Is there any way to find out optical band gap and electrical band gap using simple instruments like UV-Vis spectrophotometer?
What are the parameters that influence the band gap in a metal thin film?
Can we calculate metal thin film thickness from absorbance spectrum?
(WRT silver thin film)
Dear Dr. Venkatesh Sri
Regards
Electrical band gap is simply the difference between the top of the valence band, and the bottom of the conduction band. For the optical band gap, you need to know where the higher energetic electrons are in the valence band, and determine the energy they need to reach the lowest energy level AVAILABLE on the conduction band. As you can expect, usually the higher energetic electrons on the valence band are the top of this band. But, for the lowest energy level AVAILABLE on the conduction band, the history is different. Depending on the doping level and the band structure, you fill the bottom of the conduction band until a limit. This filling of the lowest energy levels at the conduction band is a constant for your doping level. Thus, if you supply any external energy (electric field or ligth illumination mainly), the excited electrons that could reach an unoccupied level at the conduction band need an energy HIGHER than the electrical band gap, because of the already occupied levels due to doping. This is the so called OPTICAL BAND GAP (because of the main effect related to this phenomena is the hopping of electrons due to the illumination). And there is a lot of theory behind the behavior of the optical band gap, and here it is not the place to discuss about. Dear Sriram Subramanian, as you're working on a subject that I'm working on more than a 25 years ago, I'll be glad to discuss on it if you like. The same goes on to Chandra Shekhar Prajapati (I've see that you're working on ZnO thin films).
Thanks
It was copied from:
https://www.researchgate.net/post/Is_there_any_difference_between_electrical_band_gap_and_optical_band_gap/1
Silver is a metal and does not possess a fundamental band gap.
You would have to find the (real and imaginary) refractive index or dielectric function, determine tha absorbance from it and measure it on your specimens. Not trivial (since reflectance loss etc will depend on surface morphology of your film) but also not undoable. (There was a recent thread here on Ag on measuring thin film optical spectra (-> Ross Birney, https://www.researchgate.net/post/Reflectance_of_silver_in_infrared. you may find people with appropriate expertise there).
There are good "old" books on the optical properties of solids and metals (Abeles, 197x, Wooten, 198x) and also compilations of the optical properties, I guess.
Dear Dr. Venkatesh Sri
Regards
Electrical band gap is simply the difference between the top of the valence band, and the bottom of the conduction band. For the optical band gap, you need to know where the higher energetic electrons are in the valence band, and determine the energy they need to reach the lowest energy level AVAILABLE on the conduction band. As you can expect, usually the higher energetic electrons on the valence band are the top of this band. But, for the lowest energy level AVAILABLE on the conduction band, the history is different. Depending on the doping level and the band structure, you fill the bottom of the conduction band until a limit. This filling of the lowest energy levels at the conduction band is a constant for your doping level. Thus, if you supply any external energy (electric field or ligth illumination mainly), the excited electrons that could reach an unoccupied level at the conduction band need an energy HIGHER than the electrical band gap, because of the already occupied levels due to doping. This is the so called OPTICAL BAND GAP (because of the main effect related to this phenomena is the hopping of electrons due to the illumination). And there is a lot of theory behind the behavior of the optical band gap, and here it is not the place to discuss about. Dear Sriram Subramanian, as you're working on a subject that I'm working on more than a 25 years ago, I'll be glad to discuss on it if you like. The same goes on to Chandra Shekhar Prajapati (I've see that you're working on ZnO thin films).
Thanks
It was copied from:
https://www.researchgate.net/post/Is_there_any_difference_between_electrical_band_gap_and_optical_band_gap/1
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