Characterization of n-type and p-type semiconductor gas sensors based on NiOx doped TiO2 thin films

This work presents the development of n-type and p-type gas-sensitive materials from NiOx doped TiO2 thin films prepared by ion-assisted electron-beam evaporation. TiO2 gas-sensing layers have been deposited over a wide range of NiOx content (0-10 wt.%). The material analysis by atomic force microscopy, X-ray photoemission spectroscopy, and X-ray diffraction suggests that NiOx doping does not significantly affect surface morphology and Ni element may be a substitutional dopant of the TiO2 host material. Electrical characterization shows that NiOx content as high as 10% wt. is needed to invert the n-type conductivity of TiO2 into p-type conductivity. There are notable gas-sensing response differences between n-type and p-type NiOx doped TiO2 thin film. The responses toward all tested reducing gases tend to increase with operating temperature for the n-type TiO2 films while the response decreases with temperature for p-type TiO2 film. In addition, the p-type NiOx doping results in the significant response enhancement toward tested reducing gases such as acetone and ethanol at low operating temperature of 300 degrees C. (C) 2008 Elsevier B.V. All rights reserved.