The effect of Nb substitution on synthesis and photo-response of TiO 2 thin films prepared by direct current magnetron sputtering

Paul A. Desario, Michael E. Graham, Ryan M. Gelfand, Kimberly A. Gray

Research output: Contribution to journalArticle

8 Scopus citations

Abstract

TiO2 has a limited photoefficiency for solar energy harvesting and conversion due to its large bandgap. Nb substitution into the TiO 2 lattice was investigated to red-shift its photoresponse by introducing defect energy levels in the host bandgap. Ti1-xNb yO2 thin films (0 ≥ y ≤ 0.52) were prepared by direct current reactive magnetron sputtering. The effect of Nb concentration on crystal phase formation and subsequent change in optical and electronic properties were determined. Films had an increasing rutile proportion as Nb concentration increased, and all films prepared for y > 0.25 were pure rutile. Nb substituted as Nb(V) or a mixture of Nb(IV)/(V) while Ti remained Ti(IV). Therefore, in these materials cation vacancies formed to electronically compensate for group V doping. Nb-doped rutile films showed no red-shift in optical response while Nb-doped anatase/rutile composites were strongly red-shifted. Photocurrent measurements were made to determine if the enhanced visible light absorption generated mobile electron-hole pairs or was due to localized excitations at color centers. At low Nb concentrations (∼ 2 at.%), visible light absorption generated mobile charge carriers, while at higher concentrations (> 9 at.%), no mobile charge carriers were created. At higher Nb concentrations, the formation of mobile charge carriers was hindered by charge recombination at cation vacancies.

Original languageEnglish (US)
Pages (from-to)3562-3568
Number of pages7
JournalThin Solid Films
Volume519
Issue number11
DOIs
StatePublished - Mar 31 2011

Keywords

  • Doped oxides
  • Niobium
  • Sputtering
  • Titanium oxide
  • Visible light response
  • X-ray diffraction
  • X-ray photoelectron spectroscopy

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Surfaces and Interfaces
  • Surfaces, Coatings and Films
  • Metals and Alloys
  • Materials Chemistry

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