Computational modelling of the electronic and structural properties of chalcopyrite-type semiconductors and platinum group metal chalcogenides

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Silungwe, Dennis
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University of Zambia
An important aspect in the development of semiconducting devices for use in photovoltaic systems is the design of materials with appropriate band gaps. Electronic structure calculations based on Density Functional Theory (DFT) have been extensively used to study and to describe such properties of many condensed matter systems. In this work, we have utilized DFT to study the electronic properties of eight chalcopyrite-type semiconductors which are transition-metal type and hence are strongly correlated materials. For our chosen systems we first used the Local Density Approximation (LDA) and Generalized Gradient Approximation (GGA) energy exchange correlation functionals within DFT as implemented in the Quantum Espresso (QE) computer simulation package. The results from these two functionals predicted band gaps which were greatly underestimated and thus predicted metallic behaviour for some of the materials. These materials are termed as strongly correlated because they have incompletely filled d or f-orbitals and valence electrons in these materials have a complex influence on their neighbours. To circumvent this challenge the DFT+U method, which uses orbital-dependent potentials, is applied. With the application of the DFT+U method the results obtained were a great improvement over those obtained by LDA and GGA. An empirical shift method was also employed.
Semiconductors , Density Functional Theory , Solid State Electronic , Chalcopyrite