We report the self assembled growth of inclined and highly ordered GaN nanorods on (10 - 10) m-plane sapphire by metal-organic chemical vapor deposition, without metal catalyst. To determine the growth mechanism we performed a systematic study of the effect of the SiH4 flow, V/III ratio, growth temperature and growth time on growth behavior, demonstrating that optimized parameters were required for the growth of nanorods with high aspect ratios. High resolution X-ray diffraction showed that the nanorods were inclined at an angle of 58.4 degrees with respect to the substrate normal and followed a well-defined epitaxial relationship with respect to the on-axis plane of the nanorods, the (11-22) semipolar plane, and the (10-10) m-plane sapphire. Finally cathodoluminescence showed that the near band edge emission of the Si-doped nanorod was asymmetric and broad owing to the band filling effect resulting from high carrier concentration, compared to the undoped GaN. (C) 2014 Elsevier B.V. All rights reserved.