Origins of Electronic Band Gap Reduction in Cr/N Codoped TiO2

Luca Gavioli, Mirco Chiodi, C. Parks Cheney, P. Vilmercati, E. W. Martin, M. Regmi, G. Eres, T. A. Callcott, H. H. Weitering, N. Mannella

Research output: Contribution to journalArticlepeer-review

42 Citations (Scopus)

Abstract

Recent studies indicated that noncompensated cation-anion codoping of wide-band-gap oxide semiconductors such as anatase TiO2 significantly reduces the optical band gap and thus strongly enhances the absorption of visible light [W. Zhu et al., Phys. Rev. Lett. 103, 226401 (2009)]. We used soft x-ray spectroscopy to fully determine the location and nature of the impurity levels responsible for the extraordinarily large (similar to 1 eV) band gap reduction of noncompensated codoped rutile TiO2. It is shown that Cr/N codoping strongly enhances the substitutional N content, compared to single element doping. The band gap reduction is due to the formation of Cr 3d(3) levels in the lower half of the gap while the conduction band minimum is comprised of localized Cr 3d and delocalized N 2p states. Band gap reduction and carrier delocalization are critical elements for efficient light-to-current conversion in oxide semiconductors. These findings thus raise the prospect of using codoped oxide semiconductors with specifically engineered electronic properties in a variety of photovoltaic and photocatalytic applications.
Original languageEnglish
Pages (from-to)36404-36408
Number of pages5
JournalPhysical Review Letters
Volume112
DOIs
Publication statusPublished - 2014

Keywords

  • CHARGE-TRANSFER
  • OXIDATION
  • OXIDE
  • RESONANT PHOTOEMISSION
  • RUTILE
  • SPECTROSCOPY
  • SURFACE
  • THIN-FILMS
  • VISIBLE-LIGHT
  • X-RAY-ABSORPTION

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