Metallicity in Ultra-Thin Oxygen-Deficient SrTiO${}_3$ Thin Films

Abstract

We report on the observation of metallic behavior in thin films of oxygen-deficient SrTiO${}_3$ - down to 9 unit cells - when coherently strained on (001) SrTiO${}_3$ or DyScO${}_3$-buffered (001) SrTiO${}_3$ substrates. These films have carrier concentrations of up to 2$\times 10^{22}$ cm${}^{-3}$ and mobilities of up to 19,000 cm${}^2$/V-s at 2 K. There exists a non-conducting layer in our SrTiO${}_{3-\delta }$ films that is larger in films with lower carrier concentrations. This non-conducting layer can be attributed to a surface depletion layer due to a Fermi level pinning potential. The depletion width, transport, and structural properties are not greatly affected by the insertion of a DyScO${}_3$ buffer between the SrTiO${}_3$ film and SrTiO${}_3$ substrate.

5 pages, 4 figures