Boron and nitrogen impurities in SiC nanowires

We have performed a theoretical ab initio study of the B and N impurities in hydrogen-passivated SiC nanowires (NWs). The calculations were performed within the density-functional theory, and using norm-conserving pseudopotentials to describe the electron-ion interactions. We have considered SiC nanowires growth along the [100] and [111] directions. For B-doped SiC NWs, our results indicate that the atomic relaxations around the impurity site play an important role to the energetic preference of B atoms occupying the Si sites $({\text{B}}_{\text{Si}})$ at the NW surface. The formation of ${\text{B}}_{\text{C}}$ becomes energetically more favorable than ${\text{B}}_{\text{Si}}$ only at the Si-rich condition. On the other hand, even at the Si-poor condition, the formation of ${\text{N}}_{\text{Si}}$ is not expected to occur, ${\text{N}}_{\text{C}}$ being the energetically more favorable configuration. In particular for the C-coated SiC NW growth along the [100] direction and the SiC NW growth along the [111] direction, the ${\text{N}}_{\text{C}}$ atoms are energetically more stable at the inner sites of the NWs. Thus, indicating that in those systems the ${\text{N}}_{\text{C}}$ atoms do not segregate toward the NW surface.