Exciton linewidth narrowing in thin-barrier GaAs/AlxGa1−xAs superlattices

Exciton line widths in GaAs/${\mathrm{Al}}_{\mathrm{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$As superlattices (SL’s) were found to decrease significantly with decreasing barrier widths ($L_b$’s). The observation was made with a series of SL samples at 15 K using photoluminescence excitation spectroscopy. The sample parameters were chosen in such a way that a wide range of n=1 subband dispersion was present in the series. The observed linewidth narrowing can be explained by a theory which incorporates the effect due to layer-width fluctiations within the coherent potential approximation, but ignores lateral variations in the layers.