  We investigate the influence of modified growth conditions during the
spontaneous formation of GaN nanowires on Si(111) in plasma-assisted molecular
beam epitaxy. We find that a two-step growth approach, where the substrate
temperature is increased during the nucleation stage, is an efficient method to
gain control over the area coverage, average diameter, and coalescence degree
of GaN nanowire ensembles. Furthermore, we also demonstrate that the growth
conditions employed during the incubation time that precedes nanowire
nucleation do not influence the properties of the final nanowire ensemble.
Therefore, when growing GaN nanowires at elevated temperatures or with low Ga/N
ratios, the total growth time can be reduced significantly by using more
favorable growth conditions for nanowire nucleation during the incubation time.
