Ethanol Sensing Characteristics of Nitrogen Doped ZnO and in2O3 Thin Films

Abstract

Gas sensing characteristics of semiconducting metal oxides (SMOs) are often modulated by incorporation of suitable dopants that influences oxygen vacancy formation, bang gap and crystal structure of SMOs. Impact of dopant incorporation at the cation site in diverse SMOs has been extensively investigated, whereas the anion site doping is less explored. In this work we report the impact of anion site substitution on the VOC sensing characteristics of SMOs. As a case study ethanol sensing characteristic of nitrogen doped ZnO and In2O3 thin films have been compared. The films were synthesized using spin coating of corresponding sols. Pure ZnO and In2O3 thin films were also synthesized as control samples. The structural and morphological features have been analyzed using XRD and SEM respectively. Presence of nitrogen in the thin films has been confirmed using XPS. The nitrogen substituted sensors exhibited enhanced sensing response towards ethanol in comparison to the pristine oxide films. Nitrogen substituted ZnO film exhibited highest response of 99.6 % at 225 °C, whereas the nitrogen incorporated In2O3 film exhibited a highest response of 99.5 % at 250 °C. Both the samples have shown fast response time of one second up to 200 °C and exhibited excellent long-term stability in their response. Further, nitrogen substituted ZnO has shown better selectivity towards ethanol compared to doped In2O3 thin film. Figure 1