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LED Lights

The abbreviate form of Light Emitting Diode is LED. LED is a semiconductor diode. A semiconductor material is one whose electrical properties lie in between those of insulators and good conductors. LED is a p-n junction diode that emits inconsistent narrow spectrum light when forward biased. A P-N junction diode is a one-way device offering low resistance when forward-biased and behaving almost as an insulator when reverse-biased. The production of this light is a form of electroluminescence. The emitted light may be in different colors depending upon chemical composition of the semiconducting material used. And sometimes it can be ultraviolet, visible or infrared. In 1955, Rubin Braunstein, who is a scientist born in 1922 and worked in the Radio Corporation of America first reported on infrared emission from GaAs and other semiconductor alloys. And the first practical visible spectrum LED was developed in 1962. It was developed by Nick Holonyak Jr. of the General Electric Company.

A LED is an exceptional type of semiconductor diode. As a Normal diode it consists of a semiconductor material. And also it includes a p-n junction. It is possible to manufacture a single piece of semi-conductor material one half of which is doped by p-type impurity and the other half by n-type impurity. The plane dividing the two halves or zones is called a p-n junction. In a p-n junction the P-side is the anode and the N-side is the cathode. And in diodes current flows from anode to cathode or from P-side to N-side. The current does not transfer in the reverse direction i.e. from cathode to anode or N-side to P-side. An electron is a positive charge carrier and the holes are the negative charge carriers. When it is forward-biased the electrons and the holes are attracted to each other and releases energy. When a normal diode is forward-biased, current flows which causes a voltage drop. The voltage drop times the magnitude of current flow results in power dissipation at the junction. In a normal diode, this power is dissipated in the form of heat energy. However, in the case of LED, this power is dissipated in the form of light.

There are two main differences between normal diodes and LED. One difference is that LEDs are made from gallium arsenide (Ga/As), gallium arsenide phosphide (GaAsP) or gallium phosphide (GaP). Diodes manufactured from these elements radiate visible light energy when forward-biased. The second difference is that LED are so designed as to have a window over the junction so that light energy can be seen.

According to the bandgap energy of the materials forming the p-n junction, the wavelength of the light emitted and also its colour changed. In some diodes the electron-hole recombination is by a non-radiative transition. These are crooked bandgap materials and so they does not produce any optical emission. Silicon and germanium are examples of such diodes. So the materials used for an LED must have a direct bandgap.

LED development began with infrared and red devices. Due to the new inventions of materials in science it makes easy to develop the LEDs with different bandwidths and that of different colors. By the use of variety inorganic semi-conductor materials we can produce different colors of LEDs.