![]() Switching Time: The Switching time of LEDs is in order of 1ns.Temperature Range: It can be operated over a wide range of temperature ranging from 0 0C -70 0C.The output characteristics curve shows that radiant power of LED is directly proportional the forward current in LED. The characteristics curve of the LED shows that the forward bias of 1 V is sufficient to increase the current exponentially. If it will operate in reverse biased it will get damage as it cannot with stand reverse voltage. LED is operated in forward biased mode only. If the semiconductor material is translucent, the light will be emitted from the junction as junction acts as the source of light. ![]() The electrons in these compounds lose their energy by emission of photons. emit light when electrons-holes recombine. Thus, semiconductor compounds such as Gallium Phosphide (Gap), Gallium Arsenide (GaAs), Gallium Arsenide Phosphide (GaAsP) etc. Thus, they are not used for LEDs as we want semiconductor in which electrons lose their energy in the form of light. The electrons in Silicon and Germanium lose their energy in the form of heat. The electrons can lose their energy either in the form of heat or light. Thus, if electrons tend to recombine with holes they have to lose some part of the energy to fall in lower energy band. The energy level of the Conduction band is higher than the energy level of the Valence band. The electrons of N-type are in the conduction band and holes of P-type are in the valence band. The electrons are majority carriers in N-type and holes are majority carriers in P-type. If any significant part of radiated light tends to hit bottom surface then that will be reflected from the bottom surface to the device top surface. The gold-film layer on N-type also provides reflection from the bottom surface of the diode. Similarly, Gold-film layer is coated on N-type to provide cathode connection. The metal film is used on the P-type layer to provide anode connection to the diode. On the other hand in N-type region, the epitaxial layer is grown on N-type substrate. The P-type layer is formed from diffusion of semiconductor material. This is the reason that P-type is placed above. If P-type will be placed below the light will be emitted from the surface of P-type but we will not be able to see it. ![]() Besides, it is the surface of the device, thus, the light emitted can be easily seen on the surface. The semiconductor layer of P-type is placed above N-type because the charge carrier recombination occurs in p-type. In addition to it, the ranges of typical forward voltage are also given below. ![]() Below are some of the material and their respective colour of light which they emit. Any of the above-mentioned compounds can be used for the construction of LED, but the colour of radiated light changes with the change in material. The semiconductor material used in LED is Gallium Arsenide (GaAs), Gallium Phosphide (GaP) or Gallium Arsenide Phosphide (GaAsP). The symbol of LED is described in the diagram below, the same symbol is used in electronics circuits. Now, the question arises how the semiconductor material in LED emits light? The answer to this question lies in the construction and working of LED.
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