Effect of surface states on electron transport in individual ZnO nanowires

The current–voltage (I–V$I\text{–}V$) characteristics of single ZnO nanowires have been studied in the humid air, dry air, vacuum, and under ultraviolet (UV) irradiation. A model of a single ZnO nanowire connected with two opposite diodes was proposed to calculate the observed I–V$I\text{–}V$ behaviors. The results show that the electrical characteristics are dominated by the reverse barrier height, and the barrier height can be adjusted by surface adsorption, which is ascribed to the effect of surface states on surface band bending and Fermi level pining. Furthermore, the nanowire exhibited an enormous increase of conductance upon UV irradiation and a considerable persistent photocurrent after withdraw of the UV excitation, which further confirms the surface states have a pronounced effect on the electronic transport in single ZnO nanowires.