Photoelectrochemical properties of nitrogen-doped indium tin oxide thin films prepared by reactive DC magnetron sputtering

Nitrogen-doped indium tin oxide (N-ITO) thin films are deposited on unheated ITO glass substrates in this study. The structural properties of the N-ITO thin films, determined by X-ray diffraction (XRD) and Raman scattering, show that the indium nitride (InN) phase is liable to form in N-ITO films prepared in 20% N2. A broad XRD peak around 2θ=33° and Raman peak around 490cm−1 are assigned to the InN phase, but no such peak is observed from the ITO film. Hence, the bandgap is narrowed by N-doping for absorbing light of longer wavelengths of ~500nm. However, under illumination by ultraviolet, the N-ITO film prepared in 20% N2 exhibits the least photocurrent response, which is less than one third that of the N-ITO catalyst that was doped in 16.4% N2. This result is attributed mostly to the fact that the valence and conduction band potentials are not positioned properly between the newly formed InN and host ITO phases, rendering inefficient inter-semiconductor electron transfer. Therefore, higher N-doped samples exhibit a lower photocurrent response. Interestingly, the N-ITO film prepared in 16.4% N2 exhibits the highest photocurrent density of about 165.5μA/cm2 at an applied bias of 1.2V. This implies that the N-ITO films should be prepared at a low N2 ratio to ensure a favorable photoelectrochemical activity.