An n-Type Transparent Conducting Oxide: Nb12O29

A Nb12O29 film is found to show transparent conducting properties with lowest resistivity of 3.3 x 10(-3) Omega.cm at room temperature. High transmittance (similar to 70% at wavelength of 435 nm and similar to 50% at wavelength of 730 nm, 120 nm in thickness) in the visible is maintained with an optical band gap of similar to 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 x 10(21) cm(-3) and 0.8 cm(2) 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 degrees C in vacuum.