Electronic and transport of unbalanced sublattice N-doping in Graphene

The incorporation of foreign atoms into the carbon honeycomb lattice has been widely investigated in order to modify the electronic and chemical properties of graphene [1,2]. Recent scanning tunneling microscopy and spectroscopy studies of nitrogen (N) doped graphene have revealed how the incorporation of this foreign atom into the sp2 lattice occurs. Joucken and coworkers showed that the exposure of graphene to a nitrogen plasma flux after synthesis leads to a homogeneous distribution of substitutional atoms [3]. However, when a nitrogen source is introduced during the CVD growth of graphene, the nitrogen incorporation can exhibit a preferential accommodation within one of the two triangular sublattice that compose the honeycomb lattice [4,5]. This wayward incorporation of nitrogen into graphene is not yet understood. Nevertheless, the consequences of such a peculiar single sublattice N-doping on the electronic and transport properties of graphene are addressed in this work. Electronic transport properties of N-doped graphene with a single sublattice preference are investigated using both first-principles techniques and a Kubo-Greenwood approach. Such a break of the sublattice symmetry leads to the appearance of a true band gap. A band gap opening due to an ordered superlattice of dopants has already been discussed [6,7]. However, such a periodic doping configuration is rather difficult to envisage experimentally. Here, we demonstrate the robustness of the band gap opening for the case of a random distribution of dopants in the same sublattice. In addition, a natural spatial separation of both types of charge carriers at the band edge is observed, leading to a highly asymmetric electronic transport. For such N-doped graphene systems, the carriers at the conduction band edge present outstanding transport properties with long mean free paths, high conductivities and mobilities. This phenomenon is explained by a quasi-ballistic regime which originates from the fact that corresponding electrons reside mainly in the unaltered sublattice yielding such low scattering rate. The presence of a true band gap along with asymmetric transport properties suggest the use of such N-doped graphene in GFET applications, where a high ION/IOFF ratio is needed. The present simulations appeal for more investigations on samples where such a peculiar N-doping has been observed. References [1] P. Ayala, R. Arenal, A. Loiseau, A. Rubio, and T. Pichler, Rev. Mod. Phys. 82 (2010) 1843. [2] M. Terrones, A. Filho, A. Rao. Doped Carbon Nanotubes: Synthesis, Characterization and Applications in Carbon Nanotubes Springer (2008) 531. [3] F. Joucken, Y. Tison, J. Lagoute, et al. Phys. Rev. B 85 (2012) 161408(R). [4] L. Zhao, R. He, K.T. Rim et al., Science 333 (2011) 999. [5] R. Lv, Q. Li, A.R. Botello-Mendez et al., Nature Scientific Reports 2 (2012) 586. [6] R. Martinazzo, S. Casolo, and G.F. Tantardini, Phys. Rev. B 81 (2010) 245420. [7] S. Casolo, R. Martinazzo, and G.F. Tantardini, J. Phys. Chem. C 115 (2011) 3250. [8] A. Lherbier, A. R. Botello-Méndez, J.-C. Charlier (submitted