Selective Growth of ZnO Nanorod Arrays on a GaN/Sapphire Substrate Using a Proton Beam Written Mask

ZnO nanorod arrays were grown on a GaN/sapphire substrate in a controllable way using a hydrothermal growth method. Proton beam writing (PBW), a direct-write 3D lithographic technique, was used to pattern a polymethyl methacrylate (PMMA) mask spin-coated on to a GaN substrate. ZnO, which has the same wurtzite crystal structure and a low lattice misfit of about 1.9% compared with GaN, nucleated and grew into vertical rods at positions where the GaN was exposed. The structural and optical characteristics of the ZnO nanorods were further investigated using X-ray diffraction (XRD), and microphotoluminescence spectroscopy (mu-PL). Annealing of the ZnO nanorods in nitrogen gas significantly improved the ultraviolet (UV) light emission at 380 nm wavelength, and successfully decreased the yellow and green band emission considerably. These results show new potential applications for devices based on ZnO nanostructures.