Analysis of defects in In2O3:H synthesized in presence of water vapor and hydrogen gas mixture

Abstract

Using hybrid functional-based density functional theory calculations, we analyze the structure and kinetics of defects formed in two competing synthesis routes to prepare hydrogen-doped In2O3 films, using a hydrogen and oxygen gas mixture vs synthesis in the presence of water vapor. For both of these synthesis routes, we find that H+ is the dominant defect species: when the Fermi level is close to the conduction band, H+ has a lower formation energy than other intrinsic or extrinsic defects. Our results also suggest that water molecules spontaneously split into H+ (which occupies octahedral voids) and OH− interstitials (which occupies vacant oxygen lattice sites or oxygen vacancies). From the analysis of the binding energies between these different defects, we conclude that these defects do not cluster and are most likely to stay spatially distributed throughout the films. In addition, the sum of formation energies of an oxygen (i.e., Oi2−) and a H+ interstitial is close to the formation energy of a OH− interstitial, meaning that water molecules are completely split into 2H+ and Oi2− at the synthesis conditions. Further, in the presence of H2 + O2 gas mixture, oxygen interstitials occupy oxygen vacancies while hydrogen interstitials occupy vacant oxygen lattice sites and form bonds with lattice oxygens. Our analysis of the defect equilibria suggests that the hydrogen content in films synthesized in the presence of water vapor is higher than films synthesized in the presence of a hydrogen gas mixture. At high dopant concentrations, a hydrogen bond network is formed in the system and this leads to large distortions in the lattice.