Extraction of band gap energies and composition of mixed-phase polycrystalline semiconductors; a possible alternative method

Abstract The optical band gap energy, E g , of semiconductors is routinely determined using UV–Vis absorption measurements followed by Tauc‐plot analysis. This method requires knowledge of the Tauc exponent n , which corresponds to the nature of the electronic transition. While Tauc analysis is effective for single-phase semiconductors, it may not be applicable to mixed-phase materials that exhibit two different types of transitions. In this work, the absorbance of mixed-phase TiO 2 (anatase and rutile) with varying compositions is examined. Anatase has an indirect band gap ( n = 2), whereas rutile has a direct band gap ( n = ½). It is shown that the first derivative of the absorbance with respect to the wavelength, d A /d λ , yields phase-composition information largely similar to that obtained from XRD analysis. Furthermore, the positive peak of the second derivative, d 2 A /d λ 2 , provides a band-gap value that does not shift (within