A question on p-n junction depletion layer

In summary, the p-n junction reaches thermal equilibrium after the initial movement of charges. The separation of charges creates an electric field that prevents further recombination. The device as a whole remains neutral. The fixed positive ions on the n-type region create an electric potential that balances the diffusion of free electrons from the region of high concentration to low concentration. This results in a stable depletion zone at the junction.
  • #1
cjs94
16
0
Hi,

I'm studying the p-n junction and I'm a little confused about the depletion layer that forms. I understand how electrons and holes diffuse across the junction, recombine and leave charged ions but what I don't understand is why the ions remain fixed around the junction. Surely the positive ions in the n-type region will attract the free electrons remaining in that region further away from the junction, effectively causing the ions to diffuse evenly throughout the n-type region?

Chris
 
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  • #2
cjs94 said:
Hi,

I'm studying the p-n junction and I'm a little confused about the depletion layer that forms. I understand how electrons and holes diffuse across the junction, recombine and leave charged ions but what I don't understand is why the ions remain fixed around the junction. Surely the positive ions in the n-type region will attract the free electrons remaining in that region further away from the junction, effectively causing the ions to diffuse evenly throughout the n-type region?

Chris

The junction is at thermal equilibrium after the movement of charges when the junction is created. An electric field is created from the charge separation that stops further recombination but the device as a whole is neutral.
http://www.optique-ingenieur.org/en/courses/OPI_ang_M05_C02/co/Contenu_05.html
 
  • #3
cjs94 said:
Surely the positive ions in the n-type region will attract the free electrons remaining in that region further away from the junction, effectively causing the ions to diffuse evenly throughout the n-type region?
Think in terms of two potentials, one is the chemical potential the other electric. The chemical potential drives free electrons from the region of high concentration (n side) to low concentration (p side). This action increases until the electric potential created by the exposed, fixed positive ions on the n side is strong enough to balance the diffusion arising from the chemical potential gradient. At this point, the depletion zone is stable (in equilibrium).
 

1. What is a p-n junction depletion layer?

A p-n junction depletion layer is a region that forms at the interface between a p-type and n-type semiconductor material. It is created by the diffusion of majority carriers from one side to the other, leaving behind an area of fixed charge. This creates an electric field that prevents further diffusion and results in a barrier for current flow.

2. How does the width of the depletion layer affect the behavior of a p-n junction?

The width of the depletion layer affects the barrier for current flow in a p-n junction. A wider depletion layer creates a higher barrier, resulting in a lower current flow. Conversely, a narrower depletion layer has a lower barrier and allows for a higher current flow.

3. What factors can influence the width of the depletion layer?

The width of the depletion layer is primarily influenced by the doping concentrations of the p-type and n-type materials. A higher doping concentration will result in a narrower depletion layer, while a lower doping concentration will result in a wider depletion layer.

4. How does the depletion layer behave under forward and reverse bias?

Under forward bias, the depletion layer becomes narrower, allowing for current flow to occur. Under reverse bias, the depletion layer becomes wider, creating a higher barrier for current flow. This results in a very small leakage current in the reverse direction.

5. What are some common applications of p-n junction depletion layers?

P-n junction depletion layers are essential components in electronic devices such as diodes, transistors, and solar cells. They are also used in photodetectors, where the depletion layer responds to light to generate a current.

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