Why potential of n side is higher in unbiased p-n junction

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Discussion Overview

The discussion revolves around the potential difference between the n-side and p-side of an unbiased p-n junction. Participants explore the reasons for the n-side being considered at a higher potential compared to the p-side, addressing concepts related to charge carriers, voltage, and the depletion region.

Discussion Character

  • Conceptual clarification
  • Debate/contested
  • Technical explanation

Main Points Raised

  • Some participants question the assertion that the n-side is at a higher potential without a battery connected, suggesting that without a current, both sides should be at the same potential.
  • Others propose that the n-side's higher potential is due to the presence of a battery connected to it, which would establish a voltage difference in a reverse-bias scenario.
  • One participant explains that the natural potential across a p-n junction arises from the diffusion of charge carriers, leading to a charge buildup that creates a potential barrier.
  • There is a discussion about whether a higher potential simply indicates that one side is more positively charged than the other, with some agreement on this interpretation.

Areas of Agreement / Disagreement

Participants do not reach a consensus on whether the n-side is indeed at a higher potential without a battery. Multiple competing views remain regarding the implications of charge distribution and the role of external voltage sources.

Contextual Notes

The discussion includes assumptions about the conditions under which the potential difference is considered, such as the presence or absence of a battery and the definitions of potential and charge. There are also references to specific voltage values and conditions that may not be universally applicable.

Rishav sapahi
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why the potential of n side is higher than that of the p side when no battery is connected to the p-n junction?
 
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Well if there is no battery, the circuit is pretty much useless... The p-n junction is typically associated with a voltage drop across the p-n junction (somewhere around .5-3V for LEDs). However with no battery in the circuit, there will be no current flowing and thus no voltage across the junction, so they should be at the same potential.
 
but in my book they are stating that n-side is at higher potential without any explanation
 
Is the battery attached to the n-side? If so, then yes, the n-side would be at a higher potential and the p-side would be a 0V, since there in no (practically none) current flowing through the diode. This is known as the reverse-bias direction. The voltage at the n-side would be at the same voltage as the battery (assuming it is just connected with a wire).
 
Look up "PN junction depletion region". The natural potential that develops spontaneously across a PN junction is due to the diffusion of charge carriers across the junction. P type material has "holes" in its bond structure that can be "filled" by accepting electrons, while the N side has more than enough conduction electrons to satisfy its bond requirements.

However, every electron that crosses over leaves a small net positive charge in the N material, while the P side gains a small negative charge. These charges build up until they suppress further movement --- they raise a potential barrier against further diffusion of charges. This is what leads to the "turn on" bias requirement to get current moving across the junction (about 0.7V for silicon PN junctions).
 
so Is high potential just means that given side is more positively charged than other
 
Rishav sapahi said:
so Is high potential just means that given side is more positively charged than other

Yes. A potential develops across the junction.
 

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