Electrical Transport Study of Single-Walled ZnO Nanotubes: A First-Principles Study of the Length Dependence

The electronic transport properties are characterized for single-walled zigzag (9, 0) ZnO nanotubes sandwiched between two lithium electrodes using a combined nonequilibrium Green’s function and DFT-based formalism. By applying different bias voltages, the current−voltage characteristics are calculated for nanotubes of different lengths. The results indicate that the conductance of the system decreases exponentially with the increased length of the nanotubes. Metallic behavior is predicted for very short nanotubes, which is caused by the interface states from the metal−nanotubes interface. For longer nanotubes, the effect of the interface becomes smaller with the increased lengths. And semiconductor-like behaviors are observed, which are mainly determined by the ZnO nanotubes themselves. In addition, a peculiar phenomenon is observed that the values of the current at high bias are insensitive to the lengths. The behaviors can be understood in terms of the transmission spectrum, which shows that the transport properties are dominated by the electron states above the Fermi energy.