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Semiconductor Electronic: Material, Devices And Simple Circuits — Physics STD 12 Science — Question

Gujarat BoardEnglish MediumSTD 12 SciencePhysicsSemiconductor Electronic: Material, Devices And Simple Circuits3 Marks
Question
With what considerations in view, a photodiode is fabricated? State its working with the help of a suitable diagram. Eventhough 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 the reason?
✓

Answer


It is fabricated with a transparent window to allow light to fall on diode.
When the photodiode is illuminated with photons of energy $(hv > E_g)$ greater than the energy gap of the semiconductor, electron - holes pairs are generated. These gets separated due to the junction electric field (before they recombine) which produces an emf.

Reason: It is easier to observe the change in the current, with change in light intensity, if a reverse bias is applied.
Alternate Answer
The fractional change in the minority carrier current, obtained under reverse bias, is much more than the corresponding fractional change in majority carrier current obtained under forward bias.

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