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Etude vibrationnelle des alliages semi-conducteurs II-VI et III-V : simulations empirique et ab initio

Abstract : Our work is devoted to promoting the percolation model using phenomenological methods which are independent and free from any need of external parameters. We used for this purpose existing ab initio codes (PWscf and SIESTA) and developed a semiempirical method to study the vibrational properties of AxB1 xC alloys. The technical parameters of the PWscf code were tested on ZnSe, BeSe ZnTe binary compounds, for which we have confronted our results with theoretical and experimental data available. The percolation model validation was done on the alloy Zn(Se, Te) belonging to the category of 1-bond ! 2-modes semi-conductors. We have confirmed the general bimodal behavior provided by the percolation model showing its existence for each bond Zn Se and Zn Te. The vibrational and structural properties of Zn(Se, Te) were calculated for different concentration using optimized cells of 64 atoms. The results are in good agreement with experiments. We present in detail our semi empirical method of calculating the spectrum of phonons, in principle applicable to all alloys without restriction on the size of super-cells. The development was carried out on (Zn, Be)Se and (In, Ga)As alloys with cells of up to 64 atoms relaxed from first principles. The application of our method to (In, Ga)As at 50% simulated by a super-cell of 8.103 atoms with a harmonic relaxation potential underlines the fact that the study of phonons in alloys requires the use of supercells which adequately describe the alloy disorder.
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Ayoub Nassour. Etude vibrationnelle des alliages semi-conducteurs II-VI et III-V : simulations empirique et ab initio. Autre [cond-mat.other]. Université Paul Verlaine - Metz, 2008. Français. ⟨NNT : 2008METZ040S⟩. ⟨tel-01752606⟩



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