Observation of Photoconductivity in Sn-Doped ZnO Nanowires and Their Photoenhanced Field Emission Behavior

Sn-doped ZnO nanowire films have been successfully synthesized by electrodeposition on zinc foil followed by annealing in air at 400 °C for 4 h. The XRD patterns of the annealed specimens exhibit a set of well-defined diffraction peaks indexed to the wurtzite phase of ZnO. The surface morphology of the as-synthesized films showed a network of densely packed flakes/sheets on the substrate. However, upon annealing, the formation of ZnO nanowires, processing length in the range of several micrometers and diameter less than 150 nm, on the entire substrate is observed. The relative atomic percentage of Sn, estimated from the energy dispersive spectra, was found to be 0.5 and 2.0 in the ZnO films deposited for 10 and 40 min durations, respectively. From the field emission studies, the values of the turn-on field and threshold field, required to draw emission current density of 10 and 100 μA/cm<sup>2</sup>, are observed to be 0.68 and 1.1 V/μm for 0.5% Sn-doped ZnO and 1.72 and 2.25 V/μm for 2.0% Sn-doped ZnO, respectively. The field emission current stability investigated for a duration of 6 h at the preset value of 100 μA is found to be excellent. A prominent photoenhancement in the field emission current upon visible light illumination of the Sn-doped ZnO nanowires films has been observed. This enhancement has been attributed to the photoconductivity of the Sn-doped ZnO.