JEE Main 2025 Jan 24 Shift 1, Physics Q6: Semiconductors, p-n Junction Diode and Applications
Consider the following statements :
A. The junction area of solar cell is made very narrow compared to a photo diode.
B. Solar cells are not connected with any external bias.
C. LED is made of lightly doped p-n junction.
D. Increase of forward current results in continuous increase of LED light intensity.
E. LEDs have to be connected in forward bias for emission of light.
- A
B, D, E Only
- B
A, C Only
- C
A, C, E Only
- D
B, E Only
Evaluate each statement against standard device physics:
A. False. The junction (illuminated) area of a solar cell is made large, not narrow, to maximise photon collection. A photodiode is the one with a small active area for fast response.
B. True. Solar cells operate without any external bias; they generate their own voltage from incident light (photovoltaic mode).
C. False. LEDs use heavily doped p-n junctions so that radiative recombination occurs efficiently in a narrow region near the junction.
D. False. LED light intensity rises with forward current only up to a point. Beyond a threshold, efficiency drops ("efficiency droop") and excess current produces heat, eventually damaging the device. The increase is not continuous indefinitely.
E. True. An LED emits light only when forward biased (carriers are injected across the junction and recombine radiatively).
Correct statements: B and E. Option (4).
Concept behind this question
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