Positive and Negative Photoconductivity Conversion Induced by H2O Molecule Adsorption in WO3 Nanowire.

Negative photoconductivity effect has been observed in the Au/WO3 nanowire/Au devices in a high humidity environment, which might be attributed to the accumulation of H+ ions on the surface of WO3 nanowire. Under illumination with violet light (445 nm), the photo-excited holes can oxidize the adsorbed H2O molecules to produce H+ ions and O2, while the photo-excited electrons at the conduction band bottom do not have enough energy to reduce H+ ions. These H+ ions will accumulate on the surface of the hexagonalWO3 nanowire. They will capture mobile electrons and then reduce the concentration of carriers, which will result in a significant increase in the height of interface barrier and then a significant decrease in the conductance of the Au/h-WO3 nanowire/Au device. By adjusting the relative humidity, light intensity, or bias voltage, the concentration and distribution of H+ ions and then the conversion between positive and negative photoconductivity, as well as resistive switching properties, can be well regulated in this kind of devices.