Considerations About the Determination of Optical Bandgap from Diffuse Reflectance Spectroscopy Using the Tauc Plot

The optical diffuse reflectance 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 reflectance (R_∞(%)) data which is obtained from UV-vis measurement into an equivalent reflectance (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 \(hv\) shows insignificant 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.