Rectifying and NO Gas Sensing Properties of an Oxide Heterostructure with ZnO Nanorods Embedded in CuO Thin Film

A novel oxide p–n heterojunction structure with n-type ZnO nanorods embedded in p-type CuO thin film was fabricated on an indium tin oxide-coated glass substrate by combining a hydrothermal synthesis method and a sputtering deposition method. The transport behavior and NO gas sensing properties of the p-CuO thin film/n-ZnO nanorods heterostructure were characterized. The oxide heterojunction structure exhibited a definite rectifying diode-like behavior at various temperatures ranging from room temperature to 250 °C. Forward current–voltage (I–V) data revealed that the conduction under high forward bias becomes space-charge-limited and follows I ≈ V ^1.9. When the oxide p–n heterojunction structure was exposed to the acceptor gas NO in dry air, an abrupt decrease in the forward diode current of the p–n junction was observed. The NO gas sensing response of the oxide heterojunction structure showed a maximum value at a comparatively low operating temperature of 180 °C and increased linearly with increasing NO gas concentration in the range of 5–30 ppm. Results indicate that the p-CuO thin film/n-ZnO nanorods heterostructure has significant potential applications for oxide electronics, including gas sensors.