Question: Q. 12. With what considerations in view, a photodiode is fabricated ? State its working with the help of a suitable diagram.
Even though the current in the forward bias is known to be more than in the reverse bias, yet the photodiode works in reverse bias. What is reason?
U [Delhi I, II, III 2015]
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Solution:
Ans. It is fabricated with a transparent window to allow light to fall on diode.
When the photodiode is illuminated with photons of energy $\left(h \nu>E_{g}\right)$ greater than the energy gap of the semiconductor, electron hole pairs are generated. These get separated due to the junction electric field (before they recombine) which produce an emf.
Reason : 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 in the minority carrier current, obtained under reverse bias, is much more than the corresponding fraction change in majority carrier current obtained, under forward bias.
[CBSE Marking Scheme 2015] 1
Ans.
The phitodide works in revorse bius as change in intensity of 1 light is mou detectable in reverse bias. in forwase bias $n»h$ eet $\Delta n$ & $\Delta h$ be the extra $e^{-} &$ holes reated, then $\Delta n=\Delta h$.
[Topper’s Answer 2015]
