Growth of high quality ZnO:Mg films on ITO coated glass substrates for enhanced H2 sensing

Magnesium doped Zinc oxide (ZnO:Mg) thin films were prepared on ITO coated glass substrates by spray pyrolysis method. The effect of Mg dopant concentration on the structural, morphological and optical properties of ZnO thin films was investigated. X-ray diffraction studies showed that the ZnO:Mg films have polycrystalline hexagonal wurtzite ZnO structure. The compressive stress in ZnO:Mg turns into tensile stress at higher Mg dopant concentration due to the improvement in the crystal quality of the film. The most important changes were observed for the films doped with 3% Mg, which exhibit a transmittance of ~90%. The blueshift in the UV emission peak of ZnO:Mg with increasing Mg content, and increase in band gap upto 3% Mg suggest the tunable band gap of ZnO by Mg. The surface morphology of ZnO:Mg shows few hexagonal and spherical shaped grains distributed randomly over the surface of ITO substrate. The development of flowery arrangement of grains inside a closed ring shows the effect of the microstructure of ITO underlayer. The hydrogen sensing characteristics of ZnO:Mg films were investigated and the resistance of the sensor was measured for different concentration of H2 gas. The results reveal a high reactivity efficiency to H2 for high Mg dopant concentration of 3%, due to the high surface activity for smaller ZnO particles on ITO lattice.