THEORETICAL STUDIES OF THE STRUCTURAL, ELECTRONIC AND OPTICAL PROPERTIES OF THE COMPOUNDS BASED ON THE ELEMENTS OF II, IV AND VI GROUPS

Abstract

We report on theoretical study of the structural, electronic and optical proper- ties of semiconductors using the full{potential linearized augmented plane wave method (FP{LAPW) in the framework of density functional theory (DFT). This study includes the rocksalt{like compounds GeTe, SnTe and PbTe, the anti°uorite compounds Be2C, Mg2C, Mg2Si and Mg2Ge and the Nowotny{ Juza compounds LiZnN, LiZnP, LiZnAs and LiCdP. The obtained results are in good agreement with the available experimental data. The bandgap of the rocksalt compounds and LiZnN, show an anomalous be- havior; it decreases when the atomic number decreases. The small bandgap of LiZnN compared to LiZnP can be attributed to the anion p{cation d repulsion e®ects. The study of the optical properties shows that the dielectric constant decreases with increasing the cation atomic number for the rocksalt-like and anti°uorite compounds and increases with increasing the anion atomic number for the other studied compounds. The elastic properties and the valence charge density distribution show that the ¯lled tetrahedral compounds LiZnP, LiZnAs and LiCdP have a covalent bond (e.g., Zn{As) and ionic one (e.g., Li{As) so that they can be character- ized as half{ionic and half{covalent semiconductors. Finally, the study of the e®ect of hydrostatic pressure on the electronic and optical properties shows that the anti°uorite compounds follow the same be- haviour as the elemental diamond{like semiconductors, silicon and diamond. However, the small values of Be2C pressure coe±cients compared to those of diamond are attributed to the ionic nature of the Be{C bond in Be2C.