusion in the material. By calculating its energy barriers corresponding to both the interstitial diffusion and vacancy assisted diffusion, we suggest that the most probable diffusion pathway involves the exchange of interstitial and vacancy positions with the effective migration energies from 0.1 eV to 1.0 eV. Remarkable, our calculated diffusion barriers are consistent well with previous theoretical data for He diffusion in 3C-SiC.