We have fabricated stacked InAs quantum dot (QD) structures on InP(311)B substrate by using novel strain controlled technique, and investigated the role of At atoms which were used in strain-compensating spacer layers. Ultrahigh density (similar to10(12) cm(-2)) of 20 QDs stacks and significantly improved uniformity of QDs were achieved in samples with 20 nm-thick InGaAlAs strain-compensating spacer layers. From secondary ion mass spectrometry measurement, the composition of InGaAlAs layers was uniform, but a large fluctuation of composition was observed if InGaAs layers were used. We found that Al atoms prevent the segregation of In in InGaAlAs, and InAs QDs grown on these InGaAlAs strain-compensating spacer layers result in an uniform array in three dimensions on InP(311)B substrates. (C) 2003 Elsevier Science B.V. All rights reserved.