P- N Junction-Definition

Let us look at the definition of p-n junction. A P- N junction diode is a semiconductor device that controls the current in a circuit. It consists of two types of semiconducting materials: the p-type and the n-type material is Silicon or Germanium consisting of atomic impurities. 

We can say a junction is forward biassed when the voltage applied causes ease in the current and a junction is said to be reverse-biassed when the voltage is applied to the diode in the opposite direction.

V-I characteristics of p-n junction diode

Now that we know the definition of p-n junction, let us look into the characteristics of the same. A curve between the voltage and current through the circuit defines the V-I properties of P-N junction diodes. The x-axis represents voltage, while the y-axis represents current. Suppose the V-I characteristics of the p-n junction diode are plotted on a graph; we can see that the diode works in three different zones, which are:

Zero bias

No external voltage is delivered to the p-n junction in a zero bias condition,

As a result, the potential barrier at the junction prevents current flow.

As a result, when V = 0, the circuit current is zero.

Forward Bias

The p-type of the p-n junction forward bias is connected to the positive terminal of the external voltage, while the n-type is connected to the negative terminal.

As a result, the potential barrier is minimised.

The forward V-I characteristic of the P-N junction diode shows that the current grows exceptionally slowly at the beginning. The curve is nonlinear because the external voltage delivered to the p-n junction is used to overcome the potential barrier in this region.

The potential barrier is removed once the external voltage surpasses the possible barrier voltage and the p-n junction functions like an ordinary conductor. As a result, the curve AB climbs significantly as the external voltage rises, nearly linearly.

Reverse bias

The p-type of the p-n junction is connected to the negative terminal of the external voltage, while the n-type is connected to the positive terminal.

As a result, the potential barrier at the intersection is enhanced.

The junction resistance rises to an extremely high level and virtually no current flows through the circuit.

In practice, however, a very modest current of the order of micro-amperes travels across the circuit because of the minority carriers in the junction, this is known as reverse saturation current.

Formation of p-n junction

The doping process is used to create the p-n junction in a semiconductor. The doping method is used because if the semiconductor is formed by combining different semiconductor materials, it will include a grain boundary that will scatter holes and electrons and stop electron movement from one side to the other.

The doping process can be described as follows:

Consider the case of a thin p-type silicon semiconductor. With a small amount of pentavalent impurity to the semiconductor wafer, a region now becomes n-type silicon. The wafer has both p- and n-type regions separated by an interface or junction. After that, diffusion and drift processes take place.

The electrons from the n side diffuse to the p side due to a difference in electron concentration on one side of the junction and a concentration of holes on the other. The perforations on the p side diffuse to the n side in the same way. As a result, there is a diffusion current across the connection.

Current flow in a p-n junction diode

Let us discuss the working of p-n junction diodes. 

When the voltage is increased, electrons move from the n side to the p side of the junction. The movement of holes from the p side to the n side of the meeting occurs similarly as the voltage rises. As a result, a concentration gradient exists between the terminals on both sides. Further, due to the concentration gradient formation, charge carriers will shift from higher concentration regions to lower concentration parts. The current flow in the circuit is caused by the movement of charge carriers inside the p-n junction.

Biassing conditions for the p-n junction diode

In a p-n junction diode, there are two active regions:

P-type

N-type

The voltage applied determines one of three biassing conditions for p-n junction diodes:

• Forward bias: The p-n junction is forward-biassed, when the p-type is connected to the battery’s positive terminal and the n-type to the negative terminal.

• Reverse bias: The p-n junction is reverse-biassed, when the p-type is linked to the battery’s negative terminal and the n-type is attached to the positive side.

• Zero bias: The p-n junction diode is not exposed to any external voltage.

Conclusion

Semiconductors consist of two types of charge carriers, namely Holes and Electrons. These holes have a positive charge, whereas the Electron has a negative charge. The semiconductors are doped or added with impurities to increase their mobile charges. The depletion region is the region of junction that has no charge. When the Junction diode is biassed in the forwarding direction, the thickness of the depletion region decreases to ease the current flow through the circuit. When the junction diode is biassed in the reverse direction, the thickness increases of the depletion region and blocks the current flow.