Electrooptical properties of staggered alignment AlGaAs heterostructures

The authors report measurements of the electrooptic properties of staggered-alignment AlGaAs structures. These samples, grown by molecular beam epitaxy, have narrow GaAs layers, so that the AlAs X minima provide the lowest energy excited states for electrons, while holes are confined to the GaAs heavy-hole valence band. Following pulsed optical excitation of the spatially direct Γ-Γ transition within the GaAs layers, holes remain trapped in the GaAs layers, while electrons are rapidly transferred to the AlAs X minima. Subsequent recombination is both real-space and momentum-space forbidden, resulting in long excited-state lifetimes. While the carriers remain in the spatially separated excited states, there is a concomitant bleaching of the strong Γ-Γ absorption in the GaAs layers. A modification of the structure to include additional barrier layers between the active layers provides a mechanism by which the excited-state lifetimes can be increased at will. Conversely, the recombination times can be reduced through the application of external fields.