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

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 ± 0.033 eV, in good agreement with data for single crystalline material.

Tuning of material properties of ZnO thin films grown by plasma-enhanced atomic layer deposition at room temperature

“…It is modeled by fit parameters controlling the amplitude, broadening, center energy, left and right endpoints, and left and right midwidth control points. 40 The bandgap energy was obtained by extrapolating the linear part from a ðahÞ 2 vs h plot to intersect the energy axis (Tauc-plot), 41 in which a is the absorption coefficient, h is Planck's constant, and is the photon's frequency. The absorption coefficient a was calculated from the measured extinction coefficient k using a ¼ 4pk=k.…”

“…5(c)] for an RF-power of 30 W shows a smooth transition and k only slowly decays toward higher wavelength, i.e., there is a significant absorption above the bandgap, indicating the existence of defect absorption states (e.g., carbon impurities, O-H groups, or oxygen vacancies, as shown in the XPS analysis). 41 For higher RF-powers, the onset of the absorption becomes sharper pointing out a reduced defect concentration and less absorption at higher wavelengths. For the sample grown with 30 W, the absorption coefficient a is 405.0 and 42.1 cm À1 at a wavelength of 633 and 1000 nm, respectively.…”

Synthesis and Characterization of an Efficient Hole-Conductor Free Halide Perovskite CH3NH3PbI3Semiconductor Absorber Based Photovoltaic Device for IOT

“…whether the transition is allowed or forbidden and whether it is direct or indirect: n = 2 for an indirect allowed transition; n = 3 for an indirect forbidden transition; n = 1/2 for a direct allowed transition; n = 3/2 for a direct forbidden transition. 32 In case the participation of a phonon is not necessary to conserve the momentum, the transition is direct (allowed) while in case of direct (forbidden) transition, a small but finite contribution of the phonon is considered. Indirect transitions occur when at least one phonon participates in the absorption or emission of one photon to conserve the momentum.…”

Enhanced Red Emission in Ultrasound-Assisted Sol-Gel Derived ZnO/PMMA Nanocomposite

“…), where α, hv, and B are the absorption coefficient, photon energy, and constant, respectively [26]. PL spectra of ZnO NPs shown in Figure 3(c) exhibit two distinct UV and visible emission regions.…”