Contact to ZnO and intrinsic resistances of individual ZnO nanowires with a circular cross section

Single crystalline ZnO nanowires (NWs) with a circular cross section and $∼40nm$ in diameter have been synthesized and utilized to fabricate two-contact ZnO NW devices. The electrical properties of the NW devices can be categorized into two classes according to the magnitude of their room-temperature resistances. $I-V$ curves of low-resistance devices exhibit downward bending features and their temperature dependent resistances demonstrate thermal activation transport in the ZnO NWs. The high-resistance NW devices can be modeled as back-to-back Schottky contacts and the electron transport through the contacts reveals a variable-range-hopping mechanism.