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

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 (\ensuremath{\sim}20 \AA{}). When the AlAs layers are thick (60 \AA{}), confinement shifts the GaAs \ensuremath{\Gamma}-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 \ensuremath{\Gamma}-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.