doubt related to PN junction

[sp3]

Hi all,

I have a doubt related to diffusion current in PN junction :

After some electrons and holes diffuse into P and N region respectively they recombine with the majority carriers in the regions and vanish ( gone / out of scene). Here I am slightly confused with word vansih (gone / out of scene). Does it mean that after recombination, the electron-hole pair will get destroyed ?? but this may not be possible according to law of conservation of charges..if not where they will be ??

Please clear my doubts

Thanks in advance,
SP3

 

[atripathi]

Try understanding it like, they are no more mobile, and do not participate in current flow.

 

[retroo]

so ur problem is the word vanish??? correct..? lets go through that ...

the connection is depicted in the diagram..

After some electrons and holes diffuse into P and N region respectively they recombine with the majority carriers true and then they form neutral that is there is no electrons or holes...
guess there are 5 e n 5 holes... 5 e combine with the +ve charge in p region thus forming neutral and 5 holes combine with -ve charged N region to form neutral.
now the no of holes and electrons =0 or they vanished!!!

 

[LvW]

............
now the no of holes and electrons =0 or they vanished!!!

To make it clear: The electrons (and holes) did not "vanish", rather they are not "free" anymore but fixed within thr respective atom. Both have represented a movable charge before - and this kind of charge has vanished.

 

[retroo]

To make it clear: The electrons (and holes) did not "vanish", rather they are not "free" anymore but fixed within thr respective atom. Both have represented a movable charge before - and this kind of charge has vanished.

vanish in the sense the presence of holes or electrons no more.... (as the charge in them are lost they they will not be present in the device).Hope i too sated the same before and our points are more or the other same!!

 

[LvW]

In this context, another question arises:
If some electrons/holes have disappeared (or better: are not available anymore as movable charges), the charge of both areas that are doped differently has changed - and as the result there is the "diffusion voltage" (app. 0.6...0.7V) across the pn junction (of course without any external voltage). Is it possible to use such a device as a voltage source?

 

[sp3]

Hi retroo,

Thank you for your reply.

If the charges form neutral after recombination, how to defend law of conservation of charges.. because we can not create or destroy charges.. "forming neutral" is slightly confusing for me..

Thanks,
sp3

 

[2010ee179]

Posted by sp3
how to defend law of conservation of charges

Well, as far as i know...Charge is still present, not destroyed, rather it's effect is being neutralized by the hole after recombination...Surely, now it has lost its mobility and gonna stay somewhere near Junction..

 

[dgnani]

Hi retroo,

Thank you for your reply.

If the charges form neutral after recombination, how to defend law of conservation of charges.. because we can not create or destroy charges.. "forming neutral" is slightly confusing for me..

Thanks,
sp3

the total charge was zero even before recombination...

---------- Post added at 18:45 ---------- Previous post was at 18:40 ----------

In this context, another question arises:
If some electrons/holes have disappeared (or better: are not available anymore as movable charges), the charge of both areas that are doped differently has changed - and as the result there is the "diffusion voltage" (app. 0.6...0.7V) across the pn junction (of course without any external voltage). Is it possible to use such a device as a voltage source?

the answer is yes but the total charge stored in the junction is small; you need a way to re-supply the junction charge, this is how a photovoltaic cell works: it creates new e-h pairs that are separated by the field in the depletion region supplying new charge to the battery... as long as you do not draw too much current

 

[Elimathew]

i wanted to know whether there are equal number of free electron and holes in a PN junction diode if not what would happen .and i would also want to know the answer of the question
LvW asked previously

 

[2010ee179]

i would also want to know the answer of the question
LvW asked previously

I remember, my teacher once told me..."Bear in mind...built in potential of pn junction can not be used as voltage source..."

 

[LvW]

I remember, my teacher once told me..."Bear in mind...built in potential of pn junction can not be used as voltage source..."

Yes, I think you had a good teacher.