I – V characteristics

The relationship between the current flowing through the diode and the voltage due to the applied voltage in forward bias and reverse bias is shown by a graph.  Thus showing the voltage and diode current through the graph is called VI characteristics of the diode. 

The PN junction diode is made by combining p and an n-type semiconductor with a blocking force between the two semiconductors. The forward current value depends on the amount of forward voltage having a direct relationship between the two. This relation is called I-V Characteristics of PN Junction.

Biasing 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 biasing conditions for p-n junction diodes:

• Forward bias: The p-n junction is said to be 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-biased 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.

V-I characteristics of p-n junction diode

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:

1. 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.

2. 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, which is nearly linear.

3. 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.

Zener breakdown

When the reverse bias voltage is applied across the pn terminals, the depletion region begins to increase. As a result, more electrons and holes are generated.

These electrons and holes produce a very powerful electric field across the junction of the diode. The magnitude of the electric field will depend on the magnitude of the applied reverse voltage.

The electric field exerts an electron force which is present in the valence band. This will enter the conduction band, and the conduction process begins.

This phenomenon is called Zener breakdown.

Avalanche breakdown

The free electrons move across the depletion region of the diode. They possess velocity, and the electrons acquire kinetic energy. Due to the presence of velocity, the minority carriers randomly move inside the diode. It collides with stationary electrons held to the atom by covalent bonding.

The covalent bonding gets broken by bound electrons, and the conduction process begins. The electrons transfer the kinetic energy to stationary electrons which makes them move. As the magnitude of the reverse bias voltage increases, the energy rises. The resulting collision produces a current, which causes the breakdown of the diode.

This breakdown is called an avalanche breakdown.

Forward current in PN junction

When the battery voltage is applied there on the forward bias junction, a constant current will flow via this junction.

Reverse current in pn junction

When a pn junction is conjointly in a battery in that its n-type region is conjoint to the positive power of the battery and the p-type region is connected to the negative power of the battery then the pn junction is said to be in reverse biased condition. Ideally, no current flows through the junction.

Conclusion 

The diode’s capacity to work as two separate but equally effective devices makes it a very versatile component. The various sorts of diode biasing effects provide you complete choice over which function the diode will perform in your circuit design. The use of forward and reverse bias gives the circuit designer complete control of the diode operation.

Study material notes on 1- V characteristics in forward and reverse bias, we can get at a fact – a PN junction diode conducts current only in one direction – i.e. during forward bias.  During forward bias, the diode conducts current with an increase in voltage. During reverse bias, the diode does not conduct with an increase in voltage.