Structural and Photoelectrochemical Properties of GaP Nanowires Annealed in NH3

Nitrogen alloyed gallium phosphide (GaP1–xNx) nanowires have been prepared by annealing gallium phosphide (GaP) nanowires in flowing NH3(g) at 750 °C. X-ray diffraction patterns and electron microscopy showed that changes in the annealing conditions afforded controlled alloying of N without effecting a complete conversion to gallium nitride (GaN). Raman measurements on nanowire films and individual nanowires highlighted intense new signatures, consistent with symmetry reduction from N incorporation in the zincblende lattice. The resultant optical properties and photoresponse of the GaP1–xNxnanowire films were investigated by wavelength-dependent diffuse reflectance and photoelectrochemical measurements, respectively. Diffuse reflectance measurements showed progressively lower reflectivity of visible light for nanowire films annealed in increasingly higher levels of NH3(g), indicating an increased light absorption. Corresponding photoelectrochemical measurements of the GaP1–xNxnanowires revealed an increased quantum efficiency, relative to GaP, for energy conversion of light with wavelengths longer than 545 nm. The presented data set thus identifies a methodology for improving the solar energy conversion properties of GaP nanowire film photoelectrodes for visible light.