GaN nanowires grown by halide chemical vapour deposition as photoanodes for photo-electrochemical water oxidation reactions

Abstract

Manifold morphologies of GaN nanowires (NWs) were fabricated using halide chemical vapour deposition (HCVD) on an n-Si (111) substrate and demonstrated to be a promising photoelectrode for photo-electrochemical (PEC) water splitting applications. We report a substantial enhancement in the photocurrent for vertically-grown GaN NWs on a buffer layer as compared to other counterparts such as GaN whiskers, tapered nanostructures and thin films. GaN NWs grown on Si have advantages due to the absorption of photons in a wide spectral range from ultraviolet to infrared and thus are directly involved in PEC reactions. A GaN NW photoanode was demonstrated with a saturation photocurrent density of 0.55 mA cm−2 under 1 sun of illumination, which is much greater than its counterparts. The role of the buffer layer and the carrier density on the PEC performance of vertically-grown GaN NW photoanodes is further elucidated. Photo-electrochemical impedance spectroscopy and Mott-Schottky characterizations were employed to further explain the PEC performance of GaN NW embedded photoanodes. Here, photoanodes based on diverse GaN nanostructures were examined for a better PEC evaluation in order to support the conclusion. The results may pave the way for the fabrication of efficient photoelectrodes and GaN as a protective layer against corrosion for improved photo-stability in an NaOH electrolyte for enhancing the efficiency of water splitting.