We investigated the effects induced by Si during self-assembled InAs quantum dots growth by molecular beam epitaxy on GaAs (1 0 0) substrates. The GaAs surface was exposed at high substrate temperatures to Si molecular flux for a few seconds. Samples grown this way were compared with conventionally grown quantum dot samples. Atomic force microscopy (AFM) images showed significant differences between these two types of samples. Smaller size dispersion and an increase of island dimensions were observed for those samples exposed to the Si molecular flux. The photoluminescence spectra revealed a red shift of the quantum dots (QDs) emission. In order to evaluate the optical anisotropy of the QDs, reflectance difference spectroscopy (RDS) measurements were performed. (C) 2002 Elsevier Science B.V. All rights reserved.