When self-assembled InAs/GaAs(0 0 1) quantum dots (QD) are overgrown by a thin (2 nm) GaAs cap under different growth conditions, morphological changes occur. The effects of growth conditions on the final structural properties are analyzed by atomic force microscopy. Under As-4, thin cap deposition at similar to 540degreesC produces elongated dash-like nanostructures, whereas at 500degreesC two humps are obtained from each QD. When As-2 is used and the thin cap is deposited at 500degreesC, quantum rings are obtained. Ensemble photoluminescence (PL) spectroscopy and polarization PL at 15 K show drastic changes on confinement properties. Shape control results in PL emission tuning from 1110 nm (dots) to 920 nm (rings). (C) 2003 Elsevier Science B.V. All rights reserved.