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Shape and dynamics of elastically strained quantum dots

Abstract : The aim of this thesis is to theoretically study the coarsening dynamics of self-organized quantum dots. To this end, we derive the spatio-temporal evolution equation for a hetero-epitaxial system which takes into account surface diffusion, elastic effect, capillary effect and anisotropic effect, using the continuous mechanics framework. We first investigate theoretically the 2D morphology and the dynamics of an isotropic and an anisotropic system of self-organized islands (quantum dots). In both cases, we find a quasi-analytical continuous family of solution which describes the shape and the size of the islands and is favorably compared to our numerical simulations. We find in both cases that the coarsening time depends linearly on the distance between the islands and remarkably that in the anisotropic case the coarsening time can be reduced or accelerated depending on the islands heights. Secondly, motivated by experimental results on GaN quantum dots we study a three-dimensional system with a hexagonal surface energy anisotropy symmetry. Our numerical simulations reveal that the coarsening time is strongly slowed down due to the presence of the surface energy anisotropy and that a transition from hexagonal to elongated islands appears as the initial height of the film increases. Finally, we include the effect of preferential evaporation and we recover islands without a wetting layer that are observed experimentally and have a high photo-luminescence emission efficiency in the UV spectrum.
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Guido Schifani. Shape and dynamics of elastically strained quantum dots. Quantum Physics [quant-ph]. Université Côte d'Azur, 2018. English. ⟨NNT : 2018AZUR4069⟩. ⟨tel-02089755⟩

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