Ambient air effects on electrical transport properties of ZnO nanorod transistors

ZnO nanorod (NR) transistors were fabricated in a back-gated structure, and their electrical transport properties were investigated as a function of air pressure. A large shift (19.4 V) of threshold voltage (V _t,g) toward negative gate bias is observed as the air pressure decreases to 9.06 × 10 ^-4 Pa. The shift of V _t,g and the change in the flowing current between the source and drain electrode with changing the air pressure are fully reversible. The adsorption and desorption of oxygen molecules and/or OH groups in air are likely to be responsible for the reversibility. Most importantly, the electron concentration and the flowing current rapidly change only in a vacuum regime less than a certain pressure as likely as 1.33 × 10 ^-1 Pa. In contrast, in the low vacuum regime (>1.33 × 10 ^-1 Pa) ZnO NR transistors are insensitive to the change of air pressure. This observation indicates that nano-sized vacuum sensors based on ZnO NR transistors will be effective only in the high vacuum regime.