P-N Junction Diode

A p-n junction diode is used for passing the current in one direction. It is a two-terminal or two electrode semiconductor device. This diode helps in stopping the current in the reverse or opposite direction. The electric current flows if the diode is forward biassed. But if the diode is reversed biassed it blocks the electric current flow. a p-n junction semiconductor diode is sometimes referred to as a p-n junction diode or semiconductor device. 

What is a P-N junction diode?

P-N junction diode is used for passing the current in one direction. The electrons which are free from bond carry charge carriers in n-type semicon type semiconductor sectors. Whereas holes are the majority charge carriers in p-. A p-n junction is formed when an n-type semiconductor is interlinked to a p-type semiconductor. But, p–n junction diodes are created due to the interlinking of p-type and n-type semiconductors. 

A semiconductor is made using materials such as silicon, germanium, and gallium arsenide. These materials are also used to make p-n junction diodes. Silicon is used over germanium when creating these junction diodes. Silicon works best for semiconductors because they work well in high temperatures. But p-n junctions diodes are composed of germanium. 

In a forward-biassed diode, the positive side is on the left and the negative side is on the right. Whereas in reverse biassed it is vice versa. The Arrowhead of these diodes indicates the direction of flow of electric current that is from a positive terminal to the negative side in the forward-biassed diode. These holes move from the anode i.e the positive terminal to the cathode which is the negative terminal. This flow is described as the conventional flow of current. 

On the other hand, free electrons move from the cathode (negative terminal ) to the anode (positive terminal). These electrons carry the charge. But due to the age-old notion, we always assume current flows from the positive to the negative terminal. 

Biassing of p-n junction semiconductor diodes

Providing an external voltage to a p-n junction semiconductor diode is called biassing. The external voltage that is applied to the p-n junction diode is done in two different ways i.e forward or reverse biassing technique. The electric current that flows through the p-n junction diode is called a forward-biassed current.

In a p-type semiconductor, the positive terminal of the battery is under forwarding bias. Whereas the n-type semiconductor diode is connected to the negative side of the battery. If this diode is reversed the electric current doesn’t flow. In the reverse system, the negative side is connected to the p-type and the n-type has the positive side of the terminal. 

Terminals of p-n junction diode

In simple terms, a terminal is a point or place where the flow of current begins or stops. For example, a bus terminal or terminus is a place where all buses start their journey or stop for the day. In a p-n junction diode, the term terminal is a point where charge carriers begin their flow or stop.

The two terminals of a p–n junction diode are either positive or negative. All free electrons will end their charges and all holes will begin at the positive terminal. Whereas all free electrons will start and all holes will end at the negative terminal. 

What happens in a forward-biassed semiconductor diode? 

The anode is a positive terminal in a forward-biased p-n junction diode (that p-type is linked to the positive terminal and n-type is connected to the negative). On this type of junction, the cathode terminal is negative.

The anode is a positively charged electrode or wire that charges the p-n junction with holes. In this, the source of positive charge carriers (i.e holes) is the anode or anode terminal or you can say positive terminal. The positive charge carriers (holes) begin their flow at the anode terminal, pass through the diode, and finally end up at the cathode or negative terminal. 

What happens in a reverse-biassed semiconductor diode? 

The anode becomes a negative side when the diode is reverse biassed (i.e p-type is linked to the negative terminal and n-type connected to the positive point). In this, the cathode terminal becomes a positive. In the reverse p-n junction there are free electrons from the anode which is called the negative terminal. In this diode, the anode terminal is the source of free electrons that will start their journey at the negative or anode terminal. They will later fill the many holes in the p-type semiconductor. In a p-type semiconductor, the holes are attracted to the negative terminal. 

This is because of the broad depletion region at the p–n junction that prevents or opposes the flow of free electrons from the negative terminal. The free electrons cannot travel from the positive terminal. The p-n junction receives holes from the cathode terminal, also referred to as the positive terminal.

The cathode terminal is the source of holes and the electrons start their journey at the positive or cathode terminal and eventually occupy the electron position in an n-type semiconductor. In an n-type semiconductor, free electrons are pushed towards the positive terminal because the depletion zone at the p–n junction blocks the flow of holes. 

What is the P-N junction diode’s importance? 

The p-n junction diode is by far the most basic semiconductor device, and its design is used to generate several additional semiconductor devices. This p-n junction diode is one of the most commonly used electronic components after resistors and capacitors.

This junction diode is the most common type of semiconductor diode. It is often used for a variety of rectification applications, including large and small currents, as well as high and low voltage levels, and it’s found in a wide range of electronic circuit designs nowadays. 

The fact that the p-n junction allows current to flow in one direction is very useful in creating many other devices. As current is a flow of electrons, it is only allowed to travel in one direction across any device and is not allowed to flow in the opposite direction with the help of a junction.

Conclusion 

p-n junctions are composed of n-type and p-type semiconductors materials. N-type has more concentration of electrons while p-type has more concentration of holes. p-n junctions are useful in the composition of many high-end devices where the flow of current has to be restricted or has to be allowed from one direction only. In the article above we have explained your p-n junction examples as well p-n junction importance.