The role of coherence length of excitons in thin quantum wells

Using time-resolved luminescence we measure the energy relaxation of excitons in thin quantum wells. We find that the excitons relax by losing potential energy in a drift-diffusion motion driven by potential fluctuations in the quantum well plane, which are longer than the coherence length of the excitons. For a constant interface quality the coherence length strongly decreases with decreasing well width so that drift-diffusion dominates the exciton relaxation in thin quantum wells. © 1992.