Ab–initio Calculations of Structural and Electronic Properties of a BexZn1-xSe Ternary Alloy
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Date
2012-06
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Addis Ababa Universty
Abstract
We 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.
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Keywords
BexZn1-xSe