Atomic and electronic structures of intrinsic defects in Ta$_2$O$_5$: ab initio simulation

The atomic and electronic structure of intrinsic point defects in orthorhombic tantalum oxide has been studied by numerical simulation within the density functional theory. It has been shown that all defects responsible for metal enrichment of Ta$_2$O$_5$ serve as electron and hole traps. Under conditions of strong oxygen depletion and at a metal-insulator interface, which are characteristic of resistive memory elements, interstitial tantalum atoms compete with an oxygen vacancy in the formation of a conducting filament. Interstitial oxygen atoms are not involved in charge transport. Tantalum substituting oxygen can be considered as a combination of the oxygen vacancy and interstitial tantalum. The analysis of the calculated thermal and optical energies of trap ionization shows that the oxygen vacancy is a key defect for charge transport in Ta$_2$O$_5$.