PN JUNCTION DIODE

                     A PN junction is the basic of many electronic circuits and is considered to be the basic semiconductor device. The PN junction consists of a P type semiconductor and an N type semiconductor and it is formed in many ways one way is to take an extrinsic semiconductor device and then start doping equal amount of P type and N type impurities one from each side and allow uniform doping across the semiconductor, as the impurities get settled inside and at the center there will be one side p and other side n type as in fig 1 a. One more way to form a pn junction is take one P type semiconductor and another N type semiconductor and the join them together and heat at the junction as in fig 1 b.

As we know that the P side semiconductor consists of majority of holes and acceptor ions and the N Type consists of the majority electrons and donor ions. Their view is shown in the figure 2

At the junction now the electrons from the N Side will move towards the holes in the P type semiconductor  as a result the holes and the electrons get recombined and the process continues until no further electron and hole pair recombination is possible at a current temperature. The recombination process is shown below in the figure 3

As the recombination process continues at the junction, there will be a situation reached when no further recombination is possible, at that moment the area around the junction of P and N  is completely free of the free charge carriers i.e., the region is depleted of the charge carriers hence the region is called as depletion region, which is shown below in fig 4

The depletion region consists of the electric field due to the acceptor ions on the N side and the Donor ions on the P side due. As the depletion region is free of charge carriers it just works as an insulator and on both sides of depletion region there are charge carriers i.e., conductors, hence the depletion region is also used as capacitance and is famously called as Depletion Capacitance. The voltage across the depeletion region is called cut in voltage. This is how PN Junction is formed.