An LED or light emitting diode is an optoelectronic device, which can emit light when it is properly biased. The early light emitting diodes used to emit a light beam of rather low intensity, but the modern ones make up for this set back by proper illumination or emission of light. The light emitted by modern LED's are in numerous wavelengths, and hence they offer a wide range of colors for us to choose from. The main advantages of LED's are their limited power consumption and very high efficiency. They are pretty robust, rugged and tough enough to withstand mechanical shocks given to them, they have a very quick switching response and they are very compact.
A light emitting diode is almost similar in construction to a pn diode; the light emitting diode is made of a semi-conducting material such as silicon or germanium, which is doped with p-type and n-type impurities in order to get a pn formation. The LED usually consists of the following parts, an epoxy lens or case to cover the semi conducting material, wire bonds, reflective cavity, semi conductor die and anvil post which is also known as the lead frame.
When a potential is applied to this device a current flows through the junction resulting due to the recombination of the holes and electrons, the recombination results in the release of energy in the form of light photons.
The production of the LED's actually began with red and infrared devices, which contained gallium arsenide. Now many ranges of colors are available when we look for a particular type of LED. Advancements in material science and physics have lead to the manufacture of LED's with wavelengths shorter then ever.
The light emitting diodes are built upon an n- type substrate with an electrode attached to the p- type layer deposited on the surface. Sapphire substrate is of common use in modern light emitting diodes. Most of the materials for the manufacture of light emitting diodes have a high index of refraction. Much light is reflected at the material air surface interface.
The usual red LED's most of us have come across are made up of gallium arsenide phosphide, the orange ones can also be made up of the same material, zinc selenide is used for the manufacture of blue LED's, in this way many chemical compounds form the raw materials for the manufacture of LED's of different colors.
Next time you use an LED, now you know what they are made of!