LED explanation

 LED

The LED is an optical diode, which emitter light when forward biased. The symbol of LED which is similar to P-N junction diode apart from the two arrows indicating that the device emits the light energy. 

                              Symbol of LED 

Operation of LED

When p-n junction is forward biases the electrons cross the p-n junction from the ntype semiconductor Material and recombination with the holes in the p type semiconductor Material. The free electrons are in the conduction band. While the holes are present in the valance band. Thus the free electrons are at higher energy level with respect to the holes. When free electrons recombination with hole, it falls from conduction band to a valance band. The energy corresponding to the difference between higher level and lower released by an electron while traveling from the conduction band to the valance band. In normal diodes,this energy released is in the formof photons which emits the light energy. Hence such diodes are called light emitting diodes. This process is called "electroluminescence".

The basic principle of this process the energy released in the form of light depends on the energy corresponding to the forbidden gap.this determines the wavelength on the emitted light .the wavelength determines the colour of the light and also determines whether the light is visible or invisible.

Materials and colors

The LED  use mixtures of gallium ,arsenic, phosphorus. 

Construction of LED 

One the methods used for the LED  construction is to deposite three semiconductor layers on the substrate. In between p type and n t pe.there exists an active region. This active region emits light, when an electron and holes recombination. When the diode is forward biased, holes from p type and electrons from n type,both get driven into the active region and  when recombination the light emitted.

In the particular structure the LED emits light all the way around the layered structure. The basic layers structure is placed in the tiny reflection cup so that the light from the active layers.

Advantage of LED

1.light weight

2.available in various colors

3.long life

4.cheap

5.easy to interface 

6.fast operating device

Disadvantages of LED

1.large power can need

2. High efficiency 

3.less current can take

Application of LED 

1.optocouplers

2.remote control device

3.displays

4.on off indicators