Transparent Conductive Properties of TiOx and Nb-Doped TiOx Films Produced by Reactive Co-Sputtering from Ti and Nb2O5 Targets

Abstract

We investigated the structural and transparent conductive properties of oxygen-deficient TiOx films that were deposited by metal-mode reactive electron cyclotron resonance plasma sputtering from a Ti target at 400 °C. Crystallites in a strongly reduced state (x≈1) had face centered cubic (fcc) structures with the resistivities ranging from 10-4 to 10-3 Ω cm, and the optical transmittance in the visible wavelength was between 25 and 55%. In a sufficiently oxidized state (x≈2), rutiles nucleated with resistivites higher than 10-2 Ω cm, and the optical transmittance was between 60 and 80%. The intermediate composition (1< x < 2) corresponded to fcc structures although the crystallinity approached an amorphous state with increasing x. Crystallization into magneli phases (TinO2n-1) was observed only for thick films at deposition temperatures higher than 500 °C. Carriers were n-type for rutile, but p-type for the fcc and magneli phases. Nb-doped TiOx films were produced by metal-mode sputtering of TiOx with co-sputtering Nb and O from an Nb2O5 target. The donor role of Nb5+ could be identified only in the oxidized rutile state, but the resistivity increased at higher Nb2O5 sputtering powers due to oxidation of Nb atoms that substituted Ti sites.