Experimentally observed two-exponential decay of excitonic transitions in GaAs-Al Gal -As multiple quantum wells has been successfully interpreted in terms of the exciton transfer between the continuum (free carriers) and the bound states. The calculation results obtained from this exciton-transfer model are in excellent agreement with experimental observations. The rates of the exciton transfer and the free-carrier recombination have been obtained. We have demonstrated that the emission-energy

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... dependence of the decay time constant of the slower decay component is caused by the variation in exciton binding energy induced by interface roughness in the quantum wells.