Facile fabrication of ZnO nanowire-based UV sensors by focused ion beam micromachining and thermal oxidation

ZnO nanowire UV sensors were fabricated by using focused ion beam micromachining and thermal oxidation of metallic zinc microstructures. A metallic zinc "micro-strip" was first deposited by thermal evaporation with the aid of a shadow mask on SiO2/Si substrate. A 3-μm wide "trench" was cut across the metallic strip by focused ion beam; the subsequent thermal oxidation at 450 °C results in the growth of single crystalline [110] ZnO nanowires across the trench. The ZnO nanowire sensor was completed by patterning silver ohmic contacts on the two ends of the metallic strip. Our photoluminescence (PL) spectroscopic studies show that the room temperature emission of the ZnO nanowire is due to the recombination of free exciton and free to bound transition, while at 10 K, the PL is dominated by the recombination of surface excitons. Irradiated at 300 nm, the rise time, decay time and normalized photoconductive gain of the ZnO sensor were determined to be 200 ms, 400 ms and 3 × 10−6 m2V−1, respectively. The fast sensor response is due to the high crystalline quality of the nanowire, which facilitates a rapid equilibrium of absorption and desorption of molecular oxygen on the surface.