9.0 Light emitting diode (LED)

  Semi-conductor Devices and Electronics

Light emitting diode (LED) converts electrical energy into light energy.

Note:

• It is a heavily doped $p-n$ junction which under forward bias emits spontaneous radiation.
• The $I-V$ characteristics of a LED is similar to that of $Si$ junction diode. But the threshold voltages are much higher and slightly different for each color.
• The reverse breakdown voltages of LED is approximately $5\ V$.
• The semiconductor used for fabrication of visible LEDs must at least have a band gap of $1.8\ eV$.
• The compound semiconductor gallium arsenide phosphide $(GaAsP)$ is used for making LEDs of different colors.
• $GaAs$ is used for making infrared LED.
• The symbol of a LED is as shown in the figure.

Uses of LED

1. Indicators and signs
2. General lighting
3. Display screen
4. Electronic equipments
5. Back light sources