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Physics · 2022 · 3 marks
Semiconductor Electronics: Materials, Devices and Simple Circuitsp-n Junction3 marksUnderstandshort answer
CBSE 2022 · Region 4 · Set 1 · Q5
Answer the following, giving reason: (a) The resistance of a p-n junction is low when it is forward biased and is high when it is reversed biased.…
Answer the following, giving reason:
(a)
The resistance of a p-n junction is low when it is forward biased and is high when it is reversed biased.
(b)
Doping of intrinsic semiconductors is a necessity for making electronic devices.
(c)
Photodiodes are operated in reverse bias.
Marking-scheme solution
a) When a $\displaystyle p-n$ junction is forward biased, the junction width decreases and as a result, its resistance also decreases.
On the other hand, when a $\displaystyle p-n$ junction is reverse biased, the junction width increases hence resistance increases.
b) Conductivity of intrinsic semi-conductors is very low. Hence, no electronic device can be developed using them.
Dopping increases conductivity, hence makes intrinsic semiconductor suitable for making electronic devices.
c) It is easier to observe the change in the current with change in light intensity if a reverse bias is applied.
Alternatively
The fractional change due to photo-effects on the minority charge carriers dominated reverse bias current, is more easily measurable than the fractional change in forward bias current.
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