Electron transport mechanisms in individual cobalt-doped ZnO nanorods

This study examined carrier transport in single cobalt-doped zinc oxide (Co:ZnO) nanorods in temperatures ranging from 80 to 405 K. Measurements were taken on single nanorods deposited on a Si template, where two- and four-point metallic contacts were previously made using e-beam lithography, dielectrophoresis, and focused ion beam. In both two- and four-point probe measurements, the current–voltage curves were clearly linear and symmetrical with respect to both axes. The electrical measurements were carried out according to three different measuring methods to accurately determine the resistivity of the single Co:ZnO nanorods. The Co-doped nanorods exhibited ferromagnetic behavior at room temperature. The remanence permanent magnet of the nanorods increased with increasing Co concentration, however, this was accompanied by the decrease in electrical resistivity. The transport properties were dominated by the thermal activation of electrons from the Fermi level to the conduction band for a temperature above 140–160 K, and to the impurity band at a lower temperature. The electronic transport of the nanorods was influenced by the surface states when exposed in the air.