1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Internel potentiel of PN junction? so complicated

  1. Dec 28, 2007 #1
    internel potentiel of PN junction?? so complicated

    homojunction PN (not polarized), externel potentiel difference applied = 0 Volt .

    i should demonstrate the equation: e*Vbi + Eg + ( Ec - Ef ) + ( Ef - Ev) = 0
    Given: Vbi= internel potential
    Eg= energy gap
    Ef = Fermi energy level
    Ec= Energy of conduction level
    Ev= Energy of valence level

    then i should deduce, that if the junction are so dopped that : Vbi = Eg/e
    ____________________________________________________________________________

    Ive try a lot to solve the first equation, but i couldnt find the solution. what ive found it that Vbi must equal Zero, and thats impossible cause .
    hope someone know how to solve that.
     
  2. jcsd
  3. Dec 29, 2007 #2
    homojunction PN- Need help

    Hi all, i need help in my little exercise
    a homojunction PN (not polarized), externel potentiel difference applied = 0 Volt .

    i should demonstrate the equation: e*Vbi + Eg + ( Ec - Ef ) + ( Ef - Ev) = 0
    Given: Vbi= internel potential
    Eg= energy gap
    Ef = Fermi energy level
    Ec= Energy of conduction level
    Ev= Energy of valence level

    then i should deduce, that if the junction are so dopped that : Vbi = Eg/e
    __________________________________________________ __________________________

    Ive try a lot to solve the first equation, but i couldnt find the solution. what ive found it that Vbi must equal Zero, and thats impossible cause .
    hope someone know how to solve that.
     
  4. Dec 29, 2007 #3

    Gokul43201

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    That equation looks wrong!

    Simply by inspection (draw the energy digram for the p-n junction), you should be able to see that:

    [tex]eV_{b} + (E_c - E_F) + (E_F - E_v) = E_g[/tex]

    I don't understand what you mean by this - it looks like an incomplete statement.
     
  5. Dec 29, 2007 #4
    its right, the equation is as you've write it:
    e*Vbi - Eg + ( Ec - Ef ) + ( Ef - Ev) = 0 there's a minus infront of Eg .
    but what i dont understand it, that if i draw the energy level diagram of the PN junction, i found that Eg = Ec - Ev and its the definition of Eg.
    if i write the statement like this: e*Vbi - Eg + Ec - Ef + Ef - Ev = 0 , then it will reduce to
    e*Vbi - Eg + Ec - Ev = 0, and as known Eg = Ec - Ev, so it should that Vb = 0.
    i really dont understand how to see by drawing the energy diagram for the PN junction that the realtion is right.
     
  6. Dec 29, 2007 #5

    Gokul43201

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    In the above equation Ec - Ef is measured in the n-type region and Ef - Ev is measured in the p-type region. This should be more explicitly stated in the equation.
     
  7. Dec 29, 2007 #6

    marcusl

    User Avatar
    Science Advisor
    Gold Member

    No. I think your statement of the problem is incorrect or missing some information. You probably mean Ec on one side of the junction and Ev on the other side, in which case Eg = Ec - Ev is not correct. Take a look at the energy diagram for the p-n in your text, or here

    http://ece-www.colorado.edu/~bart/book/book/chapter4/ch4_2.htm
     
  8. Dec 29, 2007 #7
    actualy what i dont understand thats the energy gap for a semiconductor is the difference betwen Ec and Ev. but , what will be the energy gap for a homojunction? and inside the barrier and outside. at left and right its the same?
    marcusl, ive chequed your link, the dont indicate that.
     
  9. Dec 29, 2007 #8
    10X to all. finally ive understand it. ive just drawn the energy junction diagram, and ive solved that. i think the problem that there's something missing in the equation, Ef-EVp , that's how it should be writen.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Internel potentiel of PN junction? so complicated
Loading...