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p-n Junction under Forward Bias
Concepts tested here
- Effect of forward bias on the junction
All Questions
2005 AIPMT 1 question
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Application of a forward bias to a p-n junction -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.