Low-temperature epitaxial growth of high-quality GaON films on ZnO nanowires for superior photoelectrochemical water splitting

Gallium oxynitride (GaON) is an emerging material suitable as a key component to build efficient hetero-structures for photoelectrochemical (PEC) water splitting. However, the great difficulty in controlled growth of GaON films limits their applications. This study developed a novel method for depositing highly uniform GaON films by a one-step co-deposition process via plasma-enhanced atomic layer deposition (ALD). Importantly, this material presents high-quality epitaxial growth behavior on ZnO nanowires (NWs) only at 200 degrees C to construct ZnO-GaON core-shell NWs with different shell thickness (5-60 nm). Benefiting from the precisely controlled ALD technique, thickness-dependent PEC performance and its mechanism were studied deeply. It was found the ZnO-GaON NWs with an optimum shell thickness (similar to 40 nm) presented largest electric field enhancement and light-trapping ability, thus greatly improved the photocurrent from similar to 0.24 (pristine ZnO) to 2.25 mA/cm(2) at 1.23 V versus reversible hydrogen electrode. Meanwhile, this structure presents an ultrahigh incident photon-to-current conversion efficiency of similar to 90% in the UV region. A comparative study assesses the ultrahigh carrier density (similar to 10(21) cm(-3)) and suitable bandgap of GaON relative to GaN and Ga2O3, revealing a higher photocurrent for the ZnO-GaON core-shell NWs. These encouraging results indicated that higher PEC performance is worthy expected upon optimization of the nitrogen and oxygen concentrations and by combining with narrow bandgap materials in further studies.