CuO-doped WO3 thin film H2S sensors

•Growth of CuO-doped WO3 films by e-beam evaporation for application as H2S sensors.•Determination of thickness and refractive indices using interference fringes in transmittance and reflectance spectra.•Large increase in surface resistivity of WO3 on doping with CuO.•High H2S response with switching like response and recovery characteristics of CuO-doped WO3 film.•High H2S signal due to sulfurization of WO3 and CuO and destruction of p-n junctions. WO3 and CuO-doped WO3 (0.03CuO-0.97WO3) thin films were prepared by electron beam evaporation on fused silica and alumina substrates and their optical and H2S sensing properties were studied. As-deposited films were amorphous and crystallized into the monoclinic WO3 phase after annealing at 400 °C for 2 h in air. The thicknesses of the WO3 and CuO-doped WO3 films were 830 ± 10 nm and 642 ± 10 nm, respectively. The refractive indices were in the range: 2.33−1.80 in UV–vis-NIR region. The surface electrical conductivity of WO3 decreased drastically by ∼103 times on doping with 3 mol% of CuO. The H2S response of films was measured as a function of operating temperatures in the range of 200 °C–300 °C and it is found that CuO doping produces a large enhancement in H2S response. The sample 0.03CuO-0.97WO3 shows peak response of 11,700 for 600 ppm H2S at 275 °C. The response and recovery transients improve significantly with CuO doping in WO3 and with an increase in the sensor operating temperature from 200 °C–300 °C.