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

Abstract

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 (${R}_{\infty }$(%)) data, which is obtained from UV-vis measurement into an equivalent reflectance (${R}_{\infty }$) 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, alternatively be obtained from the Tauc’s plot that is derived directly from the (${R}_{\infty }$(%) data without having to convert to ${R}_{\infty }$. Also, publication is rarely available to demonstrate that a proper bandgap value can be determined without having to multiply the Kubelka–Munk function by the term $hv$. The present investigation shows diminutive differences in the bandgap values estimated from the ${R}_{\infty }$(%)-based Tauc’s plots and the equivalent ${R}_{\infty }$-based Tauc’s plots. This suggests that either of the methods can be employed for a precise bandgap estimate. A comparison between the magnitudes of the bandgap energies determined from the comprehensive Tauc’s plot and when the Kubelka–Munk function is not multiplied by $hv$ reveals insignificant differences in the estimated values. This suggests that either of the two methods can be employed to obtain a reliable bandgap for direct and indirect optical gap semiconductors.