Pn Junction Diode: Electrons, Holes, and Immobile Ions

In summary: The concentration gradient refers to the difference in concentration of a substance between two points. In the context of the conversation, it refers to the difference in concentration of electrons and holes between the n-side and p-side of the pn-junction. This difference in concentration is what causes diffusion to occur.
  • #1
logearav
338
0
folks, when a pn junction diode is formed, electrons in the n type and holes in the p type diffuse. agreed. then how immobile ions are formed at the vicinity of the junction leading to depletion region? how these immobile ions prevent further diffusion?
it is being said electrons and holes recombine after crossing the junction? actually what is recombination mean? what is space charge? please help.
 
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  • #3
The regions nearby the PN interfaces lose their neutrality and become charged, forming the space charge region or depletion layer .The electric field created by the space charge region opposes the diffusion process for both electrons and holes
mr. naty1, i don't understand these two lines mentioned in wikipedia article suggested by you. space charge contains negative ions on p side and positive ions on n side. if this being the case naturally attraction between holes and negative ions should occur on the p side and same being the case between electrons and positive ions on the n side. then how electric field opposes further diffusion.?
The space charge region has the same charge on both sides of the PN interfaces, thus it extends farther on the less doped side

i don't understand this line too because space charge has negative charge and positive charge but how the statement says 'same charge on both sides " please help sir
 
  • #4
The regions nearby the PN interfaces lose their neutrality and become charged, forming the space charge region or depletion layer .The electric field created by the space charge region opposes the diffusion process for both electrons and holes
mr. naty1, i don't understand these two lines mentioned in wikipedia article suggested by you. space charge contains negative ions on p side and positive ions on n side. if this being the case naturally attraction between holes and negative ions should occur on the p side and same being the case between electrons and positive ions on the n side. then how electric field opposes further diffusion.?
The space charge region has the same charge on both sides of the PN interfaces, thus it extends farther on the less doped side i don't understand this line too because space charge has negative charge and positive charge but how the statement says 'same charge on both sides " please help sir
 
  • #5
Heres a couple of thoughts that may or may not help out in some manner.

On one side is a bunch of extra electrons not bound very tightly. On the otherside is a bunch of extra holes (spots in the 3d structure that are very likely to attract and hold an electron). Both sides are neutral since the number/charge of the electrons and protons balance as long as they are kept apart...

This situation changes when the 2 materials are placed together. Some of the close by electrons jump into the big holes (perhaps leaving a smaller hole behind). Pretty soon you have a region of space in the middle where it looks like there are no holes or electrons (actually the electrons are there, but since they are stuck in a hole, they do not easily move around or do much of anything - give them a good hit with another electron and you will see an electron/hole pair pop back out at you).

It is difficult for electrons to diffuse through this region as there are no big holes to jump into and electrons are held too tightly to be bumped along from hole to hole inside the material.
 
  • #6
logearav said:
The regions nearby the PN interfaces lose their neutrality and become charged, forming the space charge region or depletion layer .The electric field created by the space charge region opposes the diffusion process for both electrons and holes
mr. naty1, i don't understand these two lines mentioned in wikipedia article suggested by you. space charge contains negative ions on p side and positive ions on n side. if this being the case naturally attraction between holes and negative ions should occur on the p side and same being the case between electrons and positive ions on the n side. then how electric field opposes further diffusion.?
The process begins by electrons on the n-side and holes on the p-side crossing the pn-junction because there exists a concentration gradient causing diffusion. The space-charged region formed opposes this diffusion because the negative ions on the p-side opposes the diffusion of electrons from the n-side. Similarly for the positive ions on the p-side. This occurs until equilibrium has been reached.

The space charge region has the same charge on both sides of the PN interfaces, thus it extends farther on the less doped side i don't understand this line too because space charge has negative charge and positive charge but how the statement says 'same charge on both sides " please help sir
What this means is that magnitude of the net negative charge on the p-side is the same as the magnitude of the net positive charge on the n-side, which makes complete sense because for every positive/negative ion which is exposed after an electron/hole pair recombines, overall charge neutrality of the device is preserved.
 
  • #7
many thanks mr.edguy99 and mr. defennder for your replies.
what is concentration gradient sir?
 

What is a Pn Junction Diode?

A Pn Junction Diode is a type of semiconductor device that consists of two regions - a P-type semiconductor and an N-type semiconductor - that are joined together. This junction between the two regions creates a depletion region where there are no free charge carriers.

What are Electrons, Holes, and Immobile Ions in a Pn Junction Diode?

Electrons are negatively charged particles that are found in the N-type region of a Pn Junction Diode. Holes are positively charged particles that are found in the P-type region. Immobile ions are charged particles that are present in the depletion region and do not move.

How do Electrons, Holes, and Immobile Ions contribute to the functionality of a Pn Junction Diode?

Electrons and holes are responsible for the flow of electric current in a Pn Junction Diode. When a voltage is applied to the diode, the electrons and holes move towards the depletion region, creating a flow of current. Immobile ions help to maintain the electric field in the depletion region.

What is the role of the depletion region in a Pn Junction Diode?

The depletion region in a Pn Junction Diode creates a barrier between the two regions of different doping. This barrier prevents the flow of electric current in the absence of an external voltage. When a voltage is applied, the depletion region becomes narrower, allowing current to flow through the diode.

What are the applications of Pn Junction Diodes?

Pn Junction Diodes have a wide range of applications, including rectification, signal modulation, and voltage regulation. They are also used in solar cells, LEDs, and photodiodes. Pn Junction Diodes are essential components in electronic circuits and can be found in a variety of devices such as computers, televisions, and mobile phones.

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