What is Diode?

Fundamentally, A diode is a two terminal electronic device which allows current to flow in one direction only. Means, it conducts only in forward direction (forward biased) and it does not conduct in reverse direction (reverse biased). (discussed in details in the working of diode)

Ideally, Diode provides zero resistance path to current when it is forward biased and infinite resistance path when it is reverse biased. (we will study biasing further in this article).

Although, practically zero and infinite resistance is not feasible, so it provides negligible resistance in forward direction and very high resistance in reverse direction.

As a diode practically offer some resistance in forward direction (biasing condition) although it is negligible, a small energy is dissipated in forward biased diode that's why a diode is characterized as a passive element.

Due to the nature of conduction of current i.e. one directional only, diode is characterized as unilateral or unidirectional device and it acts as a one-way switch in circuits.

Diode Construction

A diode is a two terminal semiconductor device which is formed by the combining the p-type semiconductor and n-type semiconductor.

As a diode is formed by combination of p-type semiconductor and n-type semiconductor, it is also called a p-n junction diode.

A p-type semiconductor is formed by adding a trivalent impurity like Gallium, Indium, Boron etc. to instrinsic semiconductor like silicon and germanium. In p-type semiconductor majority charge carriers are holes and minority charge carriers are electrons, that means it as some vacant position to accept some electrons. That’s why it is also called acceptor.

A n-type semiconductor is formed by adding a pentavalent impurity like Arsenic, Antimony, Bismuth etc. to instrinsic semiconductor like silicon and germanium. In n-type semiconductor majority charge carriers are electrons and minority charge carriers are holes, that means it as some free electrons to donate. That’s why it is also called donor.

Note :- The concentration of free electrons and holes in n-type and p-type semiconductor can be alter by altering the doping concentration. Doping means adding impurity to intrinsic semiconductor.

If we combine p-type semiconductor to n-type semiconductor a p-n junction diode is formed. While combining these two materials following processes are initiated.

Holes from p-type semiconductor diffuse into n-region and recombine with free electrons present in n-region.

Electrons from n-type semiconductor diffuse into p-region and recombine with holes present in p-region.

After the certain amount of recombination of electrons and holes at the junction. A layer of electrons is created in p region and a layer of holes (positive ions) in n region is created due to restraining force. Due to these layers of electron and holes a potential barrier is created.

The region where recombination of electrons and holes take place is called depletion region. There are no charge carriers present in this depletion region.

This potential barrier has different value for different semiconductor like for germanium diode it is of 0.2 volt and for silicon diode it is of 0.7 volt. And for power diode it varies between 1.5 to 3 volt.

Diode Symbol

The symbolical representation of diode is shown in given figure which we can use in circuit diagram.

In this figure we saw a triangle, which flat side denoted to p-type semiconductor and pointed side denoted to n-type semiconductor.

As P-type semiconductor side have majority charge carriers are holes that is referred as positive charge, so this side is referred as anode and has positive polarity.

Similarly, N-type semiconductor side have majority charge carriers are electrons that is referred as negative charge, so this side is referred as cathode and has negative polarity.

Basically, this symbol represents the direction of conventional current flow as it is only flow in one direction only that is from anode (P side) to cathode (N side) in forward biasing. The process of conventional current flowing is discussed in working of diode.

Questions Covered in this Article

What is called diode?

See first paragraph

How diode is formed?

See diode construction

Diode is unidirectional or bidirectional?

Diode is unidirectional or unilateral device

Why diode is unidirectional device?

Due to one directional nature of conduction of current.

What is anode and cathode in diode?

Anode is positive terminal of diode which refers to p side of p-n junction diode and cathode is negative terminal which refers to n side of p-n junction diode.

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