Accurate determination of the band gap energy of non-translucent semiconductor materials through the Tauc method: Theoretical framework, limitations, technical hints, and automated algorithms

The Tauc method remains a widely used procedure for determining the band gap energy ( E g ) of semiconductor materials. However, analysts should be aware of its limitations and primary sources of uncertainty. In addition, misconceptions and the use of alternative graphical methods without physical foundations can lead analysts to obtain meaningless results. This study addresses the basic theory, technical aspects, challenges, and computational achievements related to the Tauc method. Its reliability was studied in determining the E g of pristine and mixed oxides. The E g of pure samples was determined consistently (ZnO: 3.25 ± 0.0 eV; CdO: 2.08 ± 0.02 eV), whereas underestimated values were found for mixed samples (Δ E g ≤ 0.07 eV). The possible origin of this effect is discussed. It is shown that the accuracy of the conventional Tauc method can be improved by considering a baseline function. A new automated Tauc algorithm based on the baseline approach is proposed. It demonstrates high accuracy (≤0.05 eV) and speed (0.04 s per spectrum), being able to analyze spectra with multiple absorption edges ∼0.8 eV apart. Although this study focuses on non-translucent samples, such as powders and opaque coatings, the central concepts and procedures can be adapted to analyze other types of samples. • Practical guide for determining the band gap energy of non-translucent materials. • The limitations and sources of uncertainty of the Tauc method are addressed. • Incorporating a baseline improves the accuracy of the conventional Tauc analysis. • A new automated Tauc algorithm with high accuracy and speed is proposed.