Near-surface Ga1-xInxNyAs1-y/GaAs quantum well (QW) structures were grown and in situ annealed in a solid-source molecular beam epitaxy chamber equipped with a radio-frequency nitrogen (N-2) plasma source. It was found that the surface desorption and indium out-diffusion from the surface QW took place under annealing condition by atomic force microscope and X-ray photoelectron spectroscope. Ga/In atoms interdiffusion across the QW hetero-junctions and the change of composition fluctuation within the QW have been observed at elevated annealing temperatures by using double crystal X-ray diffraction (XRD) theta/2theta scans and transmission electron microscopy. The best fitting for the XRD results reveals a diffusion length of delta = 0.7 nm and 1.0 nm for 580degreesC and 680degreesC in situ annealing, respectively. (C) 2004 Elsevier B.V. All rights reserved.