Self-assembled InAs quantum dots (QDs) covered by In0.15Ga0.85As layer with different thickness were grown by molecular beam epitaxy and their structural and optical properties were investigated by transmission electron microscopy (TEM) and photoluminescence (PL) spectroscopy. Cross-sectional TEM images showed that the shape of InAs QD, particularly the height, was controlled by changing the thickness of InGaAs overgrowth layer, thus changing the optical properties. The emission peak position of InAs QDs covered by 8.5 nm In0.15Ga0.85As layer was 1.30 mum at room temperature with the energy-level spacing between the ground states and the first excited states of 80 meV, which is about 1.5 times larger than that of InAs QDs capped by GaAs layer. The longer emission wavelength with relatively larger energy-level spacing was related to the QD aspect ratio (height/width) that was confirmed by TEM images. (C) 2003 Elsevier Science B.V. All rights reserved.