Improving the yield of GaAs nanowires on silicon by Ga pre-deposition.

GaAs nanowire (NW) arrays were grown by molecular beam epitaxy using the self-assisted vapor-liquid-solid (VLS) method with Ga droplets as seed particles. A Ga pre-deposition step is examined to control NW yield, diameter and morphology. The NW yield can be increased with suitable duration of a Ga pre-deposition step, but is highly dependent on oxide hole diameter and surface conditions. The NW diameter was determined by vapor-solid growth on the NW sidewalls, rather than Ga pre-deposition. The maximum NW yield with a Ga pre-deposition step was very close to 100%, established at shorter Ga deposition times and for larger holes. This trend was explained within a model where maximum yield is obtained when the Ga droplet volume approximately equals the hole volume.