In this work, we present evidence of an interaction between surface morphology and strain relaxation in InAlAs graded buffer layers. Different structures have been designed to carefully investigate the influence of the growth parameters on the relaxation process. By combining X-ray reciprocal space mapping, transmission electron microscopy and atomic force microscopy, we clearly show that improvement of the surface morphology is obtained by controlling the introduction of dislocations, and especially beta dislocations (aligned in the [1 1 0] direction). The arsenic pressure is also found to be a critical parameter which influences this morphology as well as periodic composition modulations in the InAlAs graded layers. Two scales of modulations have been evidenced, with two different periodicities (similar to 50 and similar to 10 nm). (C) 2002 Elsevier Science B.V. All rights reserved.