We have studied the interdiffusion process on the group V sublattice in thermally annealed, undoped strained single quantum wells by comparing the results of contactless electro-reflectance spectroscopy with theoretically estimated optical transition energies. We show that the interdiffusion process in this system is Fickian. We estimate the activation energy for the interdiffusion process to be , which is low compared to those reported for other III-V-alloy-based heterostructures.