PN Junction Electric Field Profile

/ edmundsj
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How to calculate the electric field profile within the P/N Junction, as well as how to calculate the electric field and the depletion width, and how the band diagram of the PN junction arises from this.
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.

[@quinnzzillaa]

Thank you for this very logical explanation and color coding! I really appreciate that you draw the graphs directly below to show how you go from one representation to the next.

[@JordanEdmundsEECS]

Thanks :D

[@KineHjeldnes]

Thank you so much for these videos about pn junction. When my professor talked about this I couldn't understand one bit of what that energy diagram had of information. Now I completely get it!!!!

[@bkahraman99]

I want to thank you from the heart ! I was trying to understand this for a such a long time . Thank you so so much.

[@francescoturra4901]

I follow your videos from Italy! Thank you for very good contents and explanations!

[@hhsgzhz9096]

You’re a lifesaver .. thank you 💙💙💙💙💙💙💙

[@user-yy1op8vu4m]

This guy is crazy with his videos. THank you so much

[@farshidtavakoli6107]

Extraordinary explanation, thanks a lot

[@grizzleyeasy4480]

adding to bucketlist - get gauss laws tattoed on my arm xD

[@defn0tjake]

get all of Maxwell's equations tattooed on you

[@denis4429]

@Shane Jericho Fucking scammers leave this holy channel!

[@aymenbk9138]

I just saw someone in the comments say you're a lifesaver, and you know what? he's absolutely right

[@JordanEdmundsEECS]

🥰

[@oraange]

facts!

[@anandmodi6948]

Just amazing

[@akashdeeppaul9272]

Could you tell me why is the graph of the potential flipped over even though in both the cases the p-side and the n-side were same relative to each other ?

[@crystalcreator1024]

thanks for the video ,it helps a lot ! good good study ,day day up!

[@idaahmad8294]

Thank you for this very logical

[@claudius9512]

8:26 Is it correct that the energy is equal to -qV? Because now I am confused as according to electrostatics the energy is equal to +qV with q=+/-|e| depending on the carrier type.

[@omartusson]

Thank you very much.

[@mahmoudbiomy8281]

thanks doctor

[@surabee3398]

I was having an existential crisis before I came across your channel:'))

[@JordanEdmundsEECS]

Man I remember having an existential crisis in my device physics class too, glad you've been pulled back to the world of normal crises :)

[@yonatanj4]

thank you!!!

[@RenegadeFury]

at 8:00 how come the voltage doesn't go back down to 0? You said it stays high, but I'm not sure why

[@JordanEdmundsEECS]

Because you are integrating the electric field, which is always pointing in the same direction. It’s the same exact reason why when you have charge on two capacitor plates the voltage across them is nonzero.

[@Zaborovnik]

Good lecture! Have you tried to calculate the fields and potential without doping constant assumption, taking the concentration of p as a function of x? I solved it (probably wrong) by assuming that potential of the base counteracts the greatest chemical potential of an emitter, by solving that equation I get xp, and then I solve an equation of electrical fields, finding xn.

[@anaghapandharkar8024]

One doubt, is the net (effective) charge density at each point of the depletion layer zero??

[@JordanEdmundsEECS]

Nope, the charge density of any given slice of the depletion region is not zero, but if you add up all the charge in all the slices it will sum to zero.

[@susmithatalupula9791]

Why there is no net charge outside the junction

[@EagleLogic]

3:47 the subtle humor 🤣😂

[@hazarjaber2814]

At 3:38 why there’s no net charge outside the 2 regions you drew?

[@JordanEdmundsEECS]

Because if there was, the system would not be in equilibrium, and there would be a restoring force (an electric field) which drives the system to equilibrium (same charge on either side).

[@lucioaurelio2203]

why is E(x) the integral of the charge?

[@JordanEdmundsEECS]

Maria Thereza Great question! I believe I cover that in the prior video, you get that from integrating Gauss’ Law in 1D (which relates the derivative of the E-field to charge density).

[@zeinabh3397]

Thanks for the fantastic videos. As a chemist, I'm confused about one thing; how is electric field decreasing? I understand the electric field is at a maximum at the pn junction interface, because that's where you 'feel' the full positive and negative charge on either side of that interface and within the depletion region. So why isn't electric field increasing as you approach the interface from either side? Another thing about using the word 'decreasing'; an electric field can't be negative, right?

[@mgx9383]

Electric field is a vector, which means it has both magnitude and direction. Magnitude is always non-negative (this must be what you had in mind). Direction in this one-dimentional case can be (+) or (-). Here it is negative, because it's opposite of the direction of x axis (E is towards left from positive to negative ions, while x is towards right).

[@inonconczudcn]

2 mathematicians unliked the video

[@agnesagnes287]

should have a new tattoo on my arm haha

[@OfficialAnarchyz]

isn't energy W for work?

[@JordanEdmundsEECS]

Yes that’s an unfortunate conflict of notation >

[@carsongreenz]

Ill get it tattooed, only if @Jordan Edmunds says so.

[@MrTheRabber]

You computed the magnitude of the E field for the opposite direction wrt to the E arrow you draw

[@nizarch22]

3:18 I think you meant "the charge desnity is p as a function of x." You mixed up Q and p.

[@vidhanshujain2413]

I Tattooed it on my arm....😂😂😂

[@mdshadmanahmad2910]

I was looking for this comment XD

[@priyanksharma4178]

"I apologize to mathematicians watching this video" , Hahahahaha 4:20

[@percyvile]

"if you haven't memorised this by now you should get it tattoed on your arm" 😂

[@JordanEdmundsEECS]

I personally would suggest the memorization route... xD

[@justuschiang4710]

4:10 Why apologize! :) :) :)

[@mugiwara-no-luffy]

Noice

[@JordanEdmundsEECS]

memegenerator.net/img/instances/68375583/noice.jpg

[@yucel2378]

if you dont memorise that equation just have a tottoo done it on your arm! ahahaha

[@JordanEdmundsEECS]

XD

[@flyingbirds6794]

why did you apologized from mathematicians?😀

[@user-xr2pm3bp4q]

Rma😂