Dielectric Response of Ta2O5, Nb2O5, and NbTaO5 from First-Principles Investigations.

HighK dielectrics are intensively investigated as a replacement for SiO₂ in integrated nanoelectronics. In particular, for the next generation of dynamic random access memory metalinsulatormetal capacitors, the Ta and Nbbased oxides are among the most interesting candidates that display a relatively large dielectric constant with a bandgap larger than 3 eV. In this paper, we show that it is possible to modulate the dielectric response of Ta₂O₅ by admixing it with Nb₂O₅. The dynamical charges and dielectric constants of Ta₂O₅ and Nb₂O₅ for different crystal phases were calculated at the density functional theory level. The averaged dielectric constants range between 27 (38) and 42 (77) for Ta₂O₅ (Nb₂O₅) in the hexagonal and orthorhombic varieties. A mixed orthorhombic NbTaO₅ composition exhibits a directionally averaged dielectric constant of 54, close to the arithmetic mean value of the binary species. The origins of the dielectric permeability are discussed and compared to experimental measurements. [ABSTRACT FROM AUTHOR]