A DFT Study on the Structural and Electronic properties of Cadmium Telluride (Cd&lt;sub&gt;n&lt;/sub&gt;Te&lt;sub&gt;n&lt;/sub&gt;) and Cadmium Zinc Telluride (Cd&lt;sub&gt;(n−m)&lt;/sub&gt;Zn&lt;sub&gt;m&lt;/sub&gt;Te&lt;sub&gt;n&lt;/sub&gt;) Clusters

M Weldetsadik,H Woldeghebriel

doi:10.4314/mejs.v7i1.117241

Abstract

In this study, the structural and electronic properties of CdnTen and Cd(n−m)ZnmTen clusters have been studied using the plane wave based density functional theory (DFT). The QUANTUM ESPRESSO/PWSCF package employing the local density approximation (LDA) for the exchange correlation potential is used. In all calculations, the geometry optimization was employed in allowing the structures to fully relax. Structural properties viz. geometry, bond length and electronic properties like HOMO-LUMO gap, binding energy, second order energy difference and nature of bonding have been analyzed. As a result, we obtained that the binding energy increases with increasing cluster size and doping level. Zinc doped CdnTen clusters show greater binding energy than the undoped clusters. Planar structures are obtained for very small cluster sizes and in our simulation three dimensional structure is found at Cd4Te4 cluster in the lowest energy geometry. Clusters of certain sizes often have special properties, i.e. higher stability or larger HOMO-LUMO gap when compared with other clusters, such as Cd(3−m)ZnmTe3, m = 0, 1, 2 clusters. Thus, we can take it as a building block in the growth of the structures in our calculation. The partial charge density distribution of the HOMO and LUMO levels for CdnTen and Cd(n−m) ZnmTen clusters show that, the HOMO levels are predominantly localized on the Te atoms and the LUMO levels are distributed on both Cd and Zn atoms. Moreover, the LUMO levels are delocalized at the center of the clusters due to the hybridization of the molecular orbitals. The LDOS and energy level plots show discrete lines at the atomic level and the discreteness disappears as the cluster size increases.

Highlights

Semiconductor nanoparticles or Quantum Dots (QDs), in particular II-VI materials, have received tremendous attention during the last decades owing to their unusual physical properties and wide range of applications
In this work structural and electronic properties of neutral and zinc doped cadmium telluride clusters are studied using QUANTUM ESPRESSO/ PWSCF package based on the principle of density functional theory (DFT), which in turn depends on pseudo-potential with a plane wave basis sets
The binding energy increases with increasing cluster size, the fact that constituent atoms in larger clusters have more neighbors resulting in strong interactions, i.e. the surface effect decreases with cluster size

Summary

INTRODUCTION

Semiconductor nanoparticles or Quantum Dots (QDs), in particular II-VI materials, have received tremendous attention during the last decades owing to their unusual physical properties and wide range of applications. According to Bhattacharya and Anjali (2007), small stoichiometric CdnTen clusters and a few nonstoichiometric CdmTen (for m, n = 1, 4, 13, 16, 19 and m n) clusters have been studied using the density functional formalism and projector augmented wave method within the generalized gradient approximation. They observed that, upon relaxation, the symmetry changes for the Cd-rich clusters whereas the Te-rich clusters retain their symmetry. We present a systematic study on the electronic and structural properties of Cadmium Telluride and Cadmium Zinc Telluride clusters using density functional theory. In all the structure optimizations, the force and energy convergence considered are 103eV/A and 104eV respectively

RESULTS AND DISCUSSION

CdTe dimer

CONCLUSION

ACKNOWLEDGEMNETS