Splitting of the excitonic peak in quantum wells with interfacial roughness

Excitons in a quantum well depend on the interfacial roughness resulting from its growth. The interface is characterized by islands of size ξ separated by one monolayer steps across which the confining potential decreases by V₀ for wider wells. A natural length is the localization length ξ₀=π/√2MV₀ characterizing the minimum size island to confine an exciton. For small islands (ξ<ξ₀), the absorption spectrum has a single exciton peak. As the island size ξ exceeds the localization length ξ₀, the peak gradually splits into a doublet. Generally the spectra exhibit the following features: (1) the shape is very sensitive to ξ/ξ₀ and depends only weakly on the ratio of island size to exciton radius; (2) in the small island regime ξξ₀, the asymmetric shape of the exciton peak is correctly described by a model of white-noise potential, except for the position of the peak which still depends on the correlation length of the disorder.