Vertically aligned Ga-doped ZnO (ZnO:Ga) nanorods were grown on sapphire substrates without buffer layers under conditions designed to ensure rapid growth rates with a magnetron sputtering system. Unlike the undoped ZnO layer with microsize protrusions, the 1 and 2 wt% Ga doping induced the formation of uniform nanorod arrays with epitaxial growth behavior. In the initial growth stage, the ZnO:Ga layers exhibited island growth with pyramidal shapes due to enhanced misfit strain. This promoted preferential growth along the c-axis, resulting in the formation of nanorod arrays,without buffer layers. However, the increased stress stored in the ZnO:Ga layers generated high density of stacking faults, which led to an intense donor-acceptor pair emission at 3.31 eV. In addition, the sample doped with a high Ga amount (2 wt%) had rotated crystal phases, resulting in rough sidewalls with nano-branch or sawtooth shapes. (C) 2011 Elsevier B.V. All rights reserved.