We have studied emission-wavelength extension of nitrided InAs/GaAs quantum dots (QDs) with different sizes. Nitrided QDs have been shown to suppress In segregation during the capping layer growth. The emission wavelength reaches 1.3 mu m at room temperature. Effects of the strain on the structural and optical properties of QDs have been investigated by photoluminescence spectroscopy and transmission electron microscopy. The nitrogen-incorporation process into the InAs QDs depends on the QD size at the moment of nitrogen irradiation. The large QDs are covered by a thin nitrided layer, while the small QDs tend to form nitrogen-containing alloys. (c) 2006 Elsevier B.V. All rights reserved.