Comparison of GaN nanowires grown on c-, r- and m-plane sapphire substrates

•Comparison of Ni-catalysed GaN nanowires (NW) grown on c-, r-, and m-plane sapphire.•Carrier gas, temperature, pressure and TMGa flow rate strongly impact NW growth.•Narrow growth parameter space for thin, non-tapering GaN nanowires.•NWs with triangular cross section grow along the 〈10−11〉〈10−11〉 and 〈10−10〉〈10−10〉 axes.•Near-band-edge PL show good crystal quality, Raman spectra show finite size effects.

Gallium nitride nanowires were grown on c-plane, r-plane and m  -plane sapphire substrates in a showerhead metalorganic chemical vapor deposition system using nickel catalyst with trimethylgallium and ammonia as precursors. We studied the influence of carrier gas, growth temperature, reactor pressure, reactant flow rates and substrate orientation in order to obtain thin nanowires. The nanowires grew along the 〈101¯1〉 and 〈101¯0〉 axes depending on the substrate orientation. These nanowires were further characterized using x-ray diffraction, electron microscopy, photoluminescence and Raman spectroscopy.