Layer interface roughness effects in the coherent intraband transitions of excitons in quantum well structures

Using photoluminescence spectroscopy we study the effects of exciton localization and interface growth islands in the coherent intraband transitions between the exciton states associated with the first and second conduction subbands. We show that the growth islands can act as submicron quantum systems with distinct energy-level configurations. Our results show that these systems interact differently with an intense infrared laser, causing a nearly two-dimensional medium with spatially modulated optical properties. We also show that the exciton localization enhances the coherent intraband transitions and discuss how these transitions can be used to study morphology of the interfaces between quantum well layers.