Low resistive gallium doped nanocrystalline zinc oxide for gas sensor application via sol–gel process

Abstract

This paper reports the effect of low concentration of Ga doping on the performance of ZnO thin-film based gas sensors. The ZnO films were synthesized on the alkali-free glass substrates by employing a sol–gel process. Different concentrations of Ga were added to the sol–gel mixture for systematic comparison of doping effect. The effect of Ga doping on the microstructure, optical properties, surface morphology, electrical conductivity and gas sensing characteristics was investigated comparing undoped and Ga-doped ZnO thin films. The results revealed that the grain size decreased after the doping of Ga in ZnO. The optical transmittance and bandgap of ZnO films were not affected by the doping of Ga. The Ga doping resulted in a significant increase in electrical conductivity of ZnO thin films. The gas sensing behavior was studied under different concentrations of H2 exposure in the air at an operating temperature of 130°C. The results indicated that the sensing response for H2 was enhanced after the doping of a trace amount of Ga. It was found that 0.3at.% was the optimum Ga doping concentration for ZnO sensors in the low Ga doping concentrations, which exhibited both high response and short response time. The selectivity of 0.3at.% Ga-doped ZnO sensor was investigated for important industrial gas mixtures. It was found that the Ga-doped ZnO sensors exhibited a better detection capability of H2 than NH3 and CH4.