The structures and electronic properties of Ta2O5 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 Ta2O5 over δ‐ and β‐Ta2O5 and metastable relative to other recently proposed structures. Its diffraction spectrum and bandgap energy are in good agreement with experimental data. Therefore, the pseudo‐hexagonal structure might form in polycrystalline films and affect the switching process of resistive memory devices. Moreover, a neutral oxygen vacancy is found to induce an occupied defect state at 2.5 eV above the top of the valence band, in agreement with X‐ray photoelectron spectroscopy results. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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Carbon-impurity effects on electronic structures and oxygen-vacancy formation stability of Ta 2 O 5 resistive memories are investigated using the density-functional theory. Generalized gradient approximation with on-site Coulomb corrections is employed for the investigation. The unintentionally incorporated carbon can cause unwanted increase in the resistive off-state leakage current by extending the defect state region in the bandgap. The carbon impurities are found to be preferentially located in the neighborhood of the oxygen vacancies, and they reduce the oxygen-vacancy formation energy, which is predicted to have an influence on lowering the forming voltage.