Growth mechanism of GaN nanowires: preferred nucleation site and effect of hydrogen.

The growth mechanism of epitaxial GaN nanowires grown using particle-mediated chemical vapour deposition was investigated. By examining the diameter-dependent growth rate of GaN nanowires, we show that the kinetic reaction-limited growth of GaN nanowires originates from the combination of mono-nuclear and poly-nuclear growth rather than the Gibbs-Thompson effect. We present a generalized nucleation-mediated growth model to describe the diameter dependence of the nanowire growth rate and show that the nucleation of sources occurs at the vapour/liquid/solid three-phase boundary. From the same model, we demonstrate that increased hydrogen concentration in the carrier gas reduces the supersaturation, leading to a reduced GaN nanowire growth rate. Our approach can be applied to other nanowire materials systems, and it allows the determination of the preferred nucleation site during nanowire growth.