Mazher, Javed (Professor)Mulualem, Getasew2018-07-122023-11-182018-07-122023-11-182012-06http://etd.aau.edu.et/handle/12345678/8378We have used the ab-initio SIESTA code within the framework of DFT, LDA method to calculate the structural and electronic properties of BexZn1-xSe alloy for different compositions x = 0.0, 0.33, 0.66, and 1.0. The system is modelled in various possible configurations using a large 54-atom supercell. It is noteworthy to mention that the determination of structural and electronic properties of a BexZn1-xSe ternary alloy at x = 0.33 and 0.66 have not been reported earlier to the best of our knowledge. We analyze composition effect on lattice constants, bulk modulus, pressure derivative, bandgap, and density of states. Deviations of the lattice constant from Vegard’s law and the bulk modulus from linear concentration dependence are observed. It was deduced that increasing the Be composition in the alloy increases the hardness of the materials. In addition, the calculated band structures showed that the bandgap undergoes a direct-to-indirect transition at the composition of 0.84. The bandgap is found to vary non-linearly with Be composition. Using the approach of Bernard and Zunger, the microscopic origins of bandgap bowing is also explained. It is concluded that the energy bandgap bowing is primarily due to volume deformation effect. Furthermore, the structural phase transformations of ZnSe under high pressure are also studied by similar method. It is found that ZnSe undergoes a first-order phase transition from the zinc blende structure to the rock salt structure at approximately 13.75 GPa. The ground state properties of the phases of ZnSe are also calculated. Our results are in good agreements with experimental observations.enBexZn1-xSeThesis