Using reflection high-energy electron diffraction, photoluminescence and atomic force microscopy, we have compared the growth of self-assembled InAs quantum dots (QDs) on AlAs(1 0 0) surfaces with that on GaAS(1 0 0). Due to the nearly identical lattice mismatch, we have observed the same critical thickness for the strained InAs wetting layer on both GaAs and AlAs. The main difference between the two systems is that the growth of InAs/AlAs QDs proceeds about two times slower (depending on the growth conditions). This is attributed to reduced In migration on the AlAs surface which also explains the smaller size and larger density of the QDs. Our results show that when the diffusion is enhanced, e.g. by increasing the substrate temperature, the QD density can be reduced which is of importance for single-QD device applications. (C) 2002 Elsevier Science B.V. All rights reserved.