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Réexamen du comportement vibrationnel des alliages modèles GaAs(1-x)Px et Si(1-x)Gex : modèle de percolation et calculs ab initio

Abstract : The 1-bond 2-TO percolation generic scheme proposed for the basic understanding of the vibra-tion spectra (Raman and Infrared IR) of usual random semiconductor alloys with zincblende structure, which has recently challenged the standard MREI (modified-random-element-isodisplacement) model with the 1-bond 1-TO behavior, (Chang et Mitra, 1971) developped in the sixties, is here confronted to the cluster model (Verleur et Barker, 1966) which has been accepted through use for the study of the vibration spectra of these particular zincblende alloys, which obviously exhibit more than one phonon mode per bond in their vibration spectra. In fact, the IR reflectivity spectra of GaAs1-xPx, the representative alloy of the last class, i.e. those very ones which motivated the developpement of the cluster model in the sixties, find a natural explanation in the scope of the percolation model on the basis of a perfect random substitution As P, with no adjusta-ble parameter. With this, GaAs1-xPx and its like are rehabilitated as random alloys in principle, and further, the percolation paradigm generalizes to all types and subtypes of the traditional four-type classification of phonon mode behavior of semiconductor alloys, based on the MREI and cluster models. In a second stage, we investigate to which extent an extension of the percolation scheme to the di-amond structure may help to understand the mysterious nature of the Raman behavior of the representative Si1-xGex alloy. We realize that a good simulation of the Si1-xGex Raman spectra already existing in the literature can be obtained with no adjustable parameter but the Raman efficiency of the Si1-xGex bond within a generic 1-bond?N-TO version of the percolation model, where N indicates a sensitivity to the local environment of the Ge-Ge (N=1 non sensitive), Si-Si (N=2, sensitive to the first neighbor environment) and Si-Ge (N=3, sensitive to the second neighbor environment) bonds. Some differences between the GaAs1-xPx and Si1-xGex percolation patterns are attributed to the different natures of the lattice relaxation in the zincblende and di-amond structures (inversion of the order of like branches in the Si-Ge triplet) and to the spectacular disper-sion of the Ge-Ge like modes (anti parallelism of the unique Ge-Ge branch) and Si-Si (inversion of the order of like branches in the Si-Si doublet), which add to the local constraint effect, the only one usually taken into account in the zincblende alloys examined so far. The assignment of the individual phonons branches in each percolation scheme, i.e. GaAs1-xPx or Si1-xGex, is achieved via home-made ab initio phonon calculations with a focusing on bond-stretching along prototype impurity motives designed as quasi linear so as to be remain in with the spirit of the linear chain approximation on which the percolation model is based
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Jihane Souhabi. Réexamen du comportement vibrationnel des alliages modèles GaAs(1-x)Px et Si(1-x)Gex : modèle de percolation et calculs ab initio. Autre [cond-mat.other]. Université Paul Verlaine - Metz, 2010. Français. ⟨NNT : 2010METZ025S⟩. ⟨tel-01752963⟩



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