Positron Annihilation Lifetime Spectroscopy (PALS) experiments and first-principles/DFT modeling on nanostructured semiconductors

L. C. DAMONTE; M. MEYER; G. N. DARRIBA; M. RENTERÍA

Nara

Conferencia; HYPERFINE 2023 - International Conference on Hyperfine Interactions and their Applications; 2023

HFI Executive Committee

A combined experimental and novel theoretical ab initio structural and electronic study was performed to characterize Zn-based semiconductor nanopowders doped with Al atoms. Doped II-VI semiconductors (ZnM; M=O, Se and Te) were obtained by mechanical milling from mixtures containing Al2O3 or metallic Al in adequate proportions yielding contents of 5, 10, and 30 at.% Al. Positron annihilation lifetime spectroscopy measurements confirmed the original Zn-based polycrystalline structure that is maintained for all milling times and the progressive substitutional incorporation of Al atoms into the semiconductor matrix. PALS spectroscopy also allowed to identify the defects induced by mechanical work. Additionally, combining two first-principles methods based on the Density Functional Theory (DFT) the final equilibrium structures for different concentrations of Al dopants and Zn vacancies in all samples were calculated, predicting afterwards the characteristic positron annihilation lifetimes at these equilibrium structures. A slight shift on the energy band gap with respect to pure semiconductor was revealed from optical diffuse reflectance measurements for all studied samples. The ab initio predictions of the electronic structure in the studied systems give an insight into the different defect complexes and their influence on the structural, optical, and electrical properties. It is also stated that a Zn vacancy must appear to recover the semiconductor character, as suggest the experimental results. This theoretical approach helps us to deeper understand the origin and characteristics of different positrons traps