  Using ab initio calculations based on density-functional theory we have
performed a theoretical investigation of substitutional boron and nitrogen
impurities in silicon carbide (SiC) nanoribbons. We have considered hydrogen
terminated SiC ribbons with zigzag and armchair edges. In both systems we
verify that the boron and nitrogen atoms energetically prefer to be localized
at the edges of the nanoribbons. However, while boron preferentially
substitutes a silicon atom, nitrogen prefers to occupy a carbon site. In
addition, our electronic-structure calculations indicate that (i)
substitutional boron and nitrogen impurities do not affect the semiconducting
character of the armchair SiC nanoribbons, and (ii) the half-metallic behavior
of the zigzag nanoribbons is maintained in the presence of substitutional boron
impurities. In contrast, nitrogen atoms occupying edge carbon sites transform
half-metallic zigzag nanoribbons into metallic systems.
