SENSITIVITY OF RESONANT EXCITATION AND PHOTOLUMINESCENCE EXCITATION MEASUREMENTS TO EXCITON LOCALIZATION EFFECTS IN GAAS/ALGAAS QUANTUM-WELLS

Low temperature (2 K) photoluminescence (PL), PL excitation (PLE), and resonant excitation (RE) measurements on a very high quality, 150-angstrom-wide GaAs/Al0.3Ga0.7As multiquantum well structure are reported, with a focus on exciton localization effects. The PL spectra show evidence of effective submonolayer well width fluctuations. Excitons observed via RE are found to be predominantly localized; i.e., they decay from the same effective well-width region in which they are formed, while both localized and delocalized excitons are observed in PLE measurements. Delocalized excitons are free to diffuse to differing effective well-width regions which are energetically accessible. These results are supported by time-resolved PL measurements, which show essentially identical time-responses for differing effective well-width regions under resonant excitation conditions, thereby demonstrating the localized nature of resonantly created excitons.