We study the role of As during InAs quantum dots (QDs) growth by molecular beam epitaxy using reflection high-energy electron diffraction (RHEED). We observe that the RHEED intensity transient onset and the transition to the saturation region occur at less InAs thickness under higher As-4 flux. From the RHEED transients, we find that the diffusion time does not depend on the As-4 flux while the diffusion barrier does. The diffusion length of In adatoms can be reduced by increasing the diffusion barrier using higher As-4 flux, allowing us to grow InAs QDs at higher densities. (c) 2013 Elsevier B.V. All rights reserved.