Question

Identify the incorrect statement :

• A. when a P-N junction diode is forward biased, the width of the depletion region decreases.
• B. when a P-N junction diode is reverse biased, the barrier potential increases
• C. a photon diode is operated in the reverse bias
• D. an LED is a lightly doped P-N junction diode which emits spontaneous radiation of forward biasing.

Answer 1

The Correct Option is D

• LEDs are heavily doped: They are designed with heavy doping to increase recombination efficiency and light emission.
• Correct description: LEDs emit spontaneous radiation under forward bias, but the doping is intentionally heavy, not light.

Why other options are correct:

• A: Forward bias reduces the depletion width by neutralizing the barrier potential.
• B: Reverse bias widens the depletion region and increases the barrier potential.
• C: Photodiodes operate in reverse bias to detect light by measuring leakage current.

Key Point: The error in D lies in the "lightly doped" claim, which contradicts standard LED design principles.

Answer 2

Let's analyze each statement:

"when a P-N junction diode is forward biased, the width of the depletion region decreases." - This statement is correct. Forward bias reduces the potential barrier, allowing more majority carriers to cross the junction, thus shrinking the depletion region.

"when a P-N junction diode is reverse biased, the barrier potential increases." - This statement is correct. Reverse bias increases the potential difference across the junction, widening the depletion region and increasing the barrier potential.

"a photon diode is operated in the reverse bias." - This statement is correct. Photodiodes are designed to detect light and are operated in reverse bias to minimize dark current and improve sensitivity.

"an LED is a lightly doped P-N junction diode which emits spontaneous radiation of forward biasing." - This statement is incorrect. LEDs are heavily doped P-N junction diodes. Heavy doping is crucial for efficient radiative recombination, where electrons and holes combine and release energy in the form of photons (light). Lightly doped diodes are not efficient at this process.

Therefore, the incorrect statement is: "an LED is a lightly doped P-N junction diode which emits spontaneous radiation of forward biasing."

Final Answer: The final answer is ${\text{"an LED is a lightly doped P-N junction diode which emits spontaneous radiation of forward biasing."}}$