PALS Measurements and Ab Initio/DFT Calculations for Positron Traps Identification on Zn-Based Nanopowders

GERMAN DARRIBA; LAURA C. DAMONTE; MARCOS MEYER; MARIO RENTERÍA

Lublin

Workshop; 12.5th International Workshop on Positron and Positronium Chemistry (PPC 12.5).; 2021

Positron annihilation lifetime spectroscopy (PALS) was applied to study different positron traps induced by mechanical work and doping with Al atoms in three different Zn-based semiconductors (ZnO, ZnSe and ZnTe). The experimental data werecomplemented by precise theoretical ab initio calculations in the framework of the Density Functional Theory (DFT). In this approach, the equilibrium structures of the doped systems (i.e., final atomic positions) were obtained applying the Full-Potential Augmented Plane Wave plus local orbitals (FP-APW + lo) method, embodied in the WIEN2k code. The Multigrid Instead of the K-spAce (MIKA) program was then used to predict the characteristic semiconductor lifetimes at theseequilibrium structures. Also, in order to evaluate the effects produced by the structural relaxations on the lifetime, we predict the annihilation lifetimes for the non-relaxed systems. With the aim to elucidate electronic distortions introduced by thedifferent defects (substitutional Al, Zn vacancies) in the semiconductor, the electronic density of states (DOS) was evaluated. The calculations predict that Al substitutes the Zn atom in the ZnO, ZnTe and ZnSe lattices and a zinc vacancy must appearin order to recover the semiconductor character, as suggest the experimental results. The characteristic positron annihilation lifetimes predicted for the doped samples are compared with those experimentally obtained. This combined experimental andtheoretical approach helps us to deeper understand the origin and characteristics of different positrons traps.