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Application of a forward bias to a p-n junction -
A
Widens the depletion zone
B
Increases the number of donors on the n side
C
Increases the potential difference across the depletion zone
D
Increases the electric field in the depletion zone
Detailed Solution
In forward bias the p-side is connected to the positive terminal and the n-side to the negative terminal of the battery.
The applied voltage opposes the built-in barrier potential, so the effective potential difference across the depletion zone decreases and the electric field in it decreases.
The majority carriers are pushed towards the junction, so the depletion zone becomes narrower; it does not widen.
So the statements about widening of the depletion zone and increase of the potential difference or electric field are all wrong for forward bias.
In forward bias the battery continuously injects electrons into the n-side, so the number of electrons (majority carriers) available on the n side increases and a large current flows.
Hence the answer accepted for this question is that forward bias increases the number of donors (donor electrons) on the n side.
Note: strictly, the number of donor atoms is fixed by doping; the option is accepted in the sense of the supply of majority electrons on the n side.
The applied voltage opposes the built-in barrier potential, so the effective potential difference across the depletion zone decreases and the electric field in it decreases.
The majority carriers are pushed towards the junction, so the depletion zone becomes narrower; it does not widen.
So the statements about widening of the depletion zone and increase of the potential difference or electric field are all wrong for forward bias.
In forward bias the battery continuously injects electrons into the n-side, so the number of electrons (majority carriers) available on the n side increases and a large current flows.
Hence the answer accepted for this question is that forward bias increases the number of donors (donor electrons) on the n side.
Note: strictly, the number of donor atoms is fixed by doping; the option is accepted in the sense of the supply of majority electrons on the n side.