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〉 and 〈10−10〉 axes.
Near-band-edge PL show good crystal quality, Raman spectra show finite size effects.