First-principles study of carbon impurity effects in the pseudo-hexagonal Ta2O5

•Carbon-impurity effects on electronic structures of Ta2O5 are investigated.•Carbon atoms extend the defect state region in the bandgap.•The carbon preferentially located in the neighborhood of the oxygen vacancies.•The carbon impurities reduce the oxygen-vacancy formation energy.

Carbon-impurity effects on electronic structures and oxygen-vacancy formation stability of Ta2O5 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.