Structural and electronic properties of Al-doped ZnO semiconductor nanopowders: Interplay between XRD and PALS experiments and first-principles/DFT modeling

Abstract

A combined experimental and novel theoretical ab initio structural and electronic study was performed in order to characterize ZnO semiconductor nanopowders doped with Al atoms. For this, powder mixtures of ZnO and metallic Al in adequate proportions yielding different contents of Al (5, 10, and 30 at. %) were prepared by mechanical milling. The systems were characterized by X-ray diffraction and positron annihilation lifetime spectroscopy measurements. Additionally, combining two first-principles methods based on the Density Functional Theory (DFT) we calculated the final equilibrium structures for different concentrations of Al dopants and Zn vacancies in ZnO, predicting afterwards the characteristic positron annihilation lifetimes at these equilibrium structures. In addition to the structural relaxations, the ab initio predictions of the electronic properties in the studied systems help us to understand deeper the origin and characteristics of different positrons traps. This experimental and ab initio/DFT combined study allows to verify the dopant incorporation into the ZnO wurtzite structure and to extract the maximum information from the experimental data, giving an insight into the different defect complexes and their influence in the structural and electrical properties.