c-Axis-aligned InN nanocolumn arrays were vertically grown on 3 mu m GaN epilayers with InGaN buffer layers by radio-frequency molecular beam epitaxy without any catalysts X-ray diffraction transmission electron microscopy and field-emission scanning electron microscope were used to study the structural properties of the nanocolumns It has been found that without InGaN buffers InN films rather than nanocolumns were grown even at the same N/In ratio In addition high-quality InN nanocolumns can grow faster on InGaN buffers The growth mechanism was discussed and the joint actions of the gas-solid and Volmer-Weber modes promote the nucleation and the growth of InN nanocolumns (C) 2010 Elsevier B V All rights reserved