Influence of defect density states on NO2 gas sensing performance of Na: ZnO thin films

Abstract

In this work, the Zn1-xNaxO (x = 0, 0.01, 0.03, and 0.05) thin film gas sensors were prepared via the sol-gel spin coating method to study the impact of sodium on structural, morphological, elemental, electrical, and gas sensing applications. Crystal structure (XRD), energy dispersive X-ray analysis (EDX), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), four-probe hall measurement, and NO2 gas sensing properties were investigated to ascertain the elemental composition, morphology, defect density states, working temperature, response/recovery time, stability, selectivity, and repeatability. The 3 wt.%Na:ZnO gas sensor displays a gas-accessible structure with more oxygen vacancies, remarkable stability, and sensitivity towards NO2 gas at an optimum temperature (210 °C). A possible gas-sensing mechanism was also discussed and correlated with structural, elemental, morphological, and electrical properties.