Light emiting diodes

Today”s world life LED is very important in our life.In every field of electronics instrument led is using like screens electric bulbs etc.Because of LED’s instruments will help to saves energy and money. and to much interesting features are for LED instruments like much efficiency,long lasting compare to other instruments in the same field. Nick Holonyak who he came up with the idea of the light-emitting diode in 1962 while he was working for the General Electric Company.Nick Holonyak (born November 3 1928) is an american electrical engineer.

An LED is a special type of diode.So first we want to go through whats is a diode?

Diodes
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Diodes is a two terminal electronics instrument. Diaod is a semiconductor device. It allows current to flow only in one direction and blocks the current that flows in the opposite direction. The two terminals of the diode are called as anode and cathode.

The diode operates when a voltage signal is applied across its terminals. The application of a DC voltage to make the diode operate in a circuit is called as Biasing. As already mentioned above the diode resembles to that of a one way switch so it can either be in a state of conduction or in a state of non conduction. The ‘ON’ state of a diode is achieved by ‘Forward biasing’ which means that positive or higher potential is applied to the anode and negative or lower potential is applied at the cathode of the diode. In other words, the ‘ON’ state of diode has the applied current in the same direction of the arrow head. The ‘OFF’ state of a diode is achieved by ‘Reverse biasing’ which means that positive or higher potential is applied to the cathode and negative or lower potential is applied at the anode of the diode. In other words, the ‘OFF’ state of diode has the applied current in the opposite direction of the arrow head.During ‘ON’ state, the practical diode offers a resistance called as the ‘Forward resistance’. The diode requires a forward bias voltage to switch to the ‘ON’ condition which is called Cut-in-voltage. The diode starts conducting in reverse biased mode when the reverse bias voltage exceeds its limit which is called as the Breakdown voltage. The diode remains in ‘OFF’ state when no voltage is applied across it.

A simple p-n juction diode is fabricated by doping p and n type layers on a silicon or germanium wafer. The germanium and silicon materials are prefered for diode fabrication because of They are available in highly purified state.Slight doping like one atom per ten million atoms of a desired impurity can change the conductivity to a considerable level.The properties of these materials change on applying heat and light and hence it is important in the devlopment of heat and light sensetive devices.

Working of LED
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When a diode is forward-biased so that electrons and holes are zipping back and forth across the junction, they are constantly combining and wiping one another out. Sooner or later, after an electron moves from the n-type into the p-type silicon, it will combine with a hole and disappear. That makes an atom complete and more stable and it gives off a little burst of energy in the form of a tiny “packet” or photon of light.

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