Idealizing Tauc Plot for Accurate Bandgap Determination of Semiconductor with Ultraviolet-Visible Spectroscopy: A Case Study for Cubic Boron Arsenide

The Tauc plot is widely used to determine the bandgapof semiconductors,but the actual plot often exhibits significant baseline absorptionbelow the expected bandgap, leading to bandgap discrepancies fromtwo different extrapolations. In this work, we first discuss the originof baseline absorption and show that both extrapolation methods canproduce significant errors by simulating Tauc plots with varying levelsof baseline absorption. We then propose and experimentally verifya new method that idealizes the absorption spectrum by removing itsbaseline before constructing the Tauc plot. Finally, we apply thisnew method to cubic boron arsenide (c-BAs), resolve its bandgap discrepancies,and obtain a converging bandgap of 1.835 eV based on both previousand new transmission spectra. The method is applicable to both indirectand direct bandgap semiconductors with absorption spectrum measuredvia transmission or diffuse reflectance, which will become essentialto obtain accurate values of their bandgaps.