We have investigated theoretically and experimentally the impurity-free vacancy induced disordering for GaAs/AlGaAs double quantum well laser structure grown by MBE with capped SiO2 by repid thermal annealing. The position of the photoluminescence peaks, due to the n=1 electron to heavy-hole transition, was measured before and after annealing the samples. As a result, the samples annealed rapidly show blue shift in the position of photoluminescence peaks and the magnitude of shift increases with increasing temperature. We analyzed theoretically the Al-Ga interdiffusion process in GaAs/AlGaAs quantum well structure and the experimental energy shifts were compared with a theoretical model to obtain the diffusion coefficient of aluminum into the quantum well at different temperatures and the activation energy of aluminum diffusion process. The aluminum diffusion coefficient in the sample annealed at 950 ℃ for 30 s is 6.6×10-16 cm2/s. The activation energy found is 5.0 eV.