Formation of highly-conductive SrTiO$_{3-\delta }$ by pulsed laser deposition of TiO$_{2}$ on SrTiO$_{3}$ substrate

We report on formation of highly conductive SrTiO$_{3-\delta }$ by pulsed laser deposition of TiO$_{2}$ on SrTiO$_{3}$ substrate under relatively reducing atmosphere. Anatase TiO$_{2}$ thin films were grown on SrTiO$_{3}$(001) and (LaAlO$_{3})_{0.3}$(Sr$_{2}$AlTaO$_{6})_{0.7}$ (LSAT)(001), for comparison, by pulsed laser deposition under oxygen pressure of $P$o$_{2 }$= 5x10$^{-8}$ Torr. In-situ RHEED (reflection high energy electron diffraction) measurements during film deposition revealed a clear streak pattern of 4x1 reconstruction, indicating growth of high quality anatase (001) films. Meanwhile, the anatase (001) films deposited on LSAT with thickness of $>$2 nm showed spotty RHEED patterns, indicating formation of oxygen-poor TiO$_{2-x}$. These facts lead us to a conclusion that oxygen atoms in SrTiO$_{3}$ substrate diffuse into anatase TiO$_{2}$ during the film growth process. In the TiO$_{2}$/SrTiO$_{3- \delta }$ heterostructure, we observed high mobility of 1x10$^{4}$ cm$^{2}$/Vs (5K) and Shubnikov-de Haas oscillation (0.5K), proving formation of clean SrTiO$_{3- \delta }$ without structural deformation.