GaAs nanowires are obtained by the self-catalyzed method, where Ga droplets gather As molecules and participate in the nanowire growth. For the growth to be sustained, the droplets must be continuously fed with Ga.
Physical Review B 77, 155326 (2008)
Appl. Phys. Lett. 92, 063112 (2008)
Growth on silicon: Due to the lack of polarity, the orientation of the nanowire seed can have various orientations. This, in combination with twinning phenomenon occurring in the three dimensions of space, leads to discretized orientations of the nanowires in space. With careful tuning of the conditions, the orientations can be controlled.
Nano Lett. 11, 3827 (2011)