Magnesium Doping for the Promotion of Rutile Phase Formation in the Pulsed Laser Deposition of TiO₂ Thin Films

抄録

The preparation of a transparent and smooth rutile-type TiO₂ thin film without the use of the crystallographical effect of the substrate is a challenge for the advanced utilization of TiO₂ in the fields of optics and solid state ionics. Because acceptor doping leads to the formation of oxygen vacancies, this method has promise as a new approach to promote the formation of rutile-type TiO₂. Mg²⁺-doped TiO₂ thin films were prepared by pulsed laser deposition, and the effects of Mg²⁺ doping on the phases present, the microstructure, the optical properties, and the surface roughness of the films were investigated. Particular attention was paid to the Mg²⁺ distribution in the prepared films. The formation of the rutile phase was promoted by 2.7 mol% and 5.5 mol%Mg²⁺ doping. The negligible segregation of Mg²⁺ and absence of change in the extinction coefficient by Mg²⁺ doping indicate that Mg²⁺ worked as the acceptor and induced oxygen vacancies for charge compensation, which promoted the formation of the rutile phase. Given that Mg²⁺ is a doubly charged acceptor, Mg²⁺ doping is a more effective method for promoting the formation of the rutile phase than trivalence doping. Besides the excellent optical properties (n ≈ 3.03 and k < 0.02 at λ = 400 nm) of the 2.7%Mg²⁺-doped rutile-type TiO₂ thin film deposited at 350℃, the films were smooth, with a roughness index of only approximately 0.8 nm. This method of preparing smooth rutile-type TiO₂ thin films has potential for the further development of TiO₂-based resistive memory devices.