What is the difference between the so called Optical Bandgap and the Electrical Bandgap? Are there other kinds of Bandgaps?
Is in every case the same Gap energy between the highest occupied level in the valence band and the lowest occupied level in the conduction band, and just depending on the experimental method you use to determine it, is how it will be called; Optical bandagp, electrical bandgap, etc... ?
Or there are fundamental differences?
I hope someone can help me clarify to this since it has been confusing for me since I started into the topic.
If it depends on the case... I'm interesting in PbS thin films.
Best Regards! :)
For a pure single crystalline material, the energy band is parabolic and there is available energy state in between conduction and valance band. The energy gap between top of valence band and bottom of conduction band is electronic bandgap. However, if the material is amorphous and or composed with nanocrystal phase, there is a band tail and even defect state may be present in between conduction and valance band. If these materials will exposed with light, photons gets absorbed due to transition of electrons from band to band, band tail to band and even band to defect state, etc. So, for application of these materials in optical system needs a overall effective bandgap to quantify it's optical property , i.e. optical bandgap. This optical bandgap could be estimated using popular Tauc plot.
Please correct in 1st line " ..... There is no available energy state....." ....
Dear Franklin,
Many amorphous materials can be called semiconductors in the sense that they are
neither good conductors nor good insulators, but instead are poor conductors. Many are also similar to their crystalline counterparts in that they possess an optical gap. The reason for this general behavior seems to be that, even though the amorphous structure is quite random over long distances, there still seems to be considerable short–range order with local bonding requirements generally satisfied.
Please see the following discussion
https://www.researchgate.net/post/What_is_the_basic_difference_between_optical_band_gap_and_electrical_band_gap
Regards
Yes, I think it depends on the technique of finding it, but in the end the value will be same.
I have theoretical work with DFT calculation for this topic.
regards
The band gap of semiconductor is the same but determination is different . For example if it is determined by absorption spectroscopy it is Optical Band gap and if it is determined by electrical conductivity it is called thermal band gap.
In inorganic materials the optical band gap is equal to transport (electrical) band gap. Whereas for organic materials, the transport band gap (Et) excess the optical energy gap (Eg) due to the presence Exciton energy (Eex)
so we can conclude that : Et = Eg for inorganic materials
Et - Eg = Eex for organic materials
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