Idealizing Tauc Plot for Accurate Bandgap Determination of Semiconductor with UV-Vis: A Case Study for Cubic Boron Arsenide

TL;DR

This paper introduces a baseline removal method for UV-Vis Tauc plots to improve the accuracy of semiconductor bandgap determination, demonstrated on cubic boron arsenide and verified experimentally.

Contribution

It proposes a novel baseline correction technique for Tauc plots, addressing inaccuracies caused by baseline absorption in bandgap measurements.

Findings

Baseline removal improves bandgap accuracy.

Method converges previous discrepancies in c-BAs bandgap values.

Applicable to both direct and indirect bandgap semiconductors.

Abstract

The Tauc plot method is widely used to determine the bandgap of semiconductors via UV-visible optical spectroscopy due to its simplicity and perceived accuracy. However, the actual Tauc plot often exhibits significant baseline absorption below the expected bandgap, leading to discrepancies in the calculated bandgap depending on whether the linear fit is extrapolated to zero or non-zero baseline. In this study, we show that both extrapolation methods can produce significant errors by simulating Tauc plots with varying levels of baseline absorption. To address this issue, we propose a new method that involves idealizing the absorption spectrum by removing its baseline before constructing the Tauc plot. Experimental verification of this method using a gallium phosphide (GaP) wafer with intentionally introduced baseline absorptions shows promising results. Furthermore, we apply this new method to cubic boron arsenide (c-BAs) and resolve discrepancies in c-BAs bandgap values reported by different groups, obtaining a converging bandgap of 1.835 eV based on both previous and new transmission spectra. The method is applicable to both indirect and direct bandgap semiconductors, regardless of whether the absorption spectrum is measured via transmission or diffuse reflectance, will become essential to obtain accurate values of their bandgaps.