The growth of self-organized InAs(N) quantum dots on GaAs by molecular beam epitaxy has been investigated. Photoluminescence (PL) and transmission electron microscopy (TEM) experiments have been carried out to determine the influence of the growth temperature and nitrogen plasma exposure on the optical and structural properties of the dots. At low growth temperature, in the 410-450 degrees C range, some nitrogen is found to be incorporated in the quantum dots. This incorporation does not significantly affect their shape but causes a red-shift of the PL emission. At higher temperature, 510 degrees C, a bimodal distribution rapidly appears with nitrogen exposure. Cross-sectional TEM images reveal a first population of coherent dots whose shape is similar to that of InAs dots, and a second population of large, flat and occasionally relaxed dots: in that case the associated PL spectrum is typical of low density arrays of N-free InAs quantum dots. Discussion focuses on the different mechanisms involved in the dots growth. It is proposed that the occurrence of the second population of large dots is due to the defects and composition fluctuations induced by nitrogen at 510 degrees C. (c) 2006 Elsevier B.V. All rights reserved.