An n-Type Transparent Conducting Oxide: Nb₁₂O₂₉

A Nb₁₂O₂₉ film is found to show transparent conducting properties with lowest resistivity of 3.3 × 10^–3 Ω·cm at room temperature. High transmittance (∼70% at wavelength of 435 nm and ∼50% at wavelength of 730 nm, 120 nm in thickness) in the visible is maintained with an optical band gap of ∼4.0 eV. The optical dielectric constant and effective mass were both larger than those for conventional transparent conducting oxides, leading Nb₁₂O₂₉ to exhibit high transparency. The n-type carrier density and Hall mobility at room temperature were 1.8 × 10²¹ cm^–3 and 0.8 cm² V^–1 s^–1, respectively. The origin of the charge carriers lies in the mixed-valent character of Nb, as revealed by photoemission measurements. This intrinsically doped d-electron-based transparent conducting oxide shows unique characteristics such as high refractive index and high-temperature stability, that is, maintaining high conductivity after annealing at 1000 °C in vacuum.