Welcome to the P-n Junction Inquiry

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SUMMARY

The discussion centers on the characteristics of the electric field in a p-n junction, specifically addressing the behavior of the depletion region. Participants clarify that the depletion region behaves like a dipole, with the electric field being negative inside and positive outside, albeit with a small magnitude. The conversation emphasizes that while the depletion region is not infinite, the approximation of infinite sheets of charge can be useful for understanding the electric field behavior in transistors. The consensus is that the electric field is zero outside regions with net charge, leading to a constant potential.

PREREQUISITES
  • Understanding of p-n junctions in semiconductor physics
  • Familiarity with electric fields and dipole behavior
  • Knowledge of charge distribution in semiconductor materials
  • Basic principles of transistor operation
NEXT STEPS
  • Study the electric field distribution in p-n junctions using simulation tools like COMSOL Multiphysics
  • Explore the concept of depletion regions in detail through resources on semiconductor physics
  • Learn about the approximation of infinite charge sheets and its applications in electronics
  • Investigate the role of electric fields in the operation of various types of transistors
USEFUL FOR

Students and professionals in electrical engineering, semiconductor physicists, and anyone involved in the design and analysis of electronic components, particularly those focusing on p-n junctions and transistors.

daudaudaudau
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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 ??
 
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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.
 

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