Random Potential Fluctuations in Thin Quantum Wells Probed by Localized Excitons

Abstract

GaAs/AlGaAs single quantum wells (QW) with different degrees of fluctuations of the exciton confinement potential are investigated by microphotoluminescence (μ-PL) as a function of the excitation energy and by conventional PL, PL excitation, as well as cathodoluminescence spectroscopy. The surface morphology has been studied by atomic force microscopy. For a small inhomogeneous broadening of the PL spectrum, the influence of resonant excitation of higher localized exciton states is only detected for energies below the center of the absorption line, which defines an effective exciton mobility edge Em. For broader PL spectra, resonant excitation of higher states can be observed far above the center of the absorption spectrum resulting in an effective blue-shift of Em. Furthermore, the position of Em can depend on the excitation location. In this case, in addition to nm-scale fluctuations, a variation of the random potential on the μm-scale was observed.