Diode and their characteristics.
Tags: diode, characteristicsofdiode, symbolofdiode, diodeexamples
Published: 2021-07-15 08:28:33

Hi there! Glad to see you. In this post today, I’ll walk you through Diode in detail.
Read the entire post as I’ll discuss each and everything related to Diode such as Diode definition, characteristics, working, symbol, types, and applications.
Let’s get started.
##Definition:
A [diode](https://www.theengineeringprojects.com/2018/05/introduction-to-diode.html) is a device in which current flows in one direction only. It is a one-way electronic valve that comes with two terminals named anode and cathode. The anode pin is a positive terminal and the cathode pin is a negative terminal and the device allows the current to flow from the anode pin to the cathode pin and it shows maximum resistance for the current to flow in the opposite direction.
##Symbol:
The electrical symbol of the diode is shown below.
![Alt Text](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/4r14gh5j621tmso6fdej.png)
###Diode Working:
The diode device carries two junctions: the N junction and the P junction. And the working of the diode is mainly dependent on the interaction between these two junctions. The N junction is an area that comes with a high concentration of electrons and the P junction is an area that comes with a high concentration of holes. 
The diode working can be explained using the following three conditions. 
###Forward Biased Diode:
In this forward biased condition, the N side of the diode is connected with the negative source terminal and the P side is connected with the positive source terminal as shown in the figure below. 
![Alt Text](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/5x2qg1kthxxqxpn5getb.png)

There will be no current flow in the diode when we increase the source voltage from zero. The zero current is due to the availability of the potential barrier. But when we increase the applied voltage above the forward potential barrier the diode will start acting as a short-circuited path and the current resistance occurs due to the external resistors. 
###Reverse Biased Diode:
This condition is opposite to the forward biased condition. In this condition the diode is connected with the power supply in reverse order i.e. the N side is attached with the source positive terminal and the P side is connected with the source negative terminal. 
![Alt Text](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/srlqkjjflom5y6mwl9q6.png)
In the reverse biased condition, there is an electrostatic attraction in the depletion region that allows the holes in the P region to move away from the depletion region, leaving more uncovered negative ions. Know that, in this case, the current flow through the circuit is zero.
###Unbiased PN-Junction Diode:
Unlike the two conditions mentioned above, there is no voltage applied from the external source in the unbiased [PN junction](https://byjus.com/physics/p-n-junction/). However, when you combine both N and P junctions, it allows the electrons to flow from the N material to the P material, and consequently, the holes will flow from the P side to the N side. 
![Alt Text](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/osaomwb8bhgpwa4s4w74.png)
This flow of electrons and holes will produce the third region called the depletion region where no charge carriers are involved. 
##Diode Characteristics:
* The current-voltage curve is used to define the characteristics of the diodes. We take voltage on the x-axis and current on the y-axis and will measure the respective voltage for a certain amount of current. The V-I relation is linear in the case of resistors but for diodes it is different. The diode V-I curve is shown in the below figure. 
![Alt Text](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/c3vk4ktxf62e03isf2yr.png)
The diode works in three regions according to the voltage applied across it. 
Forward Bias Region: When the voltage across the diode is positive, the current starts flowing through it, and the device will be turned ON. This is the forward bias region, and for the current to flow in this region, the positive voltage must higher than the forward voltage Vf. 
* Reverse Bias Region: In the reverse bias region the forward voltage Vf is more than the applied voltage while the applied voltage is more than the breakdown voltage and the device will be turned OFF. In this scenario, the current flow is minimum as the device shows the maximum resistance but a small current flow will occur in this condition, called reverse saturation current. 
Breakdown Region: In the breakdown region the flow of current is in the reverse direction (from cathode terminal to anode terminal) when the very high negative voltage is applied to the device. 
##Types of Diode: 
The different types of diode include:
* Photodiodes:
Photodiodes are light sensitive and are widely used in optical communication and solar cell applications. They come in a material where light can easily pass through them. Multiple diodes can be packaged in a single device to form a linear or two-dimensional array.
* Zener Diodes:
Normally, the diode conducts in forward biased condition, however, in the case of the Zener diode, the scenario is different. Zener diode conducts in reverse bias conditions. The breakdown voltage of the Zener diode is less than 5V and they are generally called reverse breakdown diodes. The Zener diode is a heavily doped semiconductor device that forms a thin deletion region that results in increasing the electric field intensity.
* Crystal Diodes:
Crystal diodes are also known as point contact diodes where anode pin is comprised of thin metal and cathode pin is made up of semiconductor crystal material. These diodes are not so common and are also known as Cat’s Whisker diodes. 
* PIN Diodes:
PIN diodes are used as frequency switches and attenuators and they carry an un-doped central layer due to the p-type/intrinsic/n-type structure. These diodes can endure high voltages and are a right match for power electronics applications. 
* Avalanche Diodes:
Avalanche diodes are identical to Zener diodes, however, there is one difference i.e. both diodes contain temperature coefficients of different polarities. The current starts flowing in these diodes in the reverse direction when the reverse-biased voltage exceeds the breakdown voltage.  
* LED Diodes:
LED diodes, also called low-efficiency diodes, are electric devices that are capable of emitting light of different colors like red, orange, blue, and green. The color of the emitted light depends on the crystalline substance used in the device. These diodes are mainly employed in signal applications due to their light-emitting capability. 

###Diode Applications:
The applications of the diodes include:
* Incorporated to control the current flow
* Used for temperature measuring applications
* Used for demodulation of the amplitude signal
* Employed as a waveform clipper
* Employed in the making of rectifiers for converting AC signal to DC signal
That’s all about the diode. Hope you’ve enjoyed reading this article. If you have any queries, you can approach me in the section below where I’ll answer your questions the best way I can. Thank you for your precious time.