Question:
A light emitting diode (LED) emits light when it is ____} biased. A photodiode provides maximum sensitivity to light when it is ____ biased.
A light emitting diode (LED) emits light when it is ____} biased. A photodiode provides maximum sensitivity to light when it is ____ biased.
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Remember: {Emit} needs injection \(\Rightarrow\) forward bias (LED). {Detect} needs swift carrier separation \(\Rightarrow\) reverse bias (photodiode).
Updated On: Sep 1, 2025
- forward, forward
- forward, reverse
- reverse, reverse
- reverse, forward
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The Correct Option is B
Solution and Explanation
Step 1: LED operation
An LED emits photons via radiative recombination across the p–n junction. This requires forward bias so that carriers (electrons/holes) are injected into the junction in sufficient numbers to recombine and emit light.
Step 2: Photodiode operation for maximum sensitivity
A photodiode detects light by generating electron–hole pairs in/near the depletion region. Under reverse bias (photoconductive mode), the depletion width increases and the electric field sweeps the carriers quickly, giving:
- higher quantum efficiency/sensitivity,
- lower junction capacitance \(\Rightarrow\) faster response,
- reduced recombination losses.
Final Answer: LED—forward biased; Photodiode—reverse biased \(\Rightarrow\) (B).
An LED emits photons via radiative recombination across the p–n junction. This requires forward bias so that carriers (electrons/holes) are injected into the junction in sufficient numbers to recombine and emit light.
Step 2: Photodiode operation for maximum sensitivity
A photodiode detects light by generating electron–hole pairs in/near the depletion region. Under reverse bias (photoconductive mode), the depletion width increases and the electric field sweeps the carriers quickly, giving:
- higher quantum efficiency/sensitivity,
- lower junction capacitance \(\Rightarrow\) faster response,
- reduced recombination losses.
Final Answer: LED—forward biased; Photodiode—reverse biased \(\Rightarrow\) (B).
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