For Tauc Plot, (ahv)n/2 vs hv, from where do we get the value of absorption coefficient for that particular material. Is the value of absorbance same as absorption coefficient for solid samples ?
Can the %reflectance vs wavelength or the Kubelka Munk plot be used for determing the bandgap of the semiconductor in solid state.
Debashrita Sarkar
For solid powdered sample, calculating the band gap from Kubelka Munk plot (diffuse reflectance spectra) will be more authentic rather than from Tauc plot.
To find the band gap of the material from diffuse reflectance spectra, you need to calculate the Kubelka-Munk function, expressed as:
F(R) = (1-R)2 / 2R
Where: R is the absolute reflectance of the sample.Then to calculate the band gap:
- For the direct band gap material, you have to plot [F(R).hv]2 vs. hv. Where, hv is energy in eV. Then, the direct band gap energy, Eg, can be obtained by extrapolating the linear portion to [F(R).hv]2 = 0 in that graph.
- For the indirect band gap material, you have to plot [F(R).hv]1/2 vs. hv. Where, hv is energy in eV. Then, the indirect band gap energy, Eg, can be obtained by extrapolating the linear portion to [F(R).hv]1/2 = 0 in that graph.
I also attached a paper. You can go through this paper for details.
Best Regards,
Dipayan
Absorbance depends on the transmittance (A=-Log(T)) and absorption coefficient related by the following equation, absorption coefficient= A/ lambda. Alternatively, absorption coefficient can be calculated as following, absorption coefficient= ln[T/(1-R)^2]/ thickness of the sample.
following documents link might help you.
https://www.perkinelmer.com/labsolutions/resources/docs/APP_UVVISNIRMeasureBandGapEnergyValue.pdf
or Photoluminescence
https://iopscience.iop.org/article/10.1088/1757-899X/73/1/012120/pdf
@DipayanPal Thank you for your answer. The instrument in our department records the spectra in KM mode along with absorbance, transmittance and refectance. Can we plot the KM vs hv depending on direct or not or we have to convert the relectance into KM and then plot vs KM.
Debashrita Sarkar
You can directly plot KM data vs. energy (hv). No need to convert the reflectance into KM. If there is any confusion, you can contact me.
Regards,
Dipayan
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