Light emitting diode (LED) is a diode that emits light when a current passes through it in the forward direction. It is a very useful display device. LED’s are available which emit light in different colors like red, green, yellow. orange and white.
Construction Of Light Emitting Diode
LED is a P-N junction diode. It is made up of gallium arsenide (GaAs) or gallium phosphide (GaP) or gallium arsenide phosphide (GaAsP). Metal contacts are made both on P and N side for external connection to the battery. The conducting surface connected to the P-material is much smaller. to permit the emergence of maximum light. LED is a direct band gap type diode
Working Principle Of Light Emitting Diode
The when an electron is excited from the valence band to the conduction band, the electron and hole pairs are created as
shown in Figure 4.12. Electron stays in conduction band for a very short period called life time109 sec) and then return back. In the transition from higher energy state (conduction band, Ec) to lower energy state (valence band, Ev) these electrons they Energy released Eg Ec Dy and the associated frequency of radiation, f-constant. In all semiconductor diodes, some of this energy will be given off as heat and some in the form of light photons. In silicon and germanium, the greater percentage is given off in the form of heat and emitted light is negligible. In other material such as gallium arsenide (GaAs), gallium phosphide (GaP) and gallium arsenide phosphide (GaAsP) the number of photons of light energy is sufficient and their frequency lies in a visible
range, therefore, light is visible in LED Where he is planks. Figure 4.12 shows that the recombination of holes and electrons results in emitted light at the site of
recombination. The intensity of light depends upon a number of recombination, which is proportional to the
forward current in the diode. Therefore, the intensity of light depends upon the forward current through
Applications Of Light Emitting Diode
- LED is designed so as to produce coherent light with a very narrow bandwidth. The resulting called LASER diode and find application in an optical communication system and in the CD.
- As an optoisolator (combination of LED and Photodiode in the same package).
- In display devices player.