Abstract
We provide a first-principles description of the crystalline and oxygen-deficient Ta2O5 using refined computational methods and models. By performing calculations on a number of candidate structures, we determined the low-temperature phase and several stable oxygen vacancy configurations, which are notably different from the previous results. The most stable charge-neutral vacancy site induces a shallow level near the bottom of conduction band. Stability of different charge states is studied. Based on the results, we discuss the implications of the level structures on experiments,including the leakage current in Ta2O5-based electronic devices and catalysts.
Highlights
Tantalum pentoxide (Ta2O5) has attracted considerable attention in recent years due to its potential applications in the electronics industry[1,2] and catalysis.[3,4] The high dielectric constant of Ta2O55–12 puts it a candidate to substitute SiO2 in the conventional complementary metal–oxide– semiconductor (CMOS) devices
The oxygen vacancy plays a key role: It is considered a source of the leakage current in CMOS and a major reaction center in polymer electrolyte fuel cell (PEFC)
The role of oxygen vacancies in Ta2O5 is contrasting in CMOS and PEFC applications: The vacancy is the less the better for the former while the more the better for the latter
Summary
Tantalum pentoxide (Ta2O5) has attracted considerable attention in recent years due to its potential applications in the electronics industry[1,2] and catalysis.[3,4] The high dielectric constant of Ta2O55–12 puts it a candidate to substitute SiO2 in the conventional complementary metal–oxide– semiconductor (CMOS) devices. Density functional theory (DFT) calculations were applied to Ta2O5 on its structural, electronic and dielectric properties within the local density approximation (LDA) or generalized gradient approximation (GGA).[16,17,18,19] The works on oxygen-deficient Ta2O5 used some simplified crystalline models for the L-Ta2O5 phase to study the energy levels induced by the oxygen vacancies.[16,17] Recently, both β-Ta2O514 and δ-Ta2O515 were found meta-stable by phonon calculations,[18] and the L-Ta2O5 phase was found the most stable. Conventional DFT-LDA/GGA calculations by using hybrid functional for the exchange-correlation interactions, and the instability problem by using a crystal model without simplifying the unit cell of L-Ta2O5.13 We have investigated a number of vacancy sites and the associated level structures, which are found distinct from the previous reports. In procedure 2, they are optimized at the doubly positively charged state followed by re-optimization at the charge-neutral state
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