How they work: “Light Emitting Diodes”

With Technology, nothing is impossible. Many times, scientific breakthrough has been achieved in such proportions that, we cannot imagine how life was before such an invention. Once the breakthrough has been accomplished, we do not look back, no body imagines what would happen if such a situation was reversed! In the Solid state, there was the invention of the diode, this volatile semiconductor has been put to many uses, of which, and lighting is the latest and most remarkable! Light emitting diodes, commonly called LEDs, are real unsung heroes in the electronics world. They do dozens of different jobs and are found in all kinds of devices. Among other things, they form the numbers on digital clocks, transmit information from remote controls, light up watches and tell you when your appliances are turned on. Collected together, they can form images on a jumbo television screen or illuminate a traffic light, just name it and you will trace a LED there! Basically, LEDs are just tiny light bulbs that fit easily into an electrical circuit. But unlike ordinary incandescent bulbs, they don’t have a filament that will burn out, and they don’t get especially hot. They are illuminated solely by the movement of electrons in a semiconductor material, and they last just as long as a standard transistor. Many of the LEDs can last for very long. Imagine how long a power indicator on your oven or fridge can last, maybe twenty years or so! A diode is the simplest sort of semiconductor device. Broadly speaking, a semiconductor is a material with a varying ability to conduct electrical current. Most semiconductors are made of a poor conductor that has had impurities (atoms of another material) added to it. The process of adding impurities is called doping. In the case of LEDs, the conductor material is typically aluminium-gallium-arsenide (AlGaAs). In pure aluminium-gallium-arsenide, all of the atoms bond perfectly to their neighbours, leaving no free electrons (negatively-charged particles) to conduct electric current. In doped material, additional atoms change the balance, either adding free electrons or creating holes where electrons can go. Either of these additions makes the material more conductive. A semiconductor with extra electrons is called N-type material, since it has extra negatively-charged particles. In N-type material, free electrons move from a negatively-charged area to a positively charged area. A semiconductor with extra holes is called P-type material, since it effectively has extra positively-charged particles. Electrons can jump from hole to hole, moving from a negatively-charged area to a positively-charged area. As a result, the holes themselves appear to move from a positively-charged area to a negatively-charged area. A diode comprises a section of N-type material bonded to a section of P-type material, with electrodes on each end. This arrangement conducts electricity in only one direction. When no voltage is applied to the diode, electrons from the N-type material fill holes from the P-type material along the junction between the layers, forming a depletion zone. In a depletion zone, the semiconductor material is returned to its original insulating state, all of the holes are filled, so there are no free electrons or empty spaces for electrons, and charge can’t flow. (to be Cont’d) eddie@afrowebs.com