Mention the important considerations

cbse
semiconductor

#1

Mention the important considerations required while fabricating a p-n junction diode to be used as a Light Emitting Diode (LED). What should be the order of band gap of an LED, if it is required to emit light in the visible range?


#2

For LEDs, the threshold voltages are much higher and slightly different for different colours.
The reverse breakdown voltages of LEDs are low generally around 5 V. It is due to this reason, the care is taken that high reverse voltages do not appear across LEDs. (1) There is very little resistance to limit the current in LED. Therefore, a resistor must be used in series with the LED to avoid any damage due to the high current to it. (1) The semiconductor used for fabrication of visible LEDs must adeast have a band gap of 1.8 eV (spectral range of visible light is from about 0.4 |lm to 0.7 |Xm, i.e. from about 3 eV to 1.8 eV).