PN junction Diode plays a vital role in our electronic fields, because of their unique property (current flows in only one direction) they are used in many electronic or electrical circuits like rectifiers, switches, clippers, clampers, voltage multipliers.
In this article, we will learn about what is a PN Junction Diode and how it Works and also effect on PN Junction diode with different modes and I am sure this article will help you a lot to understand about Diode.
After completing this article you will be able to:
- Understand the PN Junction Diode.
- Understand the Working of PN Junction Diode.
- Understand the Effect of Forward Bias and Reverse Bias on PN Junction Diode.
- Understand the V-I Characteristics of PN Junction Diode.
- Understand the Practical Applications of PN Junction Diode.
What is PN Junction (Diode):
A PN Junction Diode is a two-terminal semiconductor device. It’s made up from a small piece of semiconductor material (usually Silicon), it allows the electric current to flow in one direction while opposes the current in other direction. In the Forward Bias, the diode allows the current to flow in uni-direction. On the other hand, when the diode is reverse biased it opposes the electric current to flow. A PN Junction Diode is a semiconductor device with two opposite region such as (P-type region and N-type region).
- The P-region is called as the anode and is connected to a positive terminal of a battery and it has Holes in majority carrier and electrons in minority carrier.
- The N-region is called as the cathode and is connected to the negative terminal of a battery and it has Electrons as a Majority carrier while holes as Minority carrier.
When the P-type semiconductor material is joined with the N-type semiconductor material, a P-N Junction is formed, hence resulting P-N Junction is also called as a P-N Junction Diode.
The basic diode structure and symbol of PN Junction Diode is shown in the figure below.
Biasing of Diode:
Biasing means applying external voltages to the device, biasing of a diode is of two types: Forward Biasing and other one is Reverse Biasing.
Forward Biasing of Diode: We connect positive terminal of the battery to the P-type Material and Negative terminal of the battery to the N-type, hence this configuration is called as Forward Bias Configuration of Diode. In this configuration Diode allows the current to flow in uni-direction.
Reverse Biasing of Diode: We connect Negative Terminal Battery to the P-type Material and Positive terminal of Battery to the N-type Material, hence this configuration is called as Reverse Bias configuration of Diode. In this configuration, diode does not allow the flow of current.
Forward Bias of PN Junction Diode:
Forward bias is the condition that allows current through the PN junction Diode. The voltage source is connected in such a way that it produces a Forward Bias. This external bias voltage is designated as V(bias). The resistor limits the forward current to a value that will not damage the diode.
Note that the -ve side of VBIAS is connected to the n-region of the diode and the +ve side is connected to the p-region. This is one requirement for forward bias.
A second requirement is that the bias voltage, V(bias), must be greater than the barrier potential.
What is Barrier Potential of PN Junction Diode?
A Barrier Potential is an internal potential a semiconductor material, in case of Silicon-based PN Junction diode it is 0.7v and in case of Germanium, it is 0.3v. It means in order to forward bias the PN junction diode V(bias) should be greater than 0.7 for silicon and 0.3V for germanium.
As we know the N-type material is consist of Electrons and the P-type material is consist of Holes.
A fundamental picture of what happens when a PN junction diode is forward-biased is shown below. When the P-type material is connected with a positive terminal of battery it transfers the holes (positive charge carrier), which travels from p-type material to the N-type material through (Junction).
When the N-type material is connected with a negative terminal of battery it transfers the free electrons (negatively charged carriers), which travels from n-type material to the P-type material through (junction).
These free electrons are attracted towards the positive terminal of the diode while the holes are attracted towards the negative terminal of a diode.
Reverse Bias of PN Junction Diode:
Reverse bias is the condition that essentially prevents current through the PN junction diode. As mentioned above if we connect -ve terminal of the battery to P-type material and +ve Terminal of Battery to N-type material this lead to the diode in Reverse Bias. note that the depletion region is shown much wider than in forward bias.
A diode connected for reverse bias. A limiting resistor is shown although it is not important in reverse bias because there is essentially no current.
An illustration of what happens when a PN junction diode is reverse-biased is shown below. When the P-type material is connected with a negative terminal of a battery, the holes are attracted away from the junction and attracted to the negative electrodes of batter.
Similary when the N-type material is connected with a positive terminal of a battery, the free electrons are attracted away from the junction and attracted towards the positive electrodes.
This results in an increase in the depletion region. As the depletion region widens, the availability of majority carriers decreases. As more of the n- region and p-regions become depleted of majority carriers, the high potential barrier is created thus opposing electric current to flow in reverse bias.
Note: if the reverse bias voltage is increased up to a high value, it will damage the PN junction diode.
V-I CHARACTERISTIC OF A PN junction Diode:
As you have learned, forward bias produces the current through a PN junction diode and reverse bias essentially prevents current, except for a negligible reverse current. Reverse bias prevents current as long as the reverse-bias voltage does not exceed the breakdown voltage limit of the junction. Now we will examine the relationship between the voltage and the current in a diode on a graphical basis.
Effect of Forward Bias on V-I Characteristics of PN Junction Diode:
When a forward-bias voltage is applied across a diode, there is current. This current is called the forward current.
When the forward-bias voltage is increased to a value where the voltage across the diode reaches approximately 0.7 V (barrier potential), the forward current begins to increase rapidly, as illustrated in Figure given below. As you continue to increase the forward-bias voltage, the current continues to increase very rapidly, but the voltage across the diode is constant till 0.7v for silicon and 0.3v for germinium.
Effect of Reverse Bias on V-I Characteristics of PN Junction Diode
When a reverse bias is applied across a PN junction diode, there is an extremely small reverse current (IR) through the PN junction due to minority carriers.
Once the applied bias voltage is increased to a value where the reverse voltage across the diode reaches the breakdown value of the diode which is (VBR), the reverse current begins to increase rapidly. As you further increase the bias voltage, the voltage across the diode increases above Breakdown, and diode become damaged, thus it’s not a normal mode of operation for most PN junction devices.
Complete V-I Characteristics on PN Junction Diode
Combine the curve for both forward bias and reverse bias, and you have the complete V-I characteristic curve for a PN junction diode, as shown in Figure give below.
Applications of PN Junction Diode:
- PN Junction Diodes are mostly used for rectification (Alternative Current to Pulsating DC).
- They are used as clipper to clip the portion of AC.
- They are used as clamper to change the reference voltage.
- They are used as switches in many electronic circuitry.
- They are used in Voltage Multipliers to increase the output voltage.
- They are used in power supplies.
There are Many different types of PN Junction Diode, and we have covered all of them check out the working of different types of diodes:
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