Why is the electric field zero outside of depletion region?

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Discussion Overview

The discussion revolves around the behavior of the electric field outside the depletion region in semiconductor physics, exploring the underlying principles and mechanisms that lead to a zero electric field in that area. Participants engage in technical reasoning, challenge each other's claims, and explore the implications of charge distributions and approximations in the context of semiconductor devices.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants question why the electric field is zero outside the depletion region, seeking clarification on the role of charge carriers.
  • Others argue that the Coulomb rule is not applicable in this context, suggesting that the relationship between voltage, resistance, and current is more relevant.
  • There are claims that the remaining atoms in a doped semiconductor do not generate an electric field, leading to confusion about how the field from the depletion layer is canceled.
  • Some participants assert that the overall charge density remains zero even with the presence of free charges, which complicates the understanding of electric fields in the region.
  • There is a discussion about the nature of charge distribution and how it leads to uniform electric fields, with some emphasizing that distance does not matter in one-dimensional problems.
  • Participants highlight that the infinite sheet approximation is useful in many cases, although some argue that it does not hold in specific scenarios involving semiconductor dimensions.
  • Several contributions emphasize that all descriptions of electric fields and charge distributions are approximations, with some insisting that in ideal conditions, the electric field is exactly zero inside a conductor.
  • One participant concludes that free charges will move until the electric field becomes zero, although this statement is met with skepticism regarding its absolute accuracy.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the behavior of electric fields in the depletion region and outside of it. There is no consensus on the applicability of approximations or the exact nature of charge distributions and their effects on the electric field.

Contextual Notes

Limitations include the dependence on idealized models and approximations, as well as the complexity introduced by real-world semiconductor structures that may not conform to simplified theoretical descriptions.

pyctz
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why do electric field is zero out side of depletion region?
 
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In an area with charge carriers, how could there be a permanent electric field without current flow?
 
mfb said:
In an area with charge carriers, how could there be a permanent electric field without current flow?
can you explain it with using of coulomb rule?
 
This is simple U=RI with negligible I and finite R. The Coulomb rule is not useful here.
 
mfb said:
This is simple U=RI with negligible I and finite R. The Coulomb rule is not useful here.
in depletion layer there are uncovered charges that generate electric field , how cancel their field?
 
The remaining atoms have a charge as well. There is nothing "uncovered". A doped semiconductor has free charges of one type with zero overall charge density. If you remove those free charges the volume gets charged.
 
mfb said:
The remaining atoms have a charge as well. There is nothing "uncovered". A doped semiconductor has free charges of one type with zero overall charge density. If you remove those free charges the volume gets charged.
the remaining atom don't generate any fied, then who cancel the field of depletion layer?
 
pyctz said:
the remaining atom don't generate any fied
Sure they do.
Replace a silicon atom with boron. It has one electron and one proton less, so the overall charge is zero - but now you have a hole because another electron can bind there easily. If you fill the hole you have a negative charge.
Replace a silicon atom with phosphorus. It fits in the crystal structure but has a 5th valence electron, while the overall charge is still zero - but now you have an electron that will easily leave its spot. If you remove the free electron you have a positive charge.
 
mfb said:
Sure they do.
Replace a silicon atom with boron. It has one electron and one proton less, so the overall charge is zero .
if for each atom the overall charge is zero, then they don't generate any fied.
 
  • #10
And that's exactly what you have outside the depletion region.
 
  • #11
mfb said:
And that's exactly what you have outside the depletion region.
but who cancel the field of depletion layer?
 
  • #12
The other half of the depletion layer.
 
  • #13
mfb said:
The other half of the depletion layer.
it is not correct,
the other half is more far
then it can not cancel the field of opposite half
 
  • #14
Distance does not matter in a one-dimensional problem. Sheets of uniform charge density lead to uniform fields in all space (outside those sheets).
 
  • #15
mfb said:
Distance does not matter in a one-dimensional problem. Sheets of uniform charge density lead to uniform fields in all space (outside those sheets).
sheets of uniform charge must have infinite dimension(infinite plane) to lead uniform fields
in pn junction there is not infinite sheet
then distance matter
 
  • #16
Compare the typical thickness of a depletion region with the typical dimension of a semiconductor device.
The infinite sheet is a good approximation unless you consider modern microprocessors, and then things are much more complicated anyway.
 
  • #17
mfb said:
Compare the typical thickness of a depletion region with the typical dimension of a semiconductor device.
The infinite sheet is a good approximation unless you consider modern microprocessors, and then things are much more complicated anyway.
i don't talk about approximation
i talk about exact situation
 
  • #18
Your statement in post 1 is an approximation.

Actually, every description you will ever see is an approximation. Just the quality is different.
 
  • #19
mfb said:
Your statement in post 1 is an approximation.

Actually, every description you will ever see is an approximation. Just the quality is different.
actually, in non ideal diode electric field is zero outside of depletion region.
this is exact not approximation.
 
  • #20
- The electric field is never exactly zero anywhere.
- Charge distribution is never exactly uniform in space
- the depletion layer does not have an exact boundary
- ...
All approximations.
 
  • #21
mfb said:
- The electric field is never exactly zero anywhere.
- Charge distribution is never exactly uniform in space
- the depletion layer does not have an exact boundary
- ...
All approximations.
inside a conductor The electric field is exactly zero
 
  • #22
Not exactly.
As I said, those statements are all approximations.

In the real world, physics is never exact.
 
  • #23
mfb said:
Not exactly.
As I said, those statements are all approximations.

In the real world, physics is never exact.
if The electric field is not zero the free charges move until it becomes zero
 
  • #24
mfb said:
Not exactly.
As I said, those statements are all approximations.

In the real world, physics is never exact.
if The electric field is not zero the free charges move until it becomes zero
 
  • #25
the answer of my thread is:
the free charges move until it becomes zero
 

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