Control of Seed Detachment in Au-Assisted GaN Nanowire Growths

Abstract

The detachment and migration of Au catalyst seeds in the Au-assisted growth of GaN nanowires are observed to be controlled by the partial pressure of gallium and nitrogen radicals in the plasma-enhanced chemical vapor deposition system. The migration rate of Au catalyst increases with increasing the gallium vapor pressure during the growth. With the increasing gallium partial pressure, the compositions of gallium in the Au−Ga seeds of nanowires increase, which dramatically enhances the instability and the detaching of Au seeds during the growth. Besides, the gallium atoms adsorbed on the nanowire surface may act as a surfactant to facilitate the Au migration. Therefore, the increase of gallium partial pressure increases the amount of gallium atoms adsorbed on the nanowire surface and further enhances the rate of Au migration along the nanowire. On the other hand, with the increase of gas phase nitrogen radical concentration, an increasing amount of nitrogen atoms can be adsorbed on the nanowire surface to hinder Au migration along the nanowire. In addition to the vapor−liquid−solid (VLS) growth process observed, the growth of GaN nanowires via the vapor−solid−solid (VSS) process is also observed. In VSS growth, the detachment of solid Au seeds was inhibited dramatically.