We investigate the optical properties of strain-free mesoscopic GaAs/Al(x)Ga(1-x)As structures (MGS) coupled to thin GaAs/A(x)Ga(1-x)As quantum wells (QWs) with varying Al content (x). We demonstrate that quenching the QW emission by controlling the band crossover between AlGaAs X-point and GaAs Gamma-point gives rise to long carrier lifetimes and enhanced optical emission from the MGS. For x = 0.33, QW and MGS show typical type-I band alignment with strong QW photoluminescence emission and much weaker sharp recombination lines from the MGS localized exciton states. For x >= 0.50, the QW emission is considerably quenched due to the change from type-I to type-II structure while the MGS emission is enhanced due to carrier injection from the QW. For x >= 0.70, we observe PL quenching from the MGS higher energy states also due to the crossover of X and Gamma bands, demonstrating spectral filtering of the MGS emission. Time-resolved measurements reveal two recombination processes in the MGS emission dynamics. The fast component depends mainly on the X-Gamma mixing of the MGS states and can be increased from 0.3 to 2.5~ns by changing the Al content. The slower component, however, depends on the X-Gamma mixing of the QW states and is associated to the carrier injection rate from the QW reservoir into the MGS structure. In this way, the independent tuning of X-Gamma mixing in QW and MGS states allows us to manipulate recombination rates in the MGS as well as to make carrier injection and light extraction more efficient.
Vanessa Ors Gordo, Leonarde Nascimento Rodrigues, Floris Knopper, Ailton J Garcia, Fernando Iikawa, Odilon D. D. Couto Jr. and Christoph Deneke