Novel electronic and magnetic properties in N or B doped silicene nanoribbons

Motivated by experimental developments on silicene nanosheets, we performed first-principles calculations to study the geometric, electronic and magnetic properties of pristine, N or B doped, as well as N and B co-doped silicene nanoribbons (SiNRs). It is shown that the substitution of N or B for Si is preferentially at the ribbon edge sites. A singly substituted N or B atom at the edges results in a semiconductor-metal transition in armchair silicene nanoribbons (ASiNRs) because of the appearance of half-filled impurity band near the Fermi level. When the N/N or B/B atoms are doped into ASiNRs at two opposite edges, they preserve the metallic character due to a negligible impurity-impurity interaction, independent of the ribbon widths. However, the co-doped systems with N and B atoms exhibit semiconducting behavior with band gaps smaller than the corresponding pristine forms, due to effective charge compensation between N or B atoms. When Si is substituted by an N or B atom in zigzag silicene nanoribbons (ZSiNRs), the systems show ferromagnetic (FM) character, which is attributed to the perturbation of pi and pi* states localized at the doped edges. More importantly, the marvelous half-metal and spin gapless semiconductor with 100% spin polarized currents around the Fermi level has been found in N-doped ZSiNRs. Providing that the doping with two N/N or B/B atoms is made in ZSiNRs, the spin-polarization at both Si edges is found to be compressed, and thus they exhibit nonmagnetic behavior. However, when the N and B atoms are co-doped into ZSiNRs at the most stable edge positions, a transition from metallic to semiconducting state will appear. These predicted properties may lead to a new route for energy band engineering of SiNRs and benefit the design of silicene-based electronic devices in nanoelectronics.