Structural and optical properties of In0.5Ga0.5As/GaAs quantum dots (QDs) grown at 510degreesC by atomic layer molecular beam epitaxy technique are studied as a function of n repeated deposition of I-NIL-thick InAs and 1-MLthick GaAs. Cross-sectional images reveal that the QDs are formed by single large QDs rather than closely stacked InAs QDs and their shape is trapezoidal. In the image, existence of wetting layers is not clear. In 300 K-photoluminescence (PL) spectra of InGaAs QDs (n = 5), 4 peaks are resolved. Origin of each peak transition is discussed. Finally, it was found that the PL linewidths of atomic layer epitaxy (ALE) QDs were weakly sensitive to cryostat temperatures (16-300 K). This is attributed to the nature of ALE QDs; higher uniformity and weaker wetting effect compared to SK QDs. (C) 2004 Elsevier B.V. All rights reserved.