High-resolution photoluminescence measurements performed on several GaAs/Al0.25Ga0.75As multiquantum well structures revealed extremely sharp excitonic transitions separated in energies corresponding to roughly half-monolayer fluctuations in the well sizes. To understand these observations, a model for the interface in molecular beam epitaxy (MBE) is developed using studies of crystal growth. Results of this structural model are coupled with the theory of the effects of interface roughness on photoluminescence linewidth. A comparison of the experimental and theoretical studies shows that an interface formed under optimized growth conditions can be described by an interfacial layer made up of GaAs and AlGaAs islands. The sizes and the relative concentrations of these islands depend upon the precise instant at which the interface is formed. Consequences of this model for photoluminescence spectroscopy are discussed.
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Singh et al. (1985) studied this question.