Current-voltage characteristics of carbon nanotubes with substitutional nitrogen

We report ab initio analysis of current-voltage $(I-V)$ characteristics of carbon nanotubes with nitrogen substitution doping. For zigzag semiconducting tubes, doping with a single N impurity increases current flow and, for small radii tubes, narrows the current gap. Doping a N impurity per nanotube unit cell generates a metallic transport behavior. Nonlinear $I-V$ characteristics set in at high bias and a negative differential resistance region is observed for the doped tubes. These behaviors can be well understood from the alignment/mis-alignment of the current carrying bands in the nanotube leads due to the applied bias voltage. For a armchair metallic nanotube, a reduction of current is observed with substitutional doping due to elastic backscattering by the impurity.