Using the non-equilibrium Green's functions formalism in a tight binding model, the spindependent transport in armchair graphene nanoribbon (GNR) structures controlled by a ferromagnetic gate is investigated. Beyond the oscillatory behavior of conductance and spin polarization with respect to the barrier height, which can be tuned by the gate voltage, we especially analyze the effect of width-dependent band gap and the nature of contacts. The oscillation of spin polarization in the GNRs with a large band gap is strong in comparison with 2D-graphene structures. Very high spin polarization (close to 100%) is observed in normal-conductor/graphene/normal-conductor junctions. Moreover, we find that the difference of electronic structure between normal conductor and graphene generates confined states in the device which have a strong influence on the transport quantities. It suggests that the device should be carefully designed to obtain high controllability of spin current.

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The fully self-consistent non-equilibrium Green functions (NEGFs) approach to the quantum transport is developed for the investigation of one-dimensional nano-scale devices. Numerical calculations performed for resonant tunneling diodes (RTDs) of different designs and at different temperatures show reasonable results for the potential and electron density profiles, as well as for the transmission coefficient and the current-voltage characteristics. The resonant behavior is discussed in detail with respect to the quantum-well width, the barrier thickness, and the temperature. It is also shown that within the framework of approach used the current noise spectral density can be straightforwardly calculated for both the coherent and the sequential tunneling models. In qualitative agreement with experiments, obtained results highlight the role of charge interaction which causes a fluctuation of density of states in the well and therefore a noise enhancement in the negative differential conductance region.

Motivated by recent studies on the use of graphene for new concepts of electronic/spintronic devices, the authors develop an efficient calculation method based on the nonequilibrium Green’s function to solve the quantum relativisticlike Dirac’s equation that governs the low-energy excited states in graphene. The approach is then applied to investigate the electronic transport and the spin polarization in a single-graphene barrier structure. The obtained results are presented and analyzed in detail aiming to highlight typical properties of the considered graphene structure as well as the efficiency of the developed approach that both may be helpful for further development in electronic devices and in spintronics.