We employed the postgrowth impurity-free vacancy diffusion technique to selectively tune the bandgap of the InAs/InGaAlAs dots-in-well laser structure grown on (100) InP substrate. A blueshift up to 170 nm with a significant decrease in the photoluminescence linewidth has been observed. Spatial control of the bandgap shifts has been achieved using SiO 2 and Si xN y layers as annealing caps. A differential wavelength shift of 76 nm has been observed after a rapid thermal annealing step at 750°C for 30 s. In contrast to most reported results in other material systems using similar process, we observed a larger bandgap shift from the Si xN y capped samples than from the SiO 2 capped samples. Our theoretical calculation indicates that the unusual intermixing behavior in this material system is governed by different interdiffusion rates of group-III atoms.