Question

An LED is a photodiode which is _______________. 
1. lightly doped and under forward bias
2. heavily doped and under forward bias
3. heavily doped and under reverse bias 
4. lightly doped and under reverse bias

Answer 1

Correct Answer - Option 2 : heavily doped and under forward bias

CONCEPT:

• An LED is a heavily doped P-N junction diode which under forward biased condition emits spontaneous radiations and the wavelength of these radiations falls under wavelength in the visible spectrum.

EXPLANATION:

• When the electric current passed through the LED then the electrons recombine with the holes present in the diode and hence LED emits the light.
• The amount of light emitted will depend on the rate of doping, the diode allows the flow of current only when it is forward biased 
• Hence, the LED has to be forward biased and heavily doped
• Hence, option 2 is the answer.

• Longer life than other electrical light equipments 
• Emits monochromatic light
• Environment friendly