Synthesis, integration and application of zinc oxide nanowires

Fast synthesis of ZnO nanowires via inductive heating in a room temperature chamber has been developed with two integration demonstrations: a self-assembled lateral integration via local vapor transport on micro fabricated chip and a vertical array integration via a post microfabrication process. These two integration approaches combine both bottom-up and top-down processes to construct ZnO nanowire-based devices for ultraviolet (UV) and chemical sensing applications.;ZnO nanowires with random and aligned orientations have been rapidly synthesized by means of inductive heating on silicon and 4H-SiC (0001) substrates, respectively. The total synthesis time can be less than 5 minutes, using ZnO/graphite as the solid source powder. Synthesized nanostructures under scanning electron microscopy show diameters of 20-120 nm with lengths up to 5 mum, and the single-crystalline lattice has been observed under transmission electron microscopy with growth direction along <0001>. Electrical properties of a synthesized ZnO nanowire have been characterized by connecting it in a field-effect transistor configuration.;The lateral integration of ZnO nanowires is developed based on the technique of on-chip local vapor transport. ZnO nanowires with average diameter of 50-60 nm have been connected between two suspended MEMS microstructures prepared by a silicon-on-insulator (SOI) process. These two-terminal, suspended ZnO nanowires are readily available for sensing applications, including UV light detection and gas sensing. UV sensing experiments have shown that the conductance of these wide-bandgap ZnO nanowires increases under UV illumination at 365 nm wavelength. Furthermore, UV-enhanced oxygen sensing has been achieved for photochemical application. The current-voltage (I-V) characteristics of the fabricated device show up to 500% improvement in oxygen sensitivity as compared with data without UV.;A low temperature and simple vertical integration process for ZnO nanowire arrays has been accomplished by constructing n-type ZnO nanowires/ p-type silicon heterojunction. This hybrid bottom-up and top-down process starts with the synthesis of ZnO nanowires using a thin layer of gold catalyst on top of a p-silicon substrate. This process allows direct vertical integration of high quality one dimensional (1D) structures using spin-on glass (SOG) as the isolation layer as well as the foundation for the top electrode. The I-V characteristics of the integrated system show typical rectifying behavior of heterojunctions. The photodiode exhibits response of ∼0.07 A/W under 365 nm UV light illumination with a 20 Volt reverse bias.