TiO2-based transparent conducting oxides; the search for optimum electrical conductivity using a combinatorial approach

Abstract

A series of Nb, W, N and F:TiO₂ thin-film systems were grown by a combinatorial atmospheric pressure chemical vapour deposition (APCVD) process. Conditions were varied in each experiment to produce a series of films with compositional gradient. For each system, the electrical resistivity at a number of positions (up to 200 on each film) was screened using a high-throughput tool. This allowed easy identification of the material with the lowest electrical resistivity across a reservoir of combinatorially produced samples. The most conductive material within each system was analysed in depth by X-ray photoelectron spectroscopy, wavelength dispersive X-ray analysis, X-ray diffraction, Raman spectroscopy, scanning electron microscopy, UV-visible-NIR spectroscopy and Hall effect measurements. The most electrically conductive materials are found in the F:TiO₂ [F_s ≈ 4–5%, ρ = 0.21 Ω cm, μ = 3.6 cm² V⁻¹ s⁻¹, n = 8.1 × 10¹⁸ cm⁻³] and Nb:TiO₂ [Nb = 0.07 ± 0.03%, ρ = 0.22 Ω cm, μ = 3.4 cm² V⁻¹ s⁻¹, n = 8.3 × 10¹⁸ cm⁻³] systems. The electrical resistivities reported for Nb:TiO₂ and W:TiO₂ are the best to date for materials grown by APCVD. Extensive comparisons with the literature are made and summarised in this report.