Estudo de vacâncias e falhas de empilhamento em ZnO Wurtzita

Abstract

Using ab initio calculations within the density functional theory and norm conserving fully separable pseudopotentials, we have studied the structural and electronic properties of ZnO. We have investigated the formation energies and eletronic structure of defects in ZnO. We calculated point defects: Zn and oxigen vacancies and a planar defect: stacking fault. The study of defects is essential to understand the behavior of the material and to tailor its numerous technological applications. Our work shows that the formation energy for oxygen vacancy is lower than that for Zn vacancy. For the Zn pseudopotential we use a core correction and add the d orbitals on the valence. This procedure makes the computational calculations heavy but the results are considerable better. Generalized Gradient Approximation (GGA) and LDA have been used to verify which one describe better the structural parameters and the electronic structure. We use the Siesta code, with GGA where the basis set is a combination of atomic orbitals. Our calculated lattice constants and band structure for the wurtzite ZnO give good results compared with the experimental ones. Although is largely observerd stacking faults (SF) in ZnO, there is not any theoretical calculation on that. In this work we calculated the formation energy for a SF in ZnO using a supercell of 108 atoms. The stacking sequence is a AaBbAaCcAaBb SF, and we includied the corresponding point defects in this SF. Our results indicate that both Zn and O vacancies in the presence of SF are more stable that the same vacancies in a bulk without a SF.