Conductivity in transparent anatase TiO₂ films epitaxially grown by reactive sputtering deposition

The synthesis of semiconducting TiO₂ thin films deposited by reactive sputtering is discussed. In particular, defect doping of the anatase polymorph that is epitaxial stabilized on (0 0 1) LaAlO₃ was explored using either oxygen or water vapor as the oxidizing species. For films grown in oxygen, a transition from insulating to metallic conductivity of the films is observed as the O₂ pressure is reduced. X-ray diffraction measurements show the presence of the Ti_nO_2n-1 phase when the oxygen pressure is reduced sufficiently to induce conductive behavior. Hall measurements indicate that these materials are p-type. In contrast, the use of water vapor as the oxidizing species enabled the formation of n-type semiconducting TiO₂ with carrier density on the order of 10 ¹⁸ cm^-3 and mobility of 10-15 cm²/Vs.