If there are two allowed transitions, then there are two linear regions in tauc's plot. So I want to ask the value of bandgap is decided by the first linear region(lower energy value) or the bandgap lies in the range decided by both linear regions.
Will the answer change if transition counts in the second linear region(with higher energy) are more?
Nitin Kumar
hi attach u .xy data and say about u material. i will check.
santanu
May be, you have a thin film with another bandgap? i.e you have two materials...
@shantanu result of tauc plot will be like as shown in figure. There are two linear regions marked with lines giving two values of lines. Please explain.
Nitin Kumar
I have added a chapter of my research work in that extensive details of my band gap narrowed material is given u can see.
which is
"Non-Classical Crystal Growth Recipe" using nanocrystalline ceria: a detailed review .
Page No-16: how to distinguish Tauc and Urbach Region
Page No-23: bandgap narrowed ceria (having two linear region like your data)
Page No-25: Photoluminescence spectroscopy (Validating Two band gap observation)
go through the Uv-Vis-spectroscopy section u can analyze u data. if u face further difficulty u need to send me u data. material name, how it was done(liquid medium(conc.), film form. etc)
which will help.
Regards
Santanu
Santanu Kumar Padhi
please explain bandgap narrowed ceria, I didn't get it.
Nitin Kumar
see chapter-3 in my RG profile..
Chapter "Non-Classical Crystal Growth Recipe" using nanocrystalline ...
Santanu Kumar Padhi
what I understand after reading that is your main peak is at 400nm(fast transitions) which contributes to bandgap value in tauc plot and transition at 510nm and 575nm(slow transition) contributes defects and results in narrowing the bandgap. Am I correct?
Dear Nitin Kumar
Please find this new article, two bandgap energies he got and he explains that properly.
Regards
maybe the references mentioned in https://www.researchgate.net/post/What_is_the_best_experimental_method_for_calculating_of_the_band_gap_of_a_semiconductor_material_what_is_it_based_on
can be of your help.
the explanation which I found and seems logical is in the link,
https://www.youtube.com/watch?v=P6Ioh6OunoU&t=392s
I do not understand very well about 2 linear regions. Is it of two materials or is it just one material?
All the semiconductors have two energy gaps, one direct and another indirect. One of them is much probable than the other. It is the statistic probability that gives the character to the material, direct or indirect bandgap semiconductor. From the point of view of the experiment, a direct gap is observed in thin samples whereas for the observation of the indirect gap thicker samples are needed.
The DRS or Absoprtion spectra using UV-VIS-NIR is used for the calculations which are going to be used in the determination of band gap using tauc plots. if you use the right transition type i.e. direct or indirect in the calculation you will get only one linear line in the tauc plot.
Nitin Kumar Tauc used an equation in 1968 to calculate the absorption edges (bandgaps) of amorphous Ge and Si from their absorption data.
(αhν)γ=A(hν-Eg)
In this equation, α is the absorption coefficient, h is Planck’s constant, υ is the frequency of the incident photon, A is a proportionality constant (which is determined by the index of refraction, electron, and hole effective masses; however, it is usually taken as 1 for amorphous materials), and Eg is the bandgap energy. The important term is the exponent γ, which denotes the nature of the electronic transition, that is, when γ=2 it is a direct allowed transition, and when it is equal to 1/2, it is an indirect allowed transition. For γ=2/3 it is a direct forbidden transition, and for γ=1/3 an indirect forbidden transition. Typically, the allowed transitions dominate the basic absorption processes, giving either direct or indirect transitions.
Thus, the basic procedure for a Tauc analysis is to acquire optical absorbance data for a sample in question that spans a range of energies from below the bandgap transition to above it.
Plotting the (αhν)γ versus (hν) is a matter of testing γ=2 or γ=1/2 to compare which provides the better fit and thus identifies the correct transition type.
I have provided the Template file (Origin file) in the video description. Thanks
https://youtu.be/LLESVSsZmlg
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