CBSE Class 12-science Answered
why a photodiode is usally operated at a reverse bias
Asked by sasthasatlitec | 23 Oct, 2018, 10:35: PM
Expert Answer
when the photodiode or any diode is forward biased, electrons from the conduction band of semiconductors
recombine with holes from the valance band of semiconductors. If we consider diode as switch,
switch is on to conduct current when the diode is forward biased.
Photo diode is like an light operated switch. Hence instead of forward bias, photo diode is reverse biased to make the swith off.
When light is incident on photo diode, photo diode converts incident light to electric current and works like as if it is switched on.
The conversion of light energy to current is more efficient when reversed bias is applied across photo diode.
When absorbed photon generates electron-hole pairs, only those electron-hole pairs generated in depletion region
have a chance to contribute electric current. In reverse biased p-n junction, width of depletion region increases
as the applied reverse bias voltage across diode is increased (proportional to square root of voltage).
Hence by applying large voltage( but not large enough to increase leakage current) more of the incident photons are
converted to electric current or the efficiency increases.
Answered by Thiyagarajan K | 24 Oct, 2018, 01:36: AM
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