Speckle Analysis of the Excitonic Emission from Quantum Wells

In this work, optical properties of semiconductor quantum wells (QW) are investigated, which are relevant for the light pattern (speckle pattern) emitted in nonspecular directions by QW after resonant excitation of the exciton states. This secondary emission (SE) contains information on disorder and scattering processes in the sample. In particular, three main topics are investigated along this Thesis: • Spectral Speckle Analysis Speckles in the directionand frequency-resolved SE can be used for extraction of its coherent part, the Resonant Rayleigh Scattering (RRS). Furthermore, the frequency resolved lifetime of excitons within an inhomogeneously broadened ensemble can be established. A microscopic density matrix theory for excitons in interaction with acoustic phonons is developed and numerically solved. Good agreement with the experimental results for different QW sizes and temperatures is found. • Sloped Speckles QW with mechanical strain are considered. For a proper geometry, the strain leads to a spatially dependent modification of the emission energy. Furthermore, a tilting of the directionand time-resolved speckle pattern is experimentally observed. The theoretical description of the RRS allows to relate this tilting to the local value of the spatial gradient of the exciton energy. Numerical simulations make clear that this effect is not due to exciton motion along the strain gradient, but just relies on interference in an energetic landscape with systematic slope. • Non-Markovian exciton-phonon dynamics Non-Markovian effects in QW are investigated, where both pure dephasing and dephasing due to relaxation between different excitonic states are possible. The density matrix theory is here numerically solved beyond the Markov approximation for the interaction between excitons and acoustical phonons. The absorption spectrum consists of Lorentzian peaks on top of broader sidebands originating from the non-Markovian coupling. These features are mostly important for the strongly localized states in the low energy side of the spectrum, suggesting a better interpretation of near-field experiments.