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Evaluation of the Tauc method for optical absorption edge determination: ZnO thin films as a model system
Author(s) -
Viezbicke Brian D.,
Patel Shane,
Davis Benjamin E.,
Birnie Dunbar P.
Publication year - 2015
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.201552007
Subject(s) - band gap , absorption edge , materials science , enhanced data rates for gsm evolution , stoichiometry , figure of merit , plot (graphics) , thin film , absorption (acoustics) , analytical chemistry (journal) , optics , condensed matter physics , mineralogy , chemistry , mathematics , statistics , physics , nanotechnology , computer science , optoelectronics , organic chemistry , telecommunications , chromatography
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 E g (ZnO) as 3.276 ± 0.033 eV, in good agreement with data for single crystalline material.