Quasi-Fermi Levels Explained

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Quasi-Fermi levels allow us to extend the idea of the Fermi energy to non-equilibrium conditions when the original concept of a single Fermi energy breaks down. It is a fundamental and heavily-used concept in optoelectronics when you almost never operate at or near equilibrium.

This is part of my series on semiconductor physics (often called Electronics 1 at university). This is based on the book Semiconductor Physics and Devices by Donald Neamen, as well as the EECS 170A/174 courses taught at UC Irvine.

Hope you found this video helpful, please post in the comments below anything I can do to improve future videos, or suggestions you have for future videos.

[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.

[vintoncerf]

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

[michaelquinatoa]

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

[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?

[sainikomal]

Hey...why is Efn going towards didn't understand this part....?

Plz Provide brief explanation

[theillusionzone]

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

[manojkumarjana]

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

[pentachronic]

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.