We report the growth of AlGaN/GaN heterostructures on conventional c-axis-oriented and vicinal-cut (0 0 0 1) sapphire substrates by metalorganic chemical vapor deposition (MOCVD). By maintaining the same growth conditions using these two different sapphire substrates, we were able to achieve comparably lower dislocation density and improved crystal quality for the AlGaN/GaN heterostructure grown on 1 degrees-tilt sapphire substrate. Furthermore, the growth on 1 degrees-tilt sapphire substrate followed a step-flow mode without the formation of two-dimensional islands, and holes (defects) therefore could not be formed through incomplete island coalescence. The corresponding dark leakage current of epilayers, grown on 1 degrees-tilt sapphire substrate was two orders of magnitude smaller compared to the one on c-axis-oriented substrate. (C) 2007 Published by Elsevier B.V.