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 language | English |
---|---|
Pages (from-to) | 1700-1710 |
Number of pages | 11 |
Journal | Physica Status Solidi (B) Basic Research |
Volume | 252 |
Issue number | 8 |
DOIs | |
Publication status | Published - 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