I-V characteristics of LED

Introduction

The terminals through which an electric current passes are LED or light-emitting diodes. Two terminals that conduct both alternating current and direct current are resistors. A capacitor is a two-terminal device that stores some charge when a DC voltage is applied and does not allow direct current to flow through. A three-terminal device that has three legs is a transistor. 

There are different types of light-emitting diodes available in the market and different LEDs with different wavelengths of light or light intensity. An important feature of LEDs is colour. At the first use of LEDs, it was only red. The use of LEDs has grown with the help of semiconductor processes and new redesigned LED devices, creating different colours.

What is light emission?

The LED-Light emitting diode is an optoelectronic device that is mainly made up of semiconductor material diodes. When the LEDs are forward biassed or the external light is applied, the emission of light occurs. In simple words, we can tell it is used for the conversion of electrical to light energy.

LED semiconductor material

The LED is made up of semiconductor alloy materials like 

• GaP
• GaAsP
• GaAs
• GaN
• ZnS
• ZnTe
• GaInP

The reason behind the usage of these semiconductor materials is they possess the direct bandgap. It gives the radiative light emission. It also provides high efficiency. Along with LED, these semiconductor materials are widely used in visible light, ultraviolet light and infrared light. 

Preparation of semiconductor alloys used for LED

The semiconductor alloys are prepared by two techniques – 

• MOCVD – Metal-Organic Chemical Vapour Deposition
• MBE – Molecular Beam Epitaxy

The semiconductor materials are fabricated and various forms of LEDs are produced. These LEDs possess the characteristics like surface and edge-emitting, resonant cavity, double heterostructure or white light LED.

Structural design of LED

The LED consists of three layers

• P layer
• N layer
• Depletion region.

The P layer has majority carriers called holes and minority carriers called free electrons. The N layer has minority carriers called electrons and majority carriers called holes. The depletion region is the region that opposes the flow of electric current. It is the barrier found between the P and N layer.

The efficient design of LED can be achieved by three methods

• Minority carrier recombination
• Forward biassed generation of minority carriers
• Photon transmission

Working of LED

The  PN junction has a heavily doped N layer and a very thin P layer. The external voltage is applied to both the layers of LED and the light is emitted from the thin P layer. As we already know, the N layer is thicker than the P layer. The major carrier recombination occurs when the depletion region moves towards the thin P layer. The photon is emitted as the result of the recombination process. 

The barrier region contains a certain voltage in it. So, we should apply the external voltage instead. As a result of this, the flow of electric current starts. The electric current turns the LED on. 

Colour of LED

The colour of LED can be varied on the basis of the led semiconductor material used. Different colours are emitted by different semiconductor materials, as listed below.

Light emitted by the LED

The visible and invisible light is emitted from the LED. The visible LED light is used for illumination and display purposes. These are used without photosensors. The invisible LED uses photosensors for illumination. For example, photodiodes.

Merits of LED

• It consumes less energy compared to other optoelectronic devices.
• Its brightness can be easily adjusted by the current variations in the circuit. It helps in using the LED in different conditions or environments.
• It is very cost-effective,  light-weighted, and easily available.
• Its operation is much faster as it is very small in size.
• The emission of different colours is possible in LED
• The usage of toxic materials is avoided during manufacturing. For example, we could see that fluorescent lamps have toxic materials like mercury in them.

Demerits of LED

• The lumination is low in LEDs
• The power requirement is more in LEDs.

Applications of LED

We can find LEDs in most of the devices we use every day like computers, calculators, watches, cameras. It can be found on the laboratory instruments like microprocessors, multimeters and burglar alarming systems. It can be used in traffic signals and lightning aviation.

Conclusion

In this article, we have discussed the LED definition. It is made up of LED semiconductor material with modern techniques. It consists of three layers that are used for the effective functionality of LEDs. The LED light produces many colours along with white light. The LED produced by the advanced methods is used in many applications like illumination, optical communication which includes fibre technology. Apart from this, it is used in many fields. And also, we have covered the advantages and disadvantages of LED, with its applications.