GaN nanowire arrays for photocatalytic applications II: influence of a dielectric shell and liquid environments

GaN nanowires (NWs) are promising candidates for photocatalytic devices due to their large surface-to-volume ratio and their waveguide character. Protective coatings and nanoparticle co-catalysts are widely used to improve the stability and the photocatalytic activity of semiconductors in liquid electrolytes. Here, we present a systematic experimental study of the influence of a dielectric shell and liquid environments on the interaction of light with GaN NW arrays related to photocatalytic applications. Transmission measurements on bare GaN NWs and core–shell NWs with varying shell thickness and refractive index of the shell reveal a shift of the transmission minima that originate from the coupling of light to various waveguide modes supported within the NWs. This shift is a result of the shift of the dispersion relations of the modes for core–shell NWs. The transmission spectra of GaN NWs in liquid environments show a spatial and spectral shift. These results are explained by the dependence of both, the waveguide properties of the single NWs and the photonic crystal characteristics of the NW array, on the refractive index of the environment. A comparison of the experimental findings with numerical simulations shows a good agreement.