Semiconducting WO3 thin films prepared by pulsed reactive magnetron sputtering

WO3 crystalline semiconductor thin films for water-splitting applications were prepared by pulsed unbalanced reactive magnetron sputtering with W target and Ar + O2 gas mixture. Postdeposition annealing at temperature of 450 °C was applied to the WO3 samples to improve their crystallinity and semiconductor properties. Various pulsing modes were tested in deposition experiments with different pulsing frequencies, discharge power applied in pulse, and average applied power. To determine the influence of the plasma parameters on the deposition process, the pulsed and average ion flux density on the substrate were measured using an ion probe. The WO3 films had monoclinic crystalline structure after the annealing process. Different crystallite orientations were found for different modes of discharge pulsing. Preferential orientation of the (200) plane parallel to the substrate surface was identified for higher frequency of discharge pulsing with lower substrate pulsed ion flux but higher average substrate ion flux. The WO3 films with this type of texture had the highest photocurrents in photoelectrochemical (PEC) measurements.