Why is the electric field zero outside of depletion region?

[pyctz]

why do electric field is zero out side of depletion region?

 

[mfb]

In an area with charge carriers, how could there be a permanent electric field without current flow?

 

[pyctz]

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?

 

[mfb]

This is simple U=RI with negligible I and finite R. The Coulomb rule is not useful here.

 

[pyctz]

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?

 

[mfb]

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.

 

[pyctz]

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?

 

[mfb]

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.

 

[pyctz]

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.

 

[mfb]

And that's exactly what you have outside the depletion region.

 

[pyctz]

And that's exactly what you have outside the depletion region.

but who cancel the field of depletion layer?

 

[mfb]

The other half of the depletion layer.

 

[pyctz]

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

 

[mfb]

Distance does not matter in a one-dimensional problem. Sheets of uniform charge density lead to uniform fields in all space (outside those sheets).

 

[pyctz]

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

 

[mfb]

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.

 

[pyctz]

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

 

[mfb]

Your statement in post 1 is an approximation.

Actually, every description you will ever see is an approximation. Just the quality is different.

 

[pyctz]

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.

 

[mfb]

- 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.

 

[pyctz]

- 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

 

[mfb]

Not exactly.
As I said, those statements are all approximations.

In the real world, physics is never exact.

 

[pyctz]

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

 

[pyctz]

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

 

[pyctz]

the answer of my thread is:
the free charges move until it becomes zero