Physics Asked by Aleksejus Pacalovas on December 26, 2020
Many sources I’ve seen have alluded to:
An exciton can form when a material absorbs a photon of higher energy than its bandgap
I looked at absorption enhancing effects of excitons, and am aware of the Hydrogenic series for an exciton. It seems to me that the absorption of light energy below the bandgap is due to exciton formation.
Image 1 represents the absorption spectra of a semiconductor at low Temperature (excitons can form)
Image 2 is a schematic representation that I have drawn based on my understanding
My understanding in reference to Direct bandgap semiconductors:
ex
1. When I supply the material with a photon of energy equal to ħω = Eg – Eex
1 , the material will absorb this photon and this energy will go into creating an exciton that has a quantum number n = 1.ex
2 ), n = 3 (using photon energy of ħω = Eg – Eex
3 ) and so on (Image 2).I drew Image 2 based on my understanding so it may not be the correct representation.
My Question – Is the statement "An exciton can form when a material absorbs a photon of higher energy than its bandgap" hence incorrect? Would a better explanation be –
An exciton can form when a material absorbs a photon of lower energy
than its bandgap. This can be seen in image 1 where we get
characteristic lines such as n = 1 describing the formation of
excitons.
I've discussed the nature of exciton a few days ago in response to your other question. So, applying what is said there to what you ask now: Excitons can form when semiconductors are illuminated at sub-gap energies - as the spectra that you have shown demonstrate. They can also form when the photon energy is above the band gap, in which case the electron and the hole have to lose some energy to get to the bound excitonic state (to phonons, via electron-electron collisions, etc.)
So yes, the statement that you are referring to is unprecise. Unfortunately, this rather simple nature of excitons is systematically misrepresented.
Answered by Vadim on December 26, 2020
Get help from others!
Recent Questions
Recent Answers
© 2024 TransWikia.com. All rights reserved. Sites we Love: PCI Database, UKBizDB, Menu Kuliner, Sharing RPP