Ab initio study of nitrogen and boron substitutional impurities in single-wall SiC nanotubes

Silicon carbide nanotubes have a great potential for application in chemical sensors in harsh environment or in biological sensors. It is of interest to explore the electronic properties of these nanotubes, and how those are modified in the presence of impurities. It is well known that nitrogen and boron atoms are common contaminations in bulk silicon carbide (SiC). Nitrogen preferentially substitutes the carbon site making n-type conductivity in bulk SiC. Boron substitutes both carbon and silicon sites forming a deep and a shallow acceptor in bulk SiC, respectively. In this paper we have studied these defects in armchair and zig-zag SiC nanotubes by ab initio supercell calculations. We found that nitrogen forms relatively shallow or deep donor state depending on the width of the band gap of the SiC nanotube. Boron is a relatively deep or shallow acceptor at carbon and silicon sites, respectively, like in bulk SiC polytypes. The site preference of boron depends on the stoichiometry of the SiC nanotubes. We have found no significant difference in the properties of boron substitutional defect between armchair and zig-zag nanotubes.