Nb doped SrTiO₃: Effect of oxygen content on the doping mechanism
C.F. Chang1*, Q.Y. Chen1,7, P.V. Wadekar1,7,2, O. Lozano3, M.S. Wong4, W.C. Hsieh1, Y.S. Wang1, Y.T. Lin1, H.H. Liu1, C.W. Chang1, H.W. Seo5, H.H. Liao6, W.K. Chu7, H.C. Huang8
1Department of Physics, National Sun Yat-Sen University, Kaohsiung, Taiwan
2Department of Chemistry, University of Liverpool, Liverpool, United Kingdom
3Department of Physics, University of Namur, Namur, Belgium
4Department of Material Science and Engineering, National Dong-Hua University, Hua-Lien, Taiwan
5Dept. of Physics and Astronomy, University of Arkansas, Little Rock, United States of America
6Enli Technology, Kaohsiung Science Park, Kaohsiung, Taiwan
7Dept. of Physics and Texas Center for Superconductivity, University of Houston, Houston, United States of America
8Department of Material Science and Engineering, National Sun Yat-Sen University, Kaohsiung, Taiwan
* presenting author:張淳富, email:richang65@gmail.com
SrTiO₃ is known for double-doping, by which free carriers are created via cation substitution and oxygen vacancies, a case reported in literature being La:SrTiO3-δ. In an effort to attain transparent oxide conductors. we have investigated this phenomenon Nb:SrTiO₃, thinking that Nb would have more valence electrons to contribute to conduction carriers. The Nb-doped SrTiO3 thin films were grown under different oxygen partial pressures to control the oxygen stoichiometry. Compositional analysis of the metal elements was done by proton-induced X-ray emission (PIXE) and X-ray photoelectron spectroscopy (XPS) techniques, while structural properties were analyzed by X-ray diffraction (XRD). Transport measurements show that the conductivity is much more strongly dependent on the oxygen partial pressures than the level of Nb doping. This disparity arises because of the formation of multivalent Nb dopants, the makeup of which largely depending on the deposition and post-annealing conditions. The interplays between the doping levels and associated atomic defects in the host material is essential to the understanding and ultimately the ability of tuning the electrical and optical properties for transparent-conductor applications.

Keywords: SrTiO3, Nb, activation energy, doping, lattice constant