Effects of experimental parameters on the growth of GaN nanowires on Ti-film/Si(1 0 0) and Ti-foil by molecular beam epitaxy

•GaN nanowire are grown on 300 nm Ti-film/Si(100) and Ti-foil by plasma assisted MBE.•Nearly vertical nanowires can be grown on Ti-films covered with amorphous TiOx or TiOxNy.•The orientation of GaN nanowires grown on nitridated Ti-foil is determined by the grain alignment of the original Ti-foil.•A compilation of the growth parameters and their effects on GaN physical properties is given.