What is Diode or PN junction Diode?


Definition of Diode- It is a semiconductor device. Diode is a passive electronic component because diode does not require an external power source to operate. The following image is the image of a p-n junction diode with its polarities mentioned in it. The anode is positive terminal and cathode is negative terminal. .
In the above image a white or silver color stripe on one side of diode shows the cathode terminal. The basic property of diode is that it is a unidirectional component. Which means it allows the flow of current only in one direction. Diode allows the flow of current only when it is forward biased.


Construction of p-n junction diode

Most of the diodes are made up materials like silicon or germanium. Junction diode is made after joining two different types of semiconductor materials. As the name is self-explanatory one is p-type, and another is n-type semiconductor material.


Junction diode has two terminals, an anode and a cathode. In the p-type material holes are in the majority. And in the n-type material electrons are in the majority.

A pure semiconductor material with p-type impurity or trivalent impurity is called p-type semiconductor material. P-type impurity material has 3 electrons in its valence orbit. Pure semiconductor material with n-type impurity is called n-type or pentavalent semiconductor material. N-type impurity material has 5 electrons in its valence orbit.

How do diode work?

Diode works only when it is forward biased. As shown in image below.


A diode is said to be connected in forward bias when positive terminal of the battery is connected to the positive terminal (anode) of diode and negative terminal of battery is connected to the negative terminal (cathode) of diode.

Diode does not work and does not allow the flow of current when it is reverse biased. As shown in image below.


A diode is reverse biased when positive terminal of the battery is connected to the negative terminal (cathode) of diode and negative terminal of battery is connected to the positive terminal (anode) of diode. For the diode to conduct current through it the potential difference applied in a forward biased diode should be at least 0.7V in the case of silicon p-n junction diodes to overcome the depletion region. In reverse biased condition diode works as an insulator. When reverse biased voltage is applied to the diode there is no current flow through the diode. But when that reverse voltage exceeds a voltage called breakdown voltage the current suddenly increases exponentially. It leads to a shorted diode. For a small change in applied voltage, leads to a high increase in net current through the diode.



Symbol of Diode




Uses Or Applications of diode

Diodes are used in rectifier circuits to convert alternating current into direct current, in half wave and full wave rectifier circuits. Diode is used in signal limiter. Diodes are used in switches. It is also used in signal modulators and signal demodulators. Used in oscillator circuits and signal mixers etc.