Considerations about the determination of optical bandgap from diffuse reflectance spectroscopy using the tauc plot

Abstract

The optical diffuse re ectance data of a semiconductor material is usually converted into the Kubelka-Munk function before proceeding to process the conventional Tauc's plot from which optical bandgap energy can be determined. Firstly, it is conventional/ customary to convert the percentage re ectance (R ∞ (%)) data which is obtained from UV-vis measurement into an equivalent re ectance (R ∞ ) that range between 0 and 1 before processing the Tauc's plot. Secondly, the Kubelka-Munk function is usually multiplied by the incident photon energy, hv, to produce an all-elements/ comprehensive Tauc's plot. Literature is scarce to convincingly demonstrate that a correct bandgap value can also be obtained from the Tauc's plot that is derived directly from the (R ∞ (%)) data without having to convert to R ∞ . Also, publication is rarely available to demonstrate that a correct bandgap value can be determined without having to multiply the Kubelka-Munk function by hv. Investigation shows diminutive differences in the bandgap values estimated from the R ∞ (%)-based Tauc's plots and the equivalent R ∞ -based Tauc's plots. This suggests that either of the methods can be employed for a proper bandgap estimate. Additionally, a comparison between the magnitude of the bandgap energies determined from the comprehensive Tauc's plot and when the Kubelka-Munk function is not multiplied by shows insigni cant differences in the estimated values. This suggests that either of the two methods can be used to obtain a reliable bandgap for direct and indirect optical gap semiconductors.

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“…UV–vis reflectance spectra were obtained using diffuse reflectance spectroscopy (DRS) to assess the absorption characteristics of ZnO across the electromagnetic spectrum and determine the band gap employing the Kubelka–Munk function . The theory allows for extracting quantitative information about semiconducting materials’ concentrations and optical properties by measuring a sample’s diffuse reflectance .…”