Control of GaP and GaAs nanowire morphology through particle and substrate chemical modification

We demonstrate two very different morphologies for GaP and GaAs nanowires grown by Au-assisted MOVPE on Si(111) substrates: rodlike wires and tapered wires with sharp tips. We show that the morphology is related to the stability of the particles at the wire tips during growth, and we propose that the mechanism of this effect is diffusion of Au away from the tip. Diffusion occurs, leading to tapered wires, only if there is a clean Si surface to act as a reservoir for the Au. Furthermore, the presence of indium in the particles, even at background levels from previous growth runs, inhibits the migration of Au. These results demonstrate a dramatic example of the sensitivity of wire morphology to substrate and particle chemistry, which could provide an important tool to tune nanowire morphology through particle alloying or surface treatment.