Gas molecular adsorption and surface cleansing effects on the electrical properties in ZnO nanowire field effect transistors

We fabricated field effect transistors by using high quality single-crystalline ZnO nanowires and studied their electrical properties by gas adsorption. We measured the changes in the electrical properties due to the surface absorbed OH or O-2 from the ambient air. A rapid change in the threshold voltage of the gate response curve in the high vacuum region has been reproducibly observed. This change suggests that the adsorption mechanism may he different in the low and the high vacuum regions. By introducing reactive gas molecules to the surface of the nanowire channel in the high vacuum condition via a mass flow controller, we could tune the number of carriers. We then obtained optimally-doped devices from the heavily-doped ones. We also developed an effective surface cleansing procedure to enrich the electrical properties of pristine devices significantly by the introducing high-purity O-2 gas under high vacuum conditions.