Structural and photoelectrochemical properties of SrTaO2N oxynitride thin films deposited by reactive magnetron sputtering

In this study, the influence of the degree of crystallization and thickness of films was correlated with the photoelectrochemical performance of SrTaO2N semiconductor films for O2 evolution reaction under visible light irradiation. Oxynitride films were deposited on various substrates using the sputtering in Ar + N2 reactive atmosphere from a home-made SrTaO2N target. Films with stoichiometric composition were obtained at a high temperature (TS =800 °C) with reduced bandgap. The different substrates led to diverse degrees of film crystallization, from weakly crystallized to fully c-axis oriented. The photoelectrochemical performance was improved by improving the film crystallinity and the thickness. For further improvement of the photoelectrochemical performance, the following three limiting factors are identified: 1) low absorption coefficient, especially in the visible domain from 500 to 600 nm; 2) short lifetimes of excited charge carriers; and 3) permittivity with only moderate values lower than 10 in the visible-light domain.