Analysis of correlation between electrical and infrared optical properties of anatase Nb doped TiO2 films

Optical and electrical analysis are required to clarify infrared reflection behavior of anatase Nb doped TiO2 (NTO) films, a novel transparent conductive oxide (TCO). In this paper, UV–vis-near infrared transmission spectrum, Fourier transformed infrared (FTIR) reflection and ellipsometry analysis are conducted on anatase NTO films (Nb doping concentration: 6, 4 and 2 at%) deposited by pulse laser deposition (PLD). NTO samples show good transparency from 400 nm to 1000 nm, but no obvious plasmon induced high IR reflection even when wavelength >3000 nm. Assuming inhomogeneous resistivity (ρ) and mean scattering time (τ) along film thickness, dielectric constants (εr, εi) and optical constants (n, k) are extracted by fitting spectroscopic ellipsometry using Code-Lorentz (CL) & Drude exponential model. It is shown that unique optical constants and small τ (1.1–2.6 fs) intrinsically prevent NTO to be high infrared reflective TCO.