H2S gas sensitive indium-doped ZnO thin films: Preparation and characterization

High quality indium-doped ZnO (IZO) thin films (∼100 nm) have been deposited onto the glass substrates by using a conventional spray pyrolysis technique. Precursors such as zinc acetate, indium chloride with Brij-35 (polyoxyethylene lauryl ether) as a non-ionic surfactant were used. The morphology, crystal structure, elemental analysis and the gas response properties were investigated by using SEM, TEM, XRD, AFM and XPS techniques. The films show hexagonal wurtzite structure which reveal variations in (1 0 0), (0 0 2) and (1 0 1) intensities with indium doping. The crystallite size calculated by Scherrer formula was in the range of 30–50 nm. The SEM and AFM analysis show 50–70 nm sized grains, while the TEM confirms formation of grains by ∼10 nm sized particles. Their response towards various gases was measured at different operating temperatures and different levels of In-dopants. The 3 at% In-doped ZnO showed response as high as 13,000 for 1000 ppm H2S at 250 °C. It exhibited fast response (∼2 s) and recovery time (∼4 min). The gas response strongly depends on the morphology and indium concentration. The high gas response of IZO is explained on the basis of thickness dependent trap state density.