Evaluation of the Tauc method for optical absorption edge determination: ZnO thin films as a model system (Phys. Status Solidi B 8/2015)

Abstract

ZnO was used by Viezbicke et al. (pp. http://doi.wiley.com/10.1002/pssb.201552007) for assessing the accuracy of the Tauc method for band‐gap determination. This method is based on optical absorption data: longer wavelengths are barely absorbed, but wavelengths shorter than the band‐gap cut‐off are absorbed progressively more strongly, as illustrated schematically for three particular photon energies (upper left). These photons excite gradually wider direct transitions within the material's electronic structure (upper right) yielding larger absorption coefficient values. Direct‐gap materials like ZnO show a linear region in the (αhν)2 vs. Ephoton plot, which is extrapolated back to the x‐axis to find the threshold band‐gap value (lower right). Viezbicke et al. examined a large population of these bandgap determinations leading to an improved understanding of the accuracy of the method. Finally, an easily‐evaluated figure‐of‐merit was defined that may help guide more accurate Tauc fitting in the future. For samples with relatively sharper Tauc plot shapes the data found Eg(ZnO) to be 3.276 ± 0.033 eV, in good agreement with data for single crystalline material (lower left).

Physico-chemical characterization, Hirshfeld surface analysis and opto-electric properties of a new hybrid material: Tris (2-amino-5-chloropyridinium) hexachlorobismuthate(III)

“…The evaluated band gap of our compound was found to be 3.2 eV according to the Tauc plot method(see Fig. 9.b)which indicates that the crystal can have dielectric behavior to induce polarization when powerfulradiation is incident on the material [33].This value was obtained from the formula: (αhν) 1/n =A(hν-E g ) with n =1/2 for direct allowed transitions, where h is Planck's constant, n is the photon's frequency, α is the absorption coefficient, Eg is the band gap, and A is a proportionality constant [34].…”

Core Levels, Band Alignments, and Valence-Band States in CuSbS2 for Solar Cell Applications

“…Nevertheless, the direct and indirect band gaps of the CuSbS2 sample were determined from the absorption spectra both at room and cryogenic temperatures 70,71 , shown in the Tauc plots in Figure 7. Room temperature measurements (300 K) allow the extraction of both the direct (1.60 eV) and indirect (1.55 eV) band gaps, which are in agreement with a previous study, finding the direct transition to lie within 0.1 eV higher than the indirect transition, leading to previous misclassification of the fundamental gap of this material to be direct in nature 7 .…”

Synthesis, Optical, Chemical and Thermal Characterizations of PMMA-PS/CeO2 Nanoparticles Thin Film

“…The high energy region ( nm is where transmittance starts to decay to a vanishing value. This region contains the absorption edge [ 46 ] that is red-shifted upon increasing the concentration of Ce NPs in the polymeric matrix suggesting a significant reduction of optical band gap energy of (PMMA-PS)/CeO 2 nanocomposite thin films [ 47 ]. The incorporation of CeO 2 NPs into polymeric matrix leads to a compression of the host matrix.…”