In this paper, a study is presented on the effect of In on the surface morphology of GaN grown by HYPE. Experiments are performed with N-2 and H-2 as the carrier gasses, both with and without In present in the reactor. The adding of In increases the morphological quality of the grown layers; this effect is most strongly observed for N-2 as the carrier gas. It is found that adding In reduces the growth rate and also increases the steepness of the growth hillocks on the surface. The step velocity, which is calculated from hillock slopes and the growth rate, decreases upon adding In. Without In, trails are visible across the surface where steps are distorted by passing a dislocation outcrop. With In present this pinning is still present, however, the trails do not form. Two possible explanations for this phenomenon are an increased surface diffusion due to a mono- or bi-layer of In on the surface and the slower step motion when In is present. (C) 2007 Elsevier B.V. All rights reserved.