Quasi-Fermi Levels Explained

[@oraange]

To sum up , Quasi-fermi energy is the splitting of Fermi energy when the equilibrium condition is broken ( excess of carrier concentration).

[@ArsenedeBienne]

the unit of optical generation rate is cm-3*s-1. you need to multiply it by the carrier lifetime (tau~1e-6-1e-5 in Si) to obtain a steady state carrier concentration in the zero order approximation.

[@vintoncerf7562]

im a grad student from germany, and i watch your videos to pass my advanced optoelectronics class xD

[@elhambaghestani7643]

Amazing explanation. Thanks

[@aliabdolahzadehziabari9101]

Very useful and expressive

[@mounikakare]

Great explanation

[@theillusionzone]

4:48

[@mahmoudbiomy8281]

thanks doctor

[@michaelquinatoa139]

There is a mistake in the Quasi Fermi level equations. I think it should not be dividing by 'q'

[@sagarksahoo4667]

Well it is not wrong, dividing by q would give the result in volts(v), although we mostly use eV.

[@dr.sanjeet]

@@sagarksahoo4667 right

[@ЭйвейлАлександр]

@@sagarksahoo4667 Well explained, dude! I've learnt

[@jyotiradityasatpathy3546]

They are using q as 1, which lets you easily switch between eV and V for energy and potential difference respectively.

[@danielpetka446]

@@sagarksahoo4667 right but he is calculating the energy difference - which has to be eV not V

[@coolwinder]

What is Fermi-level, why do we use it and why does it get flat across pn junction, is it a coincidence or is there deeper maning?

[@nthyagarajan27]

Fermi level is like a reference used to explain electron and hole population. It's not a coincidence that it's flat in equilibrium. kzbin.info/www/bejne/fXy6kHmjYsp7n7M Refer to this video, I have the details explained here

[@theillusionzone]

I am one of your patrons, what is a quasi-Fermi level (in simple English)?

[@GodzillaGoesGaga]

Here you go I had the same question. kzbin.info/www/bejne/paXWZq2ul9efi80

[@sainikomal281]

Hey...why is Efn going towards Efp.......I didn't understand this part....? Plz Provide brief explanation

[@manojkumarjana]

what's the intrinsic concentration (ni) you assumed to get hole concentration?

[@tcaddesk746]

intrinsic concentration usually for silicon is 1.5e10/cm3, he used ni^2/Nd to calculate hole concentration.

[@GodzillaGoesGaga]

Hi Jordan, I'm following your videos and I am still having an issue in understanding what the Fermi Level represents. I see papers talking about the sea of particles and the Fermi level represents this. I am not clear at all and this is bugging the crap out of me because it's ruining my understanding of band diagrams. Could you explain or point me to a video that explains this in more layman's terms. Is is just representing the donor concentration average energy level and I'm over thinking it ? Love your vids and your teaching style BTW.

[@GodzillaGoesGaga]

So thinking about this I have an analogy. Imagine a swimming pool (let's call it N-type). The average water level is the Fermi level (the system has energy in the form of water). Now there will be ripples and spray that gets onto the sides of the pool but typically the water level is just below the lip of the pool. The water that makes it over the lip is effectively thermal energy. Now imagine a big blob of a diver (a hole). This diver gets onto a diving board (potential energy) and jumps (kinetic energy). The hole hits the surface and an electron (water N-Type) gets splashed out to the side and is free to move around. The hole sinks to the bottom and is absorbed. Would this analogy be a good representation ??

[@jordanedmunds4460]

​@@GodzillaGoesGaga Seems like a pretty reasonable analogy to me. The only deficit is that the fermi level is often located within the bandgap, where the density of states is zero. So you don't *actually* have any electrons near the fermi energy. But if there *were* states there, they would almost all be filled (strictly speaking, they would all be filled at T=0K), and then extra electrons (which happen to have higher thermal energy) would be 'splashing' at the edges of the pool.

[@GodzillaGoesGaga]

@@jordanedmunds4460 Thank you Jordan. SomI've actually found a really good video that has clarified this for me conceptually. kzbin.info/www/bejne/paXWZq2ul9efi80

[@henrynwosu6277]

"the fermi level is powerful" yet not one definition. you are teaching physics be more precise thank you. In all your calculations, how can you skip something so Important as stating what a fermi Level Is. You just said it is located somewhere between the conduction and valence bands. Is that a definition?

[@RagingAcid]

this isnt hockey

[@jasonkuku8155]

Not following what you explained