1. Limited time only! Sign up for a free 30min personal 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!

Homework Help: Questions about the Potential and E-Field directions of P-N junction

  1. Sep 24, 2012 #1

    Hi, on re-visiting some basic ideas about PN junctions, I found I am confused with the depletion region diagram:

    I understand that the depletion region originated from the diffusion current at the local contact of the p and n type material, the electrons diffuse from the n type to p type building a local E-Field, the field intensity is the strongest at the contact interface and decreases gradually towards the end of the material of both p and n type materials.

    1. From the diagram above, why is the potential of the material remains a negative(towards the end of p-type) and positive(towards the n-type)?
    Isn't it only the depletion region that will encounter a change in potential?
    How come the whole right and whole left are positive and negative after all?:confused:

    2. As the +ve ions are left at the right(n side) and -ve ions are created on the left(p side), I suppose the E-field points from the right to left(n to p), the arrow indicates this and makes sense.
    However, from the E-Field graph, the intensity is a negative value, does it mean they are actually taking "right" as positive?

    Thanks for reading:biggrin:
  2. jcsd
  3. Sep 24, 2012 #2

    rude man

    User Avatar
    Homework Helper
    Gold Member

    1. E points to the -x direction so E(x) is negative.

    2. Since the electric field is the (negative) derivative of V wrt x, then V integrates to a constant once E = 0.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook