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

In summary: This potential is due to the diffusion of charge carriers across the junction. The potential is highest on the side with more positive charges.
  • #1
Rishav sapahi
19
0
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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  • #2
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.
 
  • #3
but in my book they are stating that n-side is at higher potential without any explanation
 
  • #4
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).
 
  • #5
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).
 
  • #6
so Is high potential just means that given side is more positively charged than other
 
  • #7
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.
 

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

1. Why is the potential of the n side higher in an unbiased p-n junction?

The potential of the n side is higher in an unbiased p-n junction because of the difference in electron concentration between the n and p regions. The n region has a higher concentration of free electrons compared to the p region, resulting in a higher negative charge on the n side and a higher positive charge on the p side. This creates an electric field that causes the potential to be higher on the n side.

2. How does the potential difference affect the behavior of the p-n junction?

The potential difference in a p-n junction controls the flow of electrons and holes across the junction. When the junction is unbiased, there is a depletion region at the interface which prevents the majority carriers (electrons in n region and holes in p region) from crossing the junction. However, when a potential difference is applied, electrons and holes can move across the junction, resulting in a flow of current.

3. Can the potential of the n side ever be lower than the p side in an unbiased p-n junction?

No, the potential of the n side cannot be lower than the p side in an unbiased p-n junction. This is because the majority carriers in the n region (electrons) have a higher mobility compared to the majority carriers in the p region (holes). Therefore, when the junction is unbiased, the n region will always have a higher potential due to the higher concentration and mobility of electrons.

4. How does the potential of the n side change when a forward bias is applied to the p-n junction?

When a forward bias is applied to the p-n junction, the potential of the n side decreases compared to the p side. This is because the applied voltage reduces the potential barrier at the junction, allowing more majority carriers to cross the junction. As a result, the positive charge on the n side decreases, and the negative charge on the p side increases, causing a decrease in potential on the n side.

5. What happens to the potential of the n side when a reverse bias is applied to the p-n junction?

When a reverse bias is applied to the p-n junction, the potential of the n side increases compared to the p side. This is because the applied voltage increases the potential barrier at the junction, preventing majority carriers from crossing the junction. As a result, the positive charge on the n side increases, and the negative charge on the p side decreases, causing an increase in potential on the n side.

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