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Excitonic Complexes in Natural Quantum Dots Formed in Type II GaAs/AlAs Structures

Abstract : Quantum dots with strong three dimensional confinement and low surface density 106cm-2 have been identified in a structure which was nominally grown as a type II GaAs/AlAs bilayer surrounded by GaAlAs barriers. The unique type II system makes the dots easy to detect due to characteristic, very long-lived (ms range) indirect two-dimensional excitons. The 2D excitons efficiently diffuse (up to 100mm) into zero-dimensional traps, which is difficult to obtain in conventional, direct type structures. The dots can therefore be effectively filled by excitons, giving rise to the formation of not only excitons, charged excitons and biexcitons, but also more complex excitonic molecules which show a multiple zero-dimensional shell structure.
This work is devoted to investigations of the nature, process of formation and interactions in the strongly confined exciton complexes system.
Spectroscopic studies of single quantum dot emission under different conditions of excitation and detection are presented.
The possibility of optically controlling the number of electrons and holes populating the discrete dot energy levels allows a discussion of the exciton complexes formation depending on exciton densities. The observed effects are described in the band-gap renormalisation model including many-body, exchange, and correlation type interactions.
The influence of a magnetic field on the exciton complexes is discussed. In general, it is shown how the application of a magnetic field modifies the energy structure of the observed transitions. Typical quantum dot properties such as Zeeman splitting, diamagnetic shift, and exciton binding energy are discussed. They allowed an analysis of the symmetry and size of the dots' confining potential.
Moreover, the mechanisms of exciton capture in the dots are considered. The important role of diffusion processes revealed in single dot time resolved experiments is discussed.
The role of radiative and non-radiative processes in the multiexciton emission is shown in temperature activated emission from a single dot.
Photon correlation experiments allowed to classify the number of multiexciton emission lines, to study the character of capture of photo-created carriers, and to investigate the dynamics of charge fluctuations characteristic of a single quantum object.
The experimental approach to a single quantum dot problem is widely discussed, and theoretical models are applied to describe the observed effects.
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Submitted on : Monday, October 15, 2007 - 2:19:17 PM
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Barbara Pietka. Excitonic Complexes in Natural Quantum Dots Formed in Type II GaAs/AlAs Structures. Physics [physics]. Université Joseph-Fourier - Grenoble I, 2007. English. ⟨tel-00179386⟩

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