In P type semiconductor concentration of holes is more than
electrons and in N type semiconductor electrons concentration is
more than holes. When P-N junction type of semiconductor is
combined, holes from P side move towards N side and electrons from
n side move towards P side. In between, they collide and neutralize
to from P-N junction.
Thus, near the junction positive charge is built near N side and
negative charge is produced near P side.
This set up a potential difference across junction and from electric
field, E directed from N to P side. This generated electric field is strong
enough to stop further diffusion of majority charge carriers (but, it
helps minority charge carriers to drift across the junction). Either
sides of the junction becomes less dense of charge carriers and
becomes depleted called deletion region. From this point of time,
charge carriers need to overcome this potential barrier developed at
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