# Zero-dimensional properties of self-assembled islands.

 Titre: Zero-dimensional properties of self-assembled islands. Auteur: Raymond, Sylvain. Résumé: The steady state and dynamic properties of semiconductor self-assembled island structures made from III-V materials are studied by photoluminescence and time-resolved photoluminescence. The islands layer contains a number of hemispherical caps with a low-gap material inside the cap and a high-gap material outside. The experiments performed are aimed at probing the nature of the bound states inside the islands, looking specifically at the dimensionality of these islands through the mapping of the density of states. First, a system consisting of an $\rm Al\sb{0.45}In\sb{0.55}As$ layer imbedded in an $\rm Al\sb{0.35}Ga\sb{0.65}As$ matrix emitting in the visible (red) is used to directly probe the properties of "individual" islands and compare them with different systems: two-dimensional (quantum well), one-dimensional (quantum wire) and zero-dimensional (quantum dot). The observed temperature independent linewidth and lifetimes are attributed to quantum dot properties. Next, the strong emission obtained under resonant excitation conditions in this system is used to study the influence of phonons on the relaxation processes in zero-dimensional semiconductor heterostructure systems. The other material system studied consists of a single $\rm In\sb{0.5}Ga\sb{0.5}As$ self-assembled layer imbedded in GaAs emitting in the infra-red. A model based on a quantum well with in-plane parabolic confinement is developed and compared with experimental results. Magneto-photoluminescence measurements reveal the symmetry of the electronic shell structure which is found to be consistent with the model developed, thus confirming the zero-dimensional nature of the carrier confinement. The presence of excited states is then exploited by studying the inter-sublevel dynamics of carriers in quantum dots. Despite the discreteness of the density of states, fast inter-sublevel dynamics is observed and all experimental observations are found to be consistent with state-filling dynamics for which the inter-sublevel relaxation is impeded only when lower energy levels are filled. Date: 1997 URI: http://hdl.handle.net/10393/4092

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