Investigation of thickness effect on NO2 gas sensing properties of ZnO/Na thin films

Abstract

This present communication studies the dependences of film thickness, electrical properties, and film morphology on the gas detection capability of Na/ZnO thin films. The phase formation, microstructure, surface composition, and electrical parameters of these films were analyzed by XRD, FESEM-EDAX, and Hall measurement. XRD measurements reveal that the crystal quality of Na doped ZnO films is enhanced with the increase in the sensing layer thickness. The morphology of samples shows a transition of grain shape from spherical to irregular as the films become thicker. The film thickness shows variations in the range from 132 nm to 356 nm. Hall measurement concludes that Na doping concentration induces p-type conductivity in ZnO. The Na/ZnO film of a thickness of 132 nm emerged as the suitable NO2 sensor with better sensitivity and the fastest res/rec property. The obtained discrepancy in responsivity is attributed to the difference in grain size and carrier concentration with a change in film thickness.