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 Vt, g toward negative gate bias is observed as the air pressure decreases to 9.06 × 10−4 Pa. The shift of Vt, 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 nanosized vacuum sensors based on ZnO NR transistors will be effective only in the high vacuum regime.