The step-behavior of InGaN thin films grown on sapphire substrates by metal organic vapor phase epitaxy was studied using atomic force microscopy characterization. Spiral size and interstep distance decreased when the supersaturation of the group-III source was increased. Using this dependency and the Burton, Cabrera, and Frank model, the step energy was calculated to be 2.6 J/m(2) for InN in InGaN and 1.5 J/m(2) for GaN. InGaN spiral growth on sapphire substrates is caused by the specific large step energy of this material. Therefore, reducing dislocation densities in the epitaxial layers is most effective for reducing spiral densities. This was confirmed by growing InGaN on FIELO-GaN substrates, which have a low dislocation density.