Propriétés électroniques et thermiques des composés de type II-VI semiconducteurs de structure zincblende par la méthode ab-initio et les techniques DRX et EXAFS

Abstract

This work focuses on the study of the electronic and thermal properties of ZnSe and ZnS com pounds with a zincblende structure, with a view to their potential applications in various fields. The approach used combines the ab-initio, DRX and EXAFS methods. The results obtained from the simulation of the ab-initio equations show that these materials have direct band gaps at the Γ point of high symmetry. The band gap values are 1.18 eV for ZnSe and 2.02 eV for ZnS. These values differ from those reported in the literature, which are 2.7 eV for ZnSe and 3.72 eV for ZnS under the same conditions (room temperature), but are in good agreement with other authors using the same method. The band structures and DOS obtained in this study are also innovative compared with those in the existing literature. Charge density analysis reveals that the ionic character is more pronounced in ZnS than in ZnSe. Similarly, Bragg diffractograms (DRX) show that the peaks have the same parity, confirming that the ZnSe and ZnS compounds crystallize in the zincblende structure. Exploration of cumulants using the EXAFS technique shows a strong temperature dependence in these compounds. Fits to the Einstein model of the parallel and perpendicular MSRD reveal this temperature dependence. This temperature dependence affects the movement of the atoms, thus disturbing the behavior of the electrons, which lose their preferred direction. This strong temperature dependence presents a marked anisotropy in these compounds. Indeed, evaluation of this anisotropy shows that χ is not equal to 1 whatever the coordination layer of the compounds studied, which is in line with predictions in the literature. These results contribute to technological advances and the development of applications in fields such as electronics, renewable energies, health, etc.