Drift vs Diffusion current

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Discussion Overview

The discussion revolves around the behavior of minority carriers in a forward-biased PN junction, specifically addressing the nature of diffusion and drift currents. Participants explore the mechanisms behind these currents and seek clarification on why minority carriers primarily contribute to diffusion current despite the presence of an applied electric field. The conversation touches on concepts from solid-state physics and electrical engineering.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant notes that in a forward-biased PN junction, the potential barrier decreases, allowing majority carriers to diffuse and form a diffusion current, while the drift current of minority carriers is insignificant.
  • Another participant expresses confusion about why minority carriers form a diffusion current rather than a drift current after crossing the potential barrier, highlighting the counter-intuitive nature of this phenomenon in the presence of an electric field.
  • Several participants reference textbooks and external resources, indicating that while they acknowledge the diffusion current, they find a lack of detailed explanations or proofs in the literature.
  • There is a suggestion that the discussion may be more aligned with solid-state physics than electrical engineering, as some participants feel that electrical engineering texts do not adequately address the underlying physics.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the reasons behind the predominance of diffusion current over drift current for minority carriers. There are multiple viewpoints regarding the adequacy of existing literature and resources to explain the observed phenomena.

Contextual Notes

Participants express limitations in the available literature, noting that many texts do not provide sufficient reasoning or proofs for the behavior of currents in PN junctions. There is also a recognition that the discussion may require a deeper understanding of solid-state physics concepts.

Amerez
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In a forward-biased PN junction, the potential barrier decreases, allowing more majority carriers from one side to diffuse to the other side where they are minority carriers. After they cross the potential barrier, they form a diffusion current, the drift current of minority carriers is insignificant, then they recombine with majority carriers and form a drift current under the effect of the applied electric field.

Why do minority carriers form a diffusion current not a drift current after they cross the potential barrier? It is counter-intuitive that the main current is diffusion when there is an applied electric field.

This is according to all the microelectronics book I'm currently reading. There is one which says this can be proved but without providing anything. Can someone please provide a proof for this.
 
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This is a good read on Transistor Action.

tran10.gif
 
I have went through the link you provided, but this doesn't touch on the question.
Maybe this thread is more solid-state physics than electrical engineering !?
 
maybe you'd like to borrow a book :-p
 

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lol, it may be the only way.
I'm actually reading through Sedra 5th edition on this matter, it states the current is a diffusion current but without giving the reasons. It seems electrical engineering books leave many holes when describing the physics of the devices
 
Amerez said:
I have went through the link you provided, but this doesn't touch on the question.
Maybe this thread is more solid-state physics than electrical engineering !?
You went through all that? Did you go through their links

Semiconductor concepts and Semiconductors for electronics
 
dlgoff said:
You went through all that? Did you go through their links

Semiconductor concepts and Semiconductors for electronics

Yes, I've been scanning this site for the past couple of weeks.
Most of the sites I've read seem to describe the operation of the PN junction or the diode, but I'm unable to find the answer to this specificity.
 

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