First-Principles Study of Oxygen Vacancy and Hydrogen Impurity Effects in the Pseudo-hexagonal Ta_2O_5

摘要

The structures and electronic properties of Ta_2O_5 polymorphs were calculated using density-functional theory employing the generalized gradient approximation with on-site Coulomb corrections. Using this approach, a pseudo-hexagonal structure was found to be a stable polymorph of Ta_2O_5 over the δ- and β-Ta_2O_5 and is proposed as a new candidate structure which might be formed during the resistive switching process in random access memory devices. Its diffraction spectrum is shown to successfully match the recently indexed experimental structure and its band-gap energy is also in good agreement with available experimental data. A neutral oxygen vacancy is shown to induce an occupied defect state at 2.5 eV above the top of the valence band, as also found by x-ray photoelectron spectroscopy spectrum measurement. Furthermore, the effects of the hydrogen impurity on the electronic structures were investigated.