#Diode is an electronic device with two terminals and conducts current only in one direction. Diodes have low resistance in one direction (ideally zero) and high resistance in the reverse direction (ideally infinite) so the current flows only in one direction. There are various types of diodes such as PN Junction diode, Zener diode, Tunnel diode, Varactor diode, Schottky diode, Photodiode, PIN diode, Laser diode, Avalanche diode, Light Emitting Diode. Let us understand the PN junction diode in detail.
PN Junction diode
PN Junction diode is a #semiconductor device that allows the flow of #current in one direction. It is the basic semiconductor diode. A PN junction diode is formed by doping a p-type material on one side and an n-type material on another side of a silicon substrate. The voltage versus current (V-I) characteristics of the PN Junction diode appear to be exponential.
The symbol of the PN Junction diode under forward bias condition is given below
Biasing is the process of applying an external voltage to the PN Junction diode. PN Junction diode can be biased in three ways: zero bias, forward bias, and reverse bias.
Zero bias condition is the biasing condition when no external voltage is applied to the PN junction diode.
The PN Junction diode is said to be in forward bias when the positive terminal of the battery is connected to p-type and the negative terminal of the battery is connected to the n-type of the diode.
The PN Junction diode is said to be in reverse bias when the positive terminal of the battery is connected to n-type and the negative terminal of the battery is connected to the p-type of the diode.
PN Junction diode under Zero Bias
In zero bias condition, there is no external #voltage and as a result, electrons diffuse from n side to p-side and the holes diffuse from p side to n side through the junction and combine with each other. These carriers establish an electric field and that electric opposes the further #diffusion of carriers and a region of immobile charges is created at the junction known as the depletion region.
PN Junction diode under Forward Bias
In the forward bias condition, #electrons from the n side are repelled by the negative terminal of the battery and are moved towards the p side and the positive terminal of the battery attracts the electrons from the p region and the #holes from the p region move towards the n side and are attracted by the negative terminal of the battery and by the movement of the carriers current flows through the diode. In forward bias condition, the width of the depletion region decreases, and the potential barrier across the junction also decreases which in turn decreases the resistance and increases the flow of current.
V-I characteristics - Forward bias
In forward bias condition, by supplying the positive voltage the charges carriers, i.e., electrons and holes get enough energy to cross the junction, and a current called forward current flows through the diode. The voltage at which a large current flows through the diode is called cut-in voltage. The cut in voltages of Si, Ge, and GaAs are 0.7V, 0.3V, and 1.2V respectively.
PN Junction diode under Reverse Bias
In the reverse bias condition, the electrons are attracted by the positive voltage applied to the n-type, and holes are attracted by the negative voltage applied to the p-type. As a result, the electrons and holes move away from the junction and the width of the depletion regions increases, and the barrier potential also increased and a high impedance path is established and thus the current flow due to majority charge carriers is prevented. However, some minority charge carriers cross the junction, and a small amount of current known as reverse current flows through the diode.
V-I characteristics - Reverse Bias
In the Reverse Bias, as the current flow is due to minority charge carriers the current is very small and it is known as reverse saturation current. When the reverse voltage is applied beyond the limit, the reverse current increases drastically and the junction may break down. The voltage at which the breakdown of the junction occurs is called Reverse breakdown voltage. Zener breakdown and Avalanche breakdown are the two mechanisms by which diode breakdown occurs.
V-I characteristics of the PN Junction diode
PN Junction Diode characteristics are given below
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Written By: Nagapuri Swathi