Nitrogen dioxide induced conductivity switching in ZnO thin film

Abstract The spin coated ZnO thin films were synthesized and tested for O 2 and NO 2 gas detection. It exhibited an increase in resistance i.e. n-type behavior for O 2 exposure (5–20%) and decrease in resistance i.e. p-type behavior for NO 2 (2–40 ppm) exposure at operating temperatures of 250 °C and 300 °C in N 2 atmosphere (0.4 ± 0.03 mbar). The origin of this aberrant behavior for NO 2 exposure was attributed to the participation of defects in NO 2 sensing characteristics in light of the data obtained from photoluminescence and Raman spectroscopy studies demonstrating the unique defect morphology of ZnO thin film. The underlying mechanism is discussed on the basis of conclusions drawn from characterization techniques and subsisting knowledge in the literature. The NO 2 gas sensing is explained in terms of two competing mechanisms: one is change in charge carrier density on gas exposure as explained by surface depletion model and another is due participation of defects (oxygen vacancies) in gas sensing characteristics.