Question

LEDs are based on the principle of

• A. Forward bias
• B. Eletro- luminescence
• C. Photon sensitivity
• D. Electron-hole recombination

Hint:

LEDs emit light due to electroluminescence, which occurs during the radiative recombination of electrons and holes at a forward-biased p-n junction.
The color of light emitted depends on the semiconductor material and its bandgap energy.
LEDs require forward bias to operate.

Answer 1

The Correct Option is B

Light Emitting Diodes (LEDs) are semiconductor devices that emit light when an electric current passes through them. The underlying principle is electroluminescence. Electroluminescence is an optical and electrical phenomenon in which a material emits light in response to the passage of an electric current or to a strong electric field. In an LED:
The p-n junction is forward biased (Option a - this is a condition for operation, not the fundamental principle of light emission itself).
Under forward bias, electrons from the n-side and holes from the p-side are injected into the depletion region and then into the opposite regions (minority carrier injection).
These injected minority carriers recombine with the majority carriers (Option d - this is the process that leads to light emission).
During this recombination process, electrons transition from a higher energy level (conduction band) to a lower energy level (valence band), releasing energy. In direct bandgap semiconductors used for LEDs, this energy is emitted in the form of photons (light). Option (b) "Electroluminescence" is the overarching principle describing light emission due to electric current. Option (d) "Electron-hole recombination" is the specific mechanism within the semiconductor that results in electroluminescence. Option (a) "Forward bias" is the necessary operating condition. "Photon sensitivity" (Option c) describes photodetectors (like photodiodes), not light emitters like LEDs. Given the options, electroluminescence is the most appropriate answer for the "principle" on which LEDs are based. The recombination is the physical process causing it. \[ \boxed{\text{Electroluminescence}} \]