Welcome to the P-n Junction Inquiry

Click For Summary

Discussion Overview

The discussion revolves around the characteristics and behavior of the electric field in a p-n junction, particularly in relation to the depletion region and its representation in diagrams. Participants explore the implications of the electric field's direction and magnitude, as well as the nature of the depletion region.

Discussion Character

  • Debate/contested
  • Technical explanation

Main Points Raised

  • One participant questions the accuracy of a figure depicting the p-n junction, suggesting that the electric field should be positive outside the depletion region, leading to a voltage approaching zero at infinity.
  • Another participant asserts that the figure is correct but does not provide a detailed explanation, prompting requests for clarification.
  • A participant describes the depletion region as a dipole, referencing an external image to illustrate their point about the electric field being negative inside the dipole and positive outside, albeit with a small magnitude.
  • In response, another participant argues against the dipole analogy, stating that the configuration resembles two infinite sheets of charge, which would produce a constant electric field outside the sheets.
  • One participant counters that the depletion region is not infinite and that the electric field depicted in the questioned figure is not constant, challenging the previous assertion about the nature of the field.
  • A later reply emphasizes that the approximation of infinite sheets is valid for many transistors and clarifies that the electric field is zero outside regions with net charge, leading to a constant potential.

Areas of Agreement / Disagreement

Participants express differing views on the representation of the electric field in the p-n junction, with no consensus reached regarding the accuracy of the figure or the nature of the depletion region.

Contextual Notes

Participants note limitations in their arguments, such as the assumptions about the extent of the depletion region and the behavior of the electric field in different regions of the junction.

daudaudaudau
Messages
297
Reaction score
0
Hello.

I have a question regarding the p-n junction. When I look at figure B here:

http://en.wikipedia.org/wiki/P-n_junction

it looks completely wrong to me. Take the E-field. It is going to be positive outside the depletion region, which in turn will make the voltage tend towards zero for x→±∞. Right ??
 
Physics news on Phys.org
The figure looks good.
daudaudaudau said:
It is going to be positive outside the depletion region
No.
(explain more what you don't understand to get more specific answers)
 
mfb said:
The figure looks good.
No.
(explain more what you don't understand to get more specific answers)

Well the depletion region is a dipole, isn't it? So the e-field will look like this

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/imgele/edip2.gif

So if the field is negative "inside" the dipole, it is positive outside (but of small magnitude, of course).
 
daudaudaudau said:
Well the depletion region is a dipole, isn't it? So the e-field will look like this

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/imgele/edip2.gif
It is not, you have two "infinite" sheets, and infinite sheets have a constant field around them - two sheets with opposite charge of the same magnitude lead to fields that cancel everywhere outside.
 
mfb said:
It is not, you have two "infinite" sheets, and infinite sheets have a constant field around them - two sheets with opposite charge of the same magnitude lead to fields that cancel everywhere outside.

Well, clearly the depletion region is not infinite in extent. Also, the field is not constant in the figure that you said looks good.
 
daudaudaudau said:
Well, clearly the depletion region is not infinite in extent.
That is a very good approximation for most transistors.
Also, the field is not constant in the figure that you said looks good.
The field is zero outside the regions with net charge, so the potential is constant. The field is not constant in the region with net charge, as there is net charge on the sides.
 

Similar threads

  • · Replies 7 ·
Replies
7
Views
4K
  • · Replies 2 ·
Replies
2
Views
3K
Replies
3
Views
2K
  • · Replies 2 ·
Replies
2
Views
3K
  • · Replies 4 ·
Replies
4
Views
3K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 2 ·
Replies
2
Views
4K
  • · Replies 4 ·
Replies
4
Views
4K
  • · Replies 1 ·
Replies
1
Views
3K
  • · Replies 7 ·
Replies
7
Views
3K