Transport properties ofWSe2nanotube heterojunctions: A first-principles study

Abstract

Using the nonequilibrium Green's function method within the framework of density functional theory, we investigate various transport properties, such as $I\ensuremath{-}V$ characteristics, shot noise, thermopower, dynamical conductance, of Au- and Na-encapsulated ${\text{WSe}}_{2}$ nanotube heterojunctions. First-principles transport calculations show that from $I\ensuremath{-}V$ curves large rectification ratio is found in the (8,0) heterojunction and for shot noise it exhibits sub-Poissonian behaviors under positive biases (on Au-encapsulated tubes) while Poissonian behaviors are found under negative biases. For thermopower, it is found that as one sweeps the Fermi energy, the thermopower can change its sign. For dynamic conductance, the (5,5) heterojunction exhibits capacitivelike behavior. We find that the spin-orbit interaction (SOI) is very important for ${\text{WSe}}_{2}$ nanotubes. Due to the band splitting originated from SOI, the intrinsic band gap of Au-doped (5,5) nanotube is reduced by about 58% and that of the Na-doped system vanishes, while that of the doped (8,0) nanotubes decreases by about 40%. The reduction of band gap has an important impact on the transport properties. For instance, the transmission gap is decreased by about 48% and 16% in the transmission spectrum of the (5,5) and (8,0) heterojunctions, respectively. The current of the (5,5) heterojunction under small bias is almost doubled and the rectification ratio of the (8,0) heterojunction is enhanced by more than 120% due to SOI.