# Diodes – geeksforjobs

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## Pn junction diode

A device that has a p-region on one side and an n-region on the other side is called a PN junction diode.

If the junction is used for the construction of the junction then the pn junction is classified based on the construction of the junction and the material.

They are:

1. Unemployed pn junction

2.Diffussion Junction

## Alloy junction

The aluminum PN junction is made by placing aluminum pellets or small balls on an L-type semiconductor. It is then heated to 600 c. Melt aluminum pellets and penetrate through an N-type semiconductor. Thus the composition will result in an alloy of Al & Semiconductor and then slow cooling. Since Al is a P-type impurity, the upper layer becomes P-type and then becomes a PN junction.

The concentration of holes and electrons in the alloy pn junction will be the same throughout the diode. It is also called as Abnpt PN junction or step-graded PN junction. Due to the concentration gradient, the holes propagate from the p-side to the n-side, and electrons propagate from the n-type to the p-type. When the carriers propagate from the N-side P-side and P-side to the N-side, holes and free electrons will appear on either side of the junction. The area is called the subtracted area. In this region, the recombination rate in electrons and holes will increase. This will cause a field of holes and electrons to appear on either side of the junction. This region is also called the space charge field or transition zone.

This region is empty of holes and electrons, but there are charge carriers in this region. These emerging charge carriers will be in the form of negative accessor ion or positive donor ion. The electric field is decreased due to the presence of negative acceptor ions and the presence of positive donor ions. This power filed will be directed from the N-region to the P-region. This electric field will resist the forward motion of the pores from the P-side to the N-side and electrons from the N-side to the P-side. The charge density inside the depletion region is not equal to zero due to the presence of immobile charge carriers inside the depletion region. And outside the depletion region, the charge density will be zero due to recombination of electrons and vice versa.

The electric potential due to charges present in the depletion region also presents in the depletion region. This potential is called the intrinsic potential or diffusion potential or contact potential or inhibitory potential.

## Distracted PN Junction

The diffused pn junction is fabricated in integrated circuits. Pn To fabricate the junction, a lightly p-type silicon wafer is used as the substrate. The N-type epithelial layer is grown on a P-type substrate using chemical vapor deposition. The SIO2 layer is formed on the N-type epitaxial region. Oxidation. A part of the silicon layer is removed by photolithography or etching process. Trent impurity boron is then diffused into n-type through impurity diffusion. This results in a p-region. Such a pn junction is called diffused pn junction. In this type of PN junction, the concentration of holes and electrons is not the same throughout the junction. There will be a difference in the concentration of holes and electrons throughout the junction.