Investigation of sol-gel prepared Ga-Zn oxide thin films for oxygen gas sensing

Gallium oxide-zinc oxide (Ga2O3-ZnO) thin films have been prepared by the sol-gel process and their oxygen gas sensing performance has been investigated. These semiconducting films were deposited on alumina substrates with interdigital electrodes and single crystal silicon substrates for the electrical and microstructural characterization. X-ray photoelectron spectroscopy (XPS) showed that the actual concentrations of Ga and Zn thin films differ from the nominal values in the prepared solutions. Additionally, the concentration of ZnO decreases when the annealing temperature increases. Scanning electron microscopy (SEM) revealed that films with Ga/Zn atomic ratio 90:10 possess cracks and are inhomogeneous when compared to those with that of 50:50. The sensors with Zn 50 at.% had a much larger response at lower operating temperature (<430 °C) compared to the Ga-dominated sensors, which operate above 450 °C. Furthermore, these sensors showed greatest performance at temperatures in the range of 380-420 °C. It was found that by increasing the amount of ZnO in the thin film sensors, the operating temperature decreased as well as the base resistance.