Evidence summary
Evidence summary
Use a Tauc analysis only when the optical quantity and material assumptions support it. Convert the measured transmission, absorption or diffuse reflectance with an appropriate model, test plausible transition exponents, disclose the selected linear region and report the result as an apparent optical gap with sensitivity to fitting choices.
Key takeaways
- 01Absorbance is not automatically the absorption coefficient α.
- 02Diffuse reflectance requires an explicit scattering model such as a justified Kubelka–Munk treatment.
- 03The transition exponent is a physical assumption, not a visual preference.
- 04Report fit-window sensitivity and avoid excessive decimal precision.
Identify the measured optical quantity
Transmission through a film, absorbance in a cuvette and diffuse reflectance from a powder require different routes to an absorption-like quantity. Record thickness, reference, path length and scattering context.
- Do not relabel absorbance as α without justification.
- Correct substrate or blank contributions.
- Inspect interference fringes and saturation.
Treat the exponent as a model choice
A direct or indirect transition assumption changes the transformed ordinate. Compare physically plausible models and explain the choice from electronic structure or prior evidence, not from whichever plot looks straightest.
- State the exponent convention.
- Keep photon-energy units explicit.
- Avoid automated model selection from R² alone.
Make the fitted region reproducible
Show the chosen points on the Tauc plot and test nearby windows. A stable intercept across defensible windows is more informative than one high regression score.
- Report the fit interval.
- Include confidence or sensitivity bounds.
- Label the result as apparent when assumptions are incomplete.
Use corroborating evidence
Compare the optical edge with PL, composition, structure and theory where available. Agreement across techniques strengthens an interpretation; disagreement can reveal defects, excitons or model failure.
Methodology and scope
This guide uses the original Tauc framework and later methodological critiques to separate data conversion, transition assumptions and regression. It does not claim that every semiconductor obeys a simple Tauc relation.
Limitations
- Tauc analysis was developed for particular electronic-transition models and is often overextended.
- Thickness, scattering, interference and sub-gap absorption can dominate the apparent edge.
- Multiple linear-looking regions can produce different intercepts.
- The optical gap may differ from a fundamental quasiparticle gap.
References
- [1]
Optical properties and electronic structure of amorphous Ge and Si
Tauc, Grigorovici and Vancu. Physica Status Solidi B (1966).
doi:10.1002/pssb.19660150224 ↗ - [2]
How to correctly determine the band gap energy of modified semiconductor photocatalysts based on UV–Vis spectra
Makuła, Pacia and Macyk. Journal of Physical Chemistry Letters (2018).
doi:10.1021/acs.jpclett.8b02892 ↗
Suggested citation
Suggested citation
SciPhys Research Team. “Tauc Plot Band Gap Analysis.” SciPhys, August 5, 2026. https://www.sciphys.com/blog/tauc-plot-band-gap-analysis
Apply the workflow
Build a reviewable Tauc analysis from your spectrum.
Upload UV–Vis data with the technique preselected and keep conversion, exponent and fit range attached to the result.