In this study, we have found that the lateral homoepitaxial growth on GaN nanowires is suppressed by introducing hydrogen gas into the plasma-enhanced chemical vapor deposition (PECVD) apparatus for the growth of GaN nanowires. The formation of GaHx (x= 2, 3) species due to the reaction between gallium atoms and hydrogen plasma is shown to decrease the amount of excess gallium atoms adsorbed on GaN nanowire surfaces, which results in the elimination of nucleation on the nanowire surface and thus improves the surface smoothness of the nanowire. The stacked-cone nanostructures appear under low hydrogen or hydrogen-less conditions, but completely disappear under high hydrogen conditions in the PECVD system. The mechanism of the elimination of lateral growth on the nanowire surface is further proposed. (C) 2012 Elsevier B.V. All rights reserved.