Characteristics and Working of P-N Junction
Diode
Before going to the discussion of diode, we have to check the details of P-N junction. P-N junction can be defined as the
junction formed at combining point of P-Type & N-type material. The interface between the two regions is called as
metallurgical junction. At this junction we can also observe that depletion region will be formed.
Formation of Depletion Region:
In a step graded P-N junction, there exists a concentration gradient near the junction. There is large number of holes on N
side, near the junction. Those holes start moving from P side to N side i.e. from high concentration area to low concentration
area. This is nothing but diffusion of holes from P side to N side. Similarly the electrons on N side start diffusing across the
junction into the P region.
As holes enter the N region, they find number of donor atoms. The holes recombine with donor atoms. As donor atoms
accept additional holes, they become positively charged immobile ions. Atoms on P side are acceptor atoms. The electrons
diffusing from N side to P side recombine with the acceptor atoms on P side. As acceptor atoms accept additional electrons,
they become negatively charged immobile ions. Such a large number of negatively charged ions get formed near the
junction on P side.
As more number of holes diffuses on N side, large positive charge will be accumulated on N side near the junction.
Eventually in the same way large negative charge will be accumulated on P side near the junction. Such a region is depleted
of free mobile charge carriers and hence it is called “depletion region” or “depletion layer”.
The depletion region is also called “space charge region” if the depletion region can become widened up to a point where no
further electrons are holes can cross the junction. Thus depletion region can acts as the barrier.
Diode
Before going to the discussion of diode, we have to check the details of P-N junction. P-N junction can be defined as the
junction formed at combining point of P-Type & N-type material. The interface between the two regions is called as
metallurgical junction. At this junction we can also observe that depletion region will be formed.
Formation of Depletion Region:
In a step graded P-N junction, there exists a concentration gradient near the junction. There is large number of holes on N
side, near the junction. Those holes start moving from P side to N side i.e. from high concentration area to low concentration
area. This is nothing but diffusion of holes from P side to N side. Similarly the electrons on N side start diffusing across the
junction into the P region.
As holes enter the N region, they find number of donor atoms. The holes recombine with donor atoms. As donor atoms
accept additional holes, they become positively charged immobile ions. Atoms on P side are acceptor atoms. The electrons
diffusing from N side to P side recombine with the acceptor atoms on P side. As acceptor atoms accept additional electrons,
they become negatively charged immobile ions. Such a large number of negatively charged ions get formed near the
junction on P side.
As more number of holes diffuses on N side, large positive charge will be accumulated on N side near the junction.
Eventually in the same way large negative charge will be accumulated on P side near the junction. Such a region is depleted
of free mobile charge carriers and hence it is called “depletion region” or “depletion layer”.
The depletion region is also called “space charge region” if the depletion region can become widened up to a point where no
further electrons are holes can cross the junction. Thus depletion region can acts as the barrier.
