I have synthesized plasma polymerized thin films. From UV-Vis data, I have calculated direct and indirect band gap using Tauc relation.
Is it possible to observe both kinds of band gap in a material simultaneously?
I want to know a correct explanation.
In fact most of the materials possess direct and indirect transition, either allowed or forbidden. Normally indirect transition is prevalent in most semiconductors, particularly amorphous compounds, and direct transition normally characterizes the crystalline materials. There is a method for determining the type and number of optical transitions that can occur in the studied samples.
Dear Azeez Abdullah Barzinjy Thanks for your explanation. But still, I am not clear. I wanted to know that a material can possess both kinds of bandgap simultaneously.
You have also mentioned that there is a method for determining the type of transition. could you please tell me, what is that method? Is it PL spectroscopy?
Dear Md. Mahmud Hasan,
This question is well studied in semiconductors theoretically and experimentally as well:
Yes, a material can have both direct and indirect band gap. If the absorption coefficient of a material rapidly increase with increase photon energy, the band energy, is called direct band gap energy.
How do you know a material has either direct or indirect bandgap energy?
The minimum energy gap is the difference in energy between the conduction band-edge and the valence band edge. If both the band edges are at the same k-point of the Brillouin zone, the band gap is direct. If these differ by a finite wave vector, the band gap is indirect.
How can I determine whether a semiconductor is direct band gap or ...
https://www.researchgate.net/publication/329926491_Unified_theory_of_direct_or_indirect_band-gap_nature_of_conventional_semiconductors
How do you know if a band gap is direct or indirect?
If the k-vectors are different, the material has an "indirect gap". The band gap is called "direct" if the crystal momentum of electrons and holes is the same in both the conduction band and the valence band; an electron can directly emit a photon.
Direct and indirect band gaps - Wikipedia
https://en.wikipedia.org/wiki/Direct_and_indirect_band_gaps
Dear Len Leonid Mizrah
Thank you for your excellent explanation.
I have another question: is a material can be operative as radiative or non-radiative, simultaneously?
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