Level Repulsion of Localized Excitons in Disordered Quantum Wells

The spectral autocorrelation for a set of over 400 near-field photoluminescence spectra of a nar-row quantum well has been evaluated. It is compared with a microscopic model of an exciton in a disorder potential. The analysis provides strong evidence for quantum mechanical level repulsion and allows a quantitative estimate of the microscopic disorder features. The concept of participa-tion ratio is invoked to quantify the exciton center-of-mass localization lengths. These turn out to be broadly distributed and increase rapidly with energy. The connection between the spectral broadening of an exciton line in a quantum well (QW) and the presence of structural disorder has been known for two decades [1]. The center of mass (COM) of the exciton is subject to energy fluctuations originating from interface and alloy disorder present in the heterostructure. Consequently, exciton states are randomly localized with an inhomogeneous distribution of eigenenergies. Within certain approximations, the inhomogeneous exciton can be mapped onto the more gen-eral problem of a quantum mechanical particle in a disordered potential [2]. Despite this connection and the accurate existing experimental characterizations [3–5], however, the interpretation of experiments is mostly of qualitative and empirical nature, ofte