What Happens When Two Different Donor Concentrations Meet in a Junction?

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Discussion Overview

The discussion centers on the behavior of a junction formed by two n-type semiconductor regions with different donor concentrations (Nd=1016 and Nd=1015). Participants explore the implications of this configuration, including electron diffusion and the expected band diagram characteristics.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants propose that there would be electron diffusion from the higher donor concentration side to the lower concentration side.
  • One participant suggests that there will be slight band bending due to an electric field created by the difference in donor concentrations.
  • Another participant questions whether the described junction behaves like a Schottky diode, indicating that the band diagram would show discontinuities due to the differing doping levels.
  • There is a suggestion that the band bending would be more pronounced on one side of the junction compared to the other, depending on the doping levels.
  • A later reply challenges the initial assumptions, asserting that the junction behaves like a Schottky diode and describing the expected band diagram behavior.

Areas of Agreement / Disagreement

Participants express differing views on the nature of the junction and the corresponding band diagram. While some agree on the presence of band bending and electron diffusion, there is contention regarding the classification of the junction and the specifics of the band diagram.

Contextual Notes

Participants have not fully resolved the implications of the junction's behavior, and there are assumptions regarding the nature of the junction that remain unaddressed.

snoothie
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Hi,

If we had two junctions one side with Nd=1016 & another side with Nd=1015 put together.

What happens in such a junction? Would we see electron diffusion from the high donor concentration side to the lower concentration side? What should the band diagram of the junction look like?

Does anyone have a link to any resources discussing about this online?
Thanks.
 
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If you have an nn junction, all you have is a big lump of n-type material.
 
snoothie said:
Hi,

If we had two junctions one side with Nd=1016 & another side with Nd=1015 put together.

What happens in such a junction? Would we see electron diffusion from the high donor concentration side to the lower concentration side? What should the band diagram of the junction look like?

Does anyone have a link to any resources discussing about this online?
Thanks.

What do you think the band diagram would look like?
 
berkeman said:
What do you think the band diagram would look like?

think there will be a slight band bending due to a efield between the nn junctions which is due to the difference in donor concentrations? (gradient of 10^16 - 10^15 / x0 - x1)? then due to the field there should be some drifting of electrons from the n junction with higher nd concentration to the n junction with lower nd concentration?

not sure if I'm on the right track...
 
snoothie said:
think there will be a slight band bending due to a efield between the nn junctions which is due to the difference in donor concentrations? (gradient of 10^16 - 10^15 / x0 - x1)? then due to the field there should be some drifting of electrons from the n junction with higher nd concentration to the n junction with lower nd concentration?

not sure if I'm on the right track...

No you are not.
This would be a Schottky diode. And there would be a electron sheet just at the metalergical junction. So the bend diagram would be discontinuous as it would both decrease on the left and right part of the juctions but on the left part it decreases rapidly while the right part decreases gently. As a result, the end point of the left part would be much lower than the start point of the right part.

Assume the right part got highly doped.
 
thanks for correcting.

So you are saying a nn junction = schottky diode, and the band bending should be like what we see for a schottky contact? except that the metal junction is now replaced with another n type semiconductor junction?
 

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