What is Diode ?

A Diode is a semiconductor device that essentially acts as a one-way switch for current. It allows current to flow easily in one direction, but severely restricts current from flowing in the opposite direction.

What is PN junction diode ?

A PN junction diode, as the name itself suggests, is an interface that acts as a boundary between two types, P and N, especially inside a semiconductor. This diode is created by a method called doping. This process is possible because the P diode has an excess number of holes, and the N diode has an excess number of electrons. Moreover, the region formed between the two diodes is also known as the depletion region, where both positive and negative charges are located on either side of the junctions.
In this article, let us delve deeper into the PN Junction Diode and understand forward bias and backward bias, besides learning about PN Junction Diode Characteristics specifically.
PN Junction Diode
A semiconductor is a material with its conductivity lying between conductors and insulators. Semiconductors fall under the category of intrinsic and extrinsic semiconductors, where the latter are sub-segmented as N-type and P-type semiconductors. Where a junction is created between these two semiconductors, it is referred to as P-N Junction. A diode in this regard is a device that regulates the electric flow inside a circuit.
Formation of P-N Junction:

The P-N junction is created through the doping method where the p-side has an excess of holes, and the n-side features an excess of electrons.
When we employ multiple semiconductor materials to create a P-N junction, a grain boundary is created that restricts electrons’ movement in two ways. This happens due to the scattering of electrons and holes, which is called doping. What follows the formation of the PN junction are – diffusion and drift. These confirm the difference in the concentration of holes and electrons on both sides of the junction. The holes from the p-side diffuse towards the n-side, whereas electrons on the n-side diffuse to the p-side. This results in the diffusion current across the junction.
Firstly, to understand how a PN junction diode works, we need to learn more about the two operating systems, and the general bias conditions.

PN Junction Diode Working:

Firstly, to understand how a PN junction diode works, we need to learn more about the two operating systems, and the general bias conditions.

Zero Bias

There is no external voltage applied in this semiconductor, which means there is no change in the state of electrons or diodes. 

Forward Bias:


In simple, The P-N junction is categorized under forward bias when the p-type is connected to the positive terminal of the battery and the n-type is hooked to the negative one. There is the built-in electric field at the p-n junction and the applied electric field, which will be in opposite directions in case of forward bias.
Typically, in the forward bias of a semiconductor circuit, the p-type diode is connected directly to the positive terminal, and the n-type diode is connected to the negative terminal. This type of semi-conductor circuit is known as forwarding bias. Moreover, once the electricity is turned on, the different electric fields are acting in opposite directions. However, in the case of forward bias, the resultant magnitude of the electric field is lesser, which means the depleted field observed in the circuit will be thinner.
So as the applied voltage is increased, the depleted region in the semi-conductor will attain a negligible state. At a point when the resistance of the depletion area becomes negligible, it facilitates the free flow of current.
In forward bias, the key components that you learn about are battery-induced electric field, built-in electric field, conventional current, and electron current
Reverse Bias:

In the reverse bias of the P-N Junction, the p-type is connected to the battery’s negative terminal, and the n-type is connected to its positive side. Here, the built-in electric field and the applied electric field are spotted in the same direction. As the two fields integrate, it results in the formation of an electric field that lies in the same direction as the built-in electric field. This creates a more resistive and far thicker region of depletion. This region becomes more resistive and thicker when the applied voltage gets larger.
So, as you can guess from the above sections, in the reverse bias of the PN Junction, the p-type diode is directly connected to the negative terminal, whereas the n-type diode is linked to the positive terminal. Unlike the forwards bias system, in the case of reverse bias, both the built-in electric field, as well as the electric current is in the same direction, which in turn creates more resistance inside the semi-conductor. That will result in the increase of the depleted region in P-N Junction. And along with the increase, the size of the depleted region will also increase.
In case of reverse bias, please make note of the following aspects for improved learning – battery-induced electric field and built-in electric field.

Application of PN Junction Diode

Technical applications

  • In general, the PN junction diode is used as a rectifier to convert AC current into DC current
  • Zener diode is a special kind of P-N junction diode is used in circuits to manage the regulation of voltage
  • In electrical circuit, the diode is deployed as a switch that turns on and off small circuits inside a more complex circuit
  • As a reverse-biased P-N junction diode, it is used as a photodiode since it is light-sensitive.
  • LED also constitutes a distinct kind of P-N junction diode, in the case of a forward basis that emits light.

P-N junction Diode in regular uses

  • It can be used as solar cells
  • LED applications
  • Equipment like oscillators and electric circuits


Diode symbol and PN Junction diode