explain P-N Junction Diode

Now, any free charge which wanders into the depletion zone finds itself in a region with no other free charges. Locally it sees a lot of positive charges (the donor atoms) on the n-type side and a lot of negative charges (the acceptor atoms) on the p-type side. These exert a force on the free charge, driving it back to its 'own side' of the junction away from the depletion zone. A free charge now requires some extra energy to overcome the forces from the donor/acceptor atoms to be able to cross the zone. The junction therefore acts like a barrier, blocking any charge flow (current) across the barrier.

     We create a p-n junction by joining together two pieces of semiconductor, one doped n-type, the other p-type. This causes a depletion zone to form around the junction between the two materials. This zone controls the behavior of the diode.

When we apply a potential difference between the two wires in one direction we tend to pull the free electrons and holes away from the junction. This makes it even harder for
them to cross the depletion zone.
When we apply the voltage the other way around we push electrons and holes towards the junction, helping to give them extra energy and giving them a chance to cross the junction.

Therefore, when a p-n junction is reverse biased, there will be no current flow because of majority carriers but a very small amount of current because of minority carriers crossing the junction.
               However, at normal operating temperatures, this small current may be neglected.


In summary, the most important point to remember about the p-n junction diode is its ability to offer very little resistance to current flow in the forward-bias direction but maximum resistance to current flow when reverse biased.