Optical and electrical properties of ZnO nanowires grown on aluminium foil by non-catalytic thermal evaporation

Well-crystallized ZnO nanowires were grown in large quantity on aluminium foil, by a non-catalytic thermal evaporation method using metallic zinc powder in the presence of oxygen at low temperature. Detailed structural and optical characterizations confirmed that the as-grown nanowires were highly crystalline, possessed a wurtzite hexagonal phase, had grown along the c-axis direction and exhibited excellent optical properties. The electrical characteristics of an individual nanowire were observed in air and vacuum by fabricating field-effect transistor (FET) devices. The transistors turned on typically between -5 and 0 V in ambient air. However, a large threshold voltage (Vth) shift, similar to 5 V, towards negative gate bias was observed in high vacuum. The shift of Vth is believed to be related to the charge transfer from the ZnO nanowire surface to the physically adsorbed OH or oxygen. Moreover, the fabricated FETs show a high conductivity ON/OFF ratio of about similar to 10(2) with ultraviolet (UV) light and hence provide an effective way to use these devices in nanoscale UV detectors and optoelectronic switches.