Temperature-dependent p-n switching for highly selective CO gas sensing based on mixed phases of magnetron sputtered (p)SnO-(n)SnO2 thin films

Abstract

We report on the deposition of mixed phases (p)SnO-(n)SnO2 thin films on Si substrate using reactive magnetron sputtering for CO gas sensing. The presence of mixed phases was observed in the XRD, and XPS results, and the p-type behaviour at room temperature was confirmed through Hall effects measurements. The other physical properties of the samples were studied by FESEM, Raman, UV–visible, and PL. We performed gas sensing measurements of (p)SnO-(n)SnO2 sample. Further, the optimum temperature for p-type nature was 150 °C, while for n-type nature it was 325 °C. The sample with p-type nature started responding even at low temperature (50 °C) for 100 ppm CO gas with ∼ 17 % of sensor response and reached a maximum value of sensor response of ∼ 96 % at 150 °C with a good response/recovery time of ∼ 116 s/158 s. While n-type nature displays a maximum sensor response value of ∼ 93 % at 325 °C with a faster response/recovery time of ∼ 24 s/80 s. The sample exhibited sensor response of ∼ 5 % and ∼ 8 % at 150 °C and 325 °C, respectively, for 500 ppb CO gas concentration. Thus, we observed the temperature-dependent switching from p-type to n-type of (p)SnO-(n)SnO2 films with high selectivity and stability towards CO gas.