Transition from Au to pseudo-Ga catalyzed growth mode observed in GaAs nanowires grown by molecular beam epitaxy

We investigate the correlation between the Ga concentration of the catalyst droplet and the adopted crystal structure of individual GaAs nanowires grown by molecular-beam epitaxy using Au as a catalyst material. Through a postgrowth analysis the Ga content of the catalyst droplet during growth is estimated and related to the observed crystal structure of the nanowires. Depending on the Ga concentration, we observe a transition from typical Au catalyzed to pseudo-Ga assisted nanowire growth: Nanowires with low Ga concentration of the catalyst droplet during growth form predominantly wurtzite crystal structures. For Ga concentrations higher than 75 at. %, which we refer to as the pseudo-Ga assisted growth mode, the probability to form zinc-blende segments is strongly enhanced owing to the reduced droplet surface energy of the catalyst.