Effects of the layer thickness on the electronic character in GaAs-AlAs superlattices

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Abstract
Realistic tight‐binding calculations for the GaAs‐AlAs superlattice clearly demonstrate that if the GaAs layer thickness is less than ∼30 Å, the lowest conduction‐band state is confined to the AlAs barrier region instead of the GaAs quantum well region resulting in a spatial separation of electrons and holes. This observation exemplifies a failure of the widely used Kronig–Penney model and emphasizes the importance of the k vector selection rule. This property can be used in photoluminescencespectroscopy to determine the band offset of thin layer superlattices for an essentially arbitrary composition of Al x Ga1−x As. A complete two‐dimensional map of the electronic character as a function of the GaAs and the AlAs layer thickness is obtained. The possibility that X x y states may lie below X z states for narrow wells is proposed, and implications of the present calculation on interpreting spectroscopic data are discussed.