Evaluation of the Tauc method for optical absorption edge determination: ZnO thin films as a model system

Brian D. Viezbicke, Shane Patel, Benjamin E. Davis, Dunbar P. Birnie

Research output: Contribution to journalArticle

317 Citations (Scopus)

Abstract

One of the most frequently used methods for characterizing thin films is UV-Vis absorption. The near-edge region can be fitted to a simple expression in which the intercept gives the band-gap and the fitting exponent identifies the electronic transition as direct or indirect (see Tauc et al., Phys. Status Solidi 15, 627 (1966); these are often called "Tauc" plots). While the technique is powerful and simple, the accuracy of the fitted band-gap result is seldom stated or known. We tackle this question by refitting a large number of Tauc plots from the literature and look for trends. Nominally pure zinc oxide (ZnO) was chosen as a material with limited intrinsic deviation from stoichiometry and which has been widely studied. Our examination of the band gap values and their distribution leads to a discussion of some experimental factors that can bias the data and lead to either smaller or larger apparent values than would be expected. Finally, an easily evaluated figure-of-merit is defined that may help guide more accurate Tauc fitting. For samples with relatively sharper Tauc plot shapes, the population yields Eg(ZnO) as 3.276±0.033eV, in good agreement with data for single crystalline material.

Original languageEnglish
Pages (from-to)1700-1710
Number of pages11
JournalPhysica Status Solidi (B) Basic Research
Volume252
Issue number8
DOIs
Publication statusPublished - Aug 1 2015

Keywords

  • Band gaps
  • Near-edge absorptivity ratio
  • Optical absorption
  • Polycrystalline semiconductors
  • Tauc plots
  • Thin films
  • ZnO

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics

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