Hydrogen sensing by ZnO/SiC based solid state structures

The hydrogen gas sensing performance of Pt/ZnO/SiC solid-state structures has been investigated. The ZnO thin films were deposited by a planar r.f. magnetron sputterer onto n-type 6H silicon carbide wafers. These devices were employed as Schottky diodes and operated in constant current mode. Exposure to different concentrations of hydrogen gas results in changes in the device's carrier concentration and hence in the Schottky barrier height. This results in a change in the forward bias voltage. The ZnO thin films, after annealing in static air at 300, 500, 700 and 900°C, have been characterized by X-ray Photoelectron Spectroscopy (XPS) and X-Ray Diffraction (XRD). The formation of hexagonal ZnO ICSD card. N° 29272 was observed when the films were annealed at temperatures greater than 500°C. The sensors responses to hydrogen were analyzed when the ambient gas was 5% oxygen balanced in nitrogen. These responses were stable and repeatable in the investigated temperature range of 300 and 500°C.