Oxygen sensing characteristics of individual ZnO nanowire transistors

Individual ZnO nanowire transistors are fabricated, and their sensing properties are investigated. The transistors show a carrier density of $2300\mu {\mathrm{m}}^{-1}$ and mobility up to $6.4{\mathrm{cm}}^2∕\mathrm{V}\mathrm{s}$ , which are obtained from the $I_{\mathit{SD}}-V_G$ curves. The threshold voltage shifts in the positive direction and the source-drain current decreases as ambient oxygen concentration increases. However, the opposite occurs when the transistors are under illumination. Surface adsorbates on the ZnO nanowires affect both the mobility and the carrier density. Our data are helpful in understanding the sensing mechanism of the gas sensors.