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  • State the reason, why the photodiode is always operated under reverse bias. Write the working principle of operation of a photodiode. The semiconducting material used to fabricate a photodiode has an energy gap of 1.2eV. Using calculations, show whethe

State the reason, why the photodiode is always operated under reverse bias. Write the working principle of operation of a photodiode. The semiconducting material used to fabricate a photodiode has an energy gap of 1.2eV. Using calculations, show whether it can detect light of wavelength of 400 nm incident on it.

 

 
 
 
 
 

Answers (1)

photodiode converts incident light to electric current more effectively at reverse bias.
when the photodiode is illuminated with the photon of energy greater than the energy of semiconductor, electron-hole pairs are generated due to absorption if photon. e-h pair generation takes place near the depletion region. Due to the electric field of the junction electrons and holes are separated before recombination.
The electrons are collected on n side and holes on giving rise to an emf. Now when an external load connected, current flows.
given energy gap = 1.2 e V
E= \frac{hc}{\lambda }= \frac{6\cdot 63\times 10^{-34}\times 3\times 10^{8}}{400\times 10^{-19}}
                 = 4\cdot 9725\times 10^{-19}
                 = \frac{4\cdot 9725eV}{1\cdot 6}= 2\cdot 94eV
 E> E_{g}
Therefore 400 nm can be detected 

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Safeer PP

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