Electronic and transport properties of graphene nanoribbons

We present the electronic structures and transport properties of hydrogen-saturated graphene ribbons and its dependence on its termination edge, ribbon width, and impurity. The band structures, transmission spectrum, and current-voltage (I-V) characteristics of graphene ribbons have been calculated by using first-principles electronic structure methods and non-equilibrium Green´s functions technique. Our calculated results show that the graphene ribbons with zigzag shaped edges exhibit nonlinear behavior of I-V characteristics due to the overlapping of pi* and pi bands around Fermi level. As the width of zigzag chain of graphene ribbons increases, the overlapping of pi* and pi bands is enhanced and the voltage range for linear I-V response becomes narrower. The graphene ribbons with armchair shaped edges exhibit semiconducting properties and the band gap decreases with increasing ribbon width. The doping of B or N in graphene ribbons with armchair shaped edges slightly increases the current at lower bias voltage.