A mechanism of defect creation in amorphous Ta2O5

Defect creation mechanisms in amorphous (a)-Ta2O5 films employed in various microelectronics applications, e.g. resistive switching memories, are still poorly understood. Addressing this issue, our Density Functional Theory (DFT) calculations demonstrate that electrons and holes can be trapped in bipolaron states at structural precursor sites in a-Ta2O5. Such carriers trapping significantly reduces average energies for the formation of Frenkel pairs (FPs) of oxygen vacancies and interstitial oxygen ions to about 1.0 eV for hole trapping and 3.4 eV for electron trapping. The average diffusion barriers of the O interstitials are 0.3 eV for O2- and 1.4 eV for O0, which forms a bond with a neighbouring O ion at the site. However, the low recombination barriers of FPs complicate the kinetics of the creation of stable defect pairs, suggesting that the degradation and breakdown of Ta2O5 cannot be explained by trapping of holes alone and additional factors, including the presence of pre-existing O vacancies, grain boundaries, and other defects, should also be taken into account.