Hydrogen in Ag-doped ZnO: theoretical calculations

TL;DR

This study uses density functional theory to explore how hydrogen interacts with silver-doped ZnO, revealing stable complexes, migration behaviors, and vibrational properties that impact the material's electronic characteristics.

Contribution

It provides detailed theoretical insights into hydrogen behavior in Ag-doped ZnO, including site preferences, migration barriers, and vibrational modes, which were previously not well understood.

Findings

Hydrogen can form stable Ag-H complexes in ZnO.

H migration to Ag sites has energy barriers of 0.3 - 1.0 eV.

Ag-H complexes can negatively affect p-type conductivity.

Abstract

Based on density functional theory calculations, we systematically investigate the behaviors of a H atom in Ag-doped ZnO, involving the preference sites, diffusion behaviors, the electronic structures and vibrational properties. We find that a H atom can migrate to the doped Ag to form a Ag-H complex by overcoming energy barriers of 0.3 - 1.0 eV. The lowest-energy site for H location is the bond center of a Ag-O in the basal plane. Moreover, H can migrate between this site and its equivalent sites with energy cost of less than 0.5 eV. In contrast, dissociation of such a Ag-H complex needs energy of about 1.1 - 1.3 eV. This implies that the Ag-H complexes can commonly exist in the Ag-doped ZnO, which have a negative effect on the desirable p-type carrier concentrations of Ag-doped ZnO. In addition, based on the frozen phonon calculation, the vibrational properties of ZnO with a Ag-H complex are predicted. Some new vibrational modes associated with the Ag-H complex present in the vibrational spectrum of the system.