Light Emitting Diode (LED)

Light Emitting Diode (LED) Points : light emitting diode (led), Definition The basic operation of the LED is shown in the figure. The LED is a PN-junction diode and work when forward biased. When a small forward biased voltage is applied, it causes a current to flow across the junction. Electrons in the N-region and holes in the P-region flow toward the junction where they recombine and release some energy. The recombination continues as long as the voltage is applied. In Silicon and Germanium semiconductors, the released energy is dissipated as heat. While in the LEDs, the released energy appears as photon of light. The semiconductor materials used for LEDs in fiber optic systems arc gallium aluminum arsenide or gallium arsenide. Other semiconductor compound used to make LEDs is gallium-arsenide-phosphide and indium-gallium-arsenide- phosphide. GaAs LEDs emit near 930 nm. While GaAIAs emit light at wavelengths of 750 to 900 nm. GaAsP emits visible red light at 665 nm.

In simple LEDs light is emitted from the surface in all directions and can be concentrated Into a narrow angle by making the internal structure of the LED more complex. One way to make the emitted light more directional is to etch a hole in the substrate and is called Burrus diode. The light from the Burrus diode is collected by inserting a fiber into the hole.

Another configuration is the edge-emitting diode, in which the top and bottom of the diode is cover with electrical contacts to avoid the emission of light from there. The emission of light is confine to a thing narrow strip at the junction.