Photocurrent in ZnO nanowires grown from Au electrodes

ZnO nanowires were grown between two Au electrodes on an ${\mathrm{Al}}_2{\mathrm{O}}_3$ -deposited Si wafer. Photoresponse, photoresponse spectrum, and current–voltage $\mathrm{(I–V)}$ studies were performed for the investigation into photoconduction mechanism in these nanowires. The photoresponse of the nanowires under the continuous illumination of light with above- or below-gap energies was slow, which indicates that photocurrent in the nanowires is surface-related rather than bulk-related. The photoresponse spectrum represents the above- and below-gap absorption bands for the photocurrents. The $\mathrm{I–V}$ characteristics under the illumination of the above-gap light are ohmic, but the characteristics under the illumination of the below-gap light are Schottky. This observation indicates that the above-gap light lowers the potential barrier built in the contact between the ZnO nanowires and electrodes, but that the below-gap light does not lower the potential barrier.