Effects of wave-function delocalization on the optical properties of GaAs/AlAs short-period asymmetric superlattices

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Abstract
We have conducted a high-pressure study of asymmetric-period GaAs/AlAs superlattices in order to observe the effects of inter-GaAs-well electronic coupling on the superlattice optical luminescence properties with varying AlAs layer thickness and approximately constant GaAs thickness (∼20 Å). When the AlAs layers are thick (60 Å), confinement shifts the GaAs Γ-like state well above the AlAs X-like state in the conduction band, producing a type-II band alignment. For decreasing AlAs thickness, the X-like state shows increasing confinement energy while the Γ-like state drops in energy due to wave-function delocalization across the barriers. Simultaneously the pressure coefficient of the GaAs-AlAs valence-band energy difference approaches zero for thinner barriers. We interpret this as evidence that the superlattice valence band loses its square-well nature in the thin-barrier limit.