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प्रश्न
Describe, with the help of a circuit diagram, the working of a photodiode.
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उत्तर
Photo diode is a p-n junction diode made of photosensitive semiconductor in which current carriers are generated by photons through photo excitation, i.e., photo conduction by light. It is operated under reverse bias below the breakdown voltage.
Working of Photo diode
- The diode is fabricated such that the generation of e-h pairs takes place in or near the depletion region of the diode.
When visible light of energy greater than forbidden energy gap ( \[h\nu > E_g\] ) is incident on a reverse bias p-n junction photo diode, additional electron-hole pairs are created in the depletion region ( or near the Junction).
- These charge carriers will be separated by the junction and made to flow across the junction, creating a reverse current across the junction.
- The direction of the electric field is such that electrons reach n-side and holes are
- The value of reverse saturation current increases with the increase in the intensity of incident light as shown here. Hence, thereverse saturation current through the photo diode varies linearly with the light intensity.
- collected on p-side giving rise to an emf.
I – V characteristics of photo diode
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संबंधित प्रश्न
If a small voltage is applied to a p-n junction diode, how will the barrier potential be affected when it is(ii) reveres biased?
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A p-n photodiode is fabricated from a semiconductor with band gap of 2.8 eV. Can it detect a wavelength of 6000 nm?
Draw V − I characteristics of a p-n junction diode. Answer the following questions, giving reasons:
(i) Why is the current under reverse bias almost independent of the applied potential up to a critical voltage?
(ii) Why does the reverse current show a sudden increase at the critical voltage?
Name any semiconductor device which operates under the reverse bias in the breakdown region.
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Read the following paragraph and answer the questions.
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LED is a heavily doped P-N junction which under forward bias emits spontaneous radiation. When it is forward-biased, due to recombination of holes and electrons at the junction, energy is released in the form of photons. In the case of Si and Ge diode, the energy released in recombination lies in the infrared region. LEDs that can emit red, yellow, orange, green and blue light are commercially available. The semiconductor used for fabrication of visible LEDs must at least have a band gap of 1.8 eV. The compound semiconductor Gallium Arsenide – Phosphide is used for making LEDs of different colours.
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- Why are LEDs made of compound semiconductor and not of elemental semiconductors?
- What should be the order of bandgap of an LED, if it is required to emit light in the visible range?
- A student connects the blue coloured LED as shown in the figure. The LED did not glow when switch S is closed. Explain why?
OR
iii. Draw V-I characteristic of a p-n junction diode in
(i) forward bias and (ii) reverse bias
Draw solar cells of I-V characteristics.
How can a photodiode be used to measure light intensity?
