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What is Diode? A Detailed Guide on Diodes

In this post today, I’ll cover Diode in detail, including Diode definition, symbol, working, characteristics, types, and applications.

Let’s jump right in.


A diode is an electrical device that allows the current to flow in one direction only and shows maximum resistance for the current to flow in the opposite direction. A diode carries two terminals called anode and cathode. The anode is a positive terminal and the cathode is a negative terminal and the current will only flow from the anode terminal to the cathode terminal.


The following figure shows the electrical symbol of the diode.the electrical symbol of the diode


The working of the diode depends on the interaction between the P and N junction. The P junction is a region that contains a high concentration of holes while the N junction is a region that contains a high concentration of electrons.

To understand the working of the diode we’ll take three following conditions.

A: Forward Biased Diode:

Forward biased condition will occur when the P-type material of the diode is connected with the positive terminal of the source and the N-type material is connected with the negative terminal of the source.

Workings of a Forward Biased Diode

At first, when we increase the voltage from zero, no current will flow through the diode due to the presence of a potential barrier. However, when the applied voltage exceeds the forward potential barrier, the diode will behave as a short-circuited path and the current flow will be resisted by the external resistors.

Reverse Biased Diode:

This condition will occur when the P-type material of the diode is connected to the negative terminal of the source and the N-type material is connected to the positive terminal of the source.

Workings of a Reverse Biased Diode

In this condition, the holes present in the P region will shift further away from the depletion region due to electrostatic attraction. As a result, more uncovered negative ions will be left behind. In this scenario, there will be no current flow in the circuit.

Unbiased PN-Junction Diode:

In unbiased conditions, there will be no voltage applied from the external energy source. When the P and N junctions are attached, it results in the flow of electrons from the n-type material to the p-type material, and the flow of holes from p-type material to the n-type material.

Workings of an Unbiased PN-Junction Diode

This flow of charge carriers will generate the third region where no charge carriers are present, this third region is called the depletion region.


The characteristics of the diodes can be demonstrated by the current-voltage curve. This means, for a certain amount of current we’ll measure the respective voltage across it. The resistors show the linear V-I relationship, however, in the case of diodes this relationship is different. The following figure shows the V-I curve of the diode.

Characteristic graph of a diode: current-voltage

The diode operates in three different regions based on the voltage applied across it.

  • Forward Bias Region: When the positive voltage is applied across the diode, the diode will be turned ON and the current will pass through it. To flow the current through the diode in the forward bias region, the positive voltage should exceed the forward voltage Vf.
  • Reverse Bias Region: In this region, the diode will be turned OFF and the applied voltage will be less than the forward voltage Vf and more than the breakdown voltage Vbr. In this condition, the device shows the maximum resistance for the current, however, a very small amount of current will flow through the diode called reverse saturation current.
  • Breakdown Region: When a very large and negative voltage is applied across the diode, it will allow the current to flow in a reverse direction from cathode to anode. This region is called the breakdown region.


The diodes are divided into the following different types.

Zener Diodes:

Zener diodes are heavily doped semiconductor devices that conduct in reverse bias conditions. They are also known as reverse breakdown diodes and come with breakdown voltage below 5V. Because of the presence of heavily doped semiconductor material, the Zener diode constitutes a very thin depletion region to increase the electric field intensity.


Photodiodes are the right match for solar cells and optical communication applications because they can sense light and are mostly packaged in a material that allows the light to pass through it. A range of photodiodes can be incorporated in a single device either as a two-dimensional array or as a linear array.

Avalanche Diodes:

Avalanche diodes are similar to Zener diodes with one difference i.e. both come with a temperature coefficient of different polarities. These diodes start conducting in the reverse direction when the reverse-biased voltage surpasses the breakdown voltage. At a certain reverse voltage, these diodes break down without being destroyed.

Crystal Diodes:

These diodes are point contact diodes. They contain a semiconductor crystal material for cathode, and the anode is made up of thin metal. These diodes are also called Cat’s Whisker Diode and are not easily available in the market.

LED Diodes:

LED diodes contain a crystalline substance that can emit light in different colours including orange, red, green, and blue, based on the crystalline substance used in the diode. These diodes are widely used in signal applications and are called low-efficiency devices.

PIN Diodes:

PIN diodes are widely used in power electronics because they can bear high voltages. A PIN diode contains a p-type/intrinsic/n-type structure because of an un-doped central layer. They are frequently employed as attenuators and frequency switches.


The diodes are used in the following applications.

  • Used as a waveform clipper
  • Used to control the flow of current
  • Incorporated for demodulation of the amplitude signal
  • Employed for temperature measuring applications
  • Used in the construction of rectifiers to convert AC signal to DC signal

Hope you’ve found this article helpful. If you have any questions, you can leave your comment in the section below. I’d love to help you the best way I can. Thank you for reading the article.

HI, I am a student of Electrical Engineering. I am currently working for an electronic store. I work at the electrical components there. I am learning many useful practical concepts there. On the other hand, I give online tuitions to some students of high school I love electrical and electronics devices and have a plan to have a Master's Degree in Electronics.