Development of NiO-based thin film structures as efficient H2 gas sensors operating at room temperatures

P-type NiO thin films have been developed on high resistivity Si and SiO2 substrates by a pulsed laser deposition technique using an ArF* 193 nm excimer laser at deposition temperature of 300 degrees C and in 40 Pa partial oxygen pressure. Structures based on such NiO films as host material in the form of Au-NiO Schottky diodes have been subsequently developed under vacuum. In a different procedure, an n-SnO2 layer has been deposited by a CVD technique on a NiO film to produce a p/n heterojunction. The sensing properties of all above structures have been tested upon exposure to a H-2 flow in air ambient gas at various operating temperature ranging from 30 to 180 degrees C. For the NiO films, the optimum temperature was about 150 degrees C exhibiting a sensitivity of 94%. After surface sensitization of NiO by An the NiO films showed an H, response at operating temperature of 30 degrees C. The sensitivity of p-NiO/n-SnO2 heterojunction devices was extracted from I-V measurements in air and under H-2 flow mixed in air. In this case a dramatic increase of the sensitivity was achieved at operating temperature of 30 degrees C for a forward bias of 0,2 V. (c) 2007 Elsevier B.V. All rights reserved.