Rapid thermal annealing studies were performed on a 10-stack InAs/In0.15Ga0.85As dots-in-well (DWELL) heterostructure at four different temperatures of 700degreesC, 750degreesC, 800degreesC and 850degreesC. Optical and structural characterization were performed, using photoluminescence (PL) and double crystal X-ray diffraction (DCXRD) techniques. Based on the calculations and analysis of the PL peak positions and linewidths, the changes in the perpendicular and parallel lattice constants and the average indium composition in the DWELL structure were determined. Increased In/Ga interdiffusion along the growth direction and a thermally induced strain relaxation was observed. Good correlation between PL and XRD measurements has also been obtained. (C) 2002 Elsevier Science B.V. All rights reserved.