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प्रश्न
With the help of a neat circuit diagram, explain the working of a photodiode.
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उत्तर
a. A photodiode is a special purpose P-N junction diode fabricated with a transparent window to allow light to fall on the diode.
b. When the photodiode is illuminated with light (photons) with energy h greater than the energy gap Eg of the semiconductor, then electron-hole pairs are generated due to the absorption of photons.
c. The diode is fabricated such that the generation of electron-hole pairs takes place in or near the depletion region of the diode.
d. Due to electric field of the junction, electrons and holes are separated before they recombine.
e. The direction of the electric field is such that electrons reach N-side and holes reach Pside. Electrons are collected on N-side and holes are collected on P-side giving rise to an e.m.f.
f. When an external load is connected, current flows. The magnitude of the photocurrent depends on the intensity of incident light.
g. It is easier to observe the change in the current with change in the light intensity, if a reverse bias is applied. Thus, photodiode can be used as a photodetector to detect optical signals.
संबंधित प्रश्न
How is a Zener diode fabricated?
Explain with the help of a diagram, how depletion region and potential barrier are formed in a junction diode.
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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?
Using the necessary circuit diagrams, show how the V-I characteristics of a p-n junction are obtained in
Forward biasing
How are these characteristics made use of in rectification?
Using the necessary circuit diagrams, show how the V-I characteristics of a p-n junction are obtained in
Reverse biasing
How are these characteristics made use of in rectification?
Carbon, silicon and germanium have four valence electrons each. These are characterised by valence and conduction bands separated by energy band gap respectively equal to (Eg)C, (Eg)Si and (Eg)Ge. Which of the following statements is true?
A p-n photodiode is fabricated from a semiconductor with band gap of 2.8 eV. Can it detect a wavelength of 6000 nm?
The width of depletion region of p-n junction diode is _______.
(A) 0.5 nm to 1 nm
(B) 5 nm to 10 nm
(C) 50 nm to 500 nm
(D) 500 nm to 1000 nm
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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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Explain its working and show the output, input waveforms.
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Explain how a potential barrier is developed in a p-n junction diode.
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Draw solar cell V-I characteristics.
With reference to Semiconductor Physics,
Name the process that causes depletion region in a p-n junction.
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In Figure, assuming the diodes to be ideal ______.
Read the following paragraph and answer the questions.
|
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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- 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
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Draw solar cells of I-V characteristics.
Draw the circuit diagram of an illuminated photodiode and its I-V characteristics.
How can a photodiode be used to measure light intensity?
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Identify the special purpose diodes 'A', 'B' and 'C' from the given symbols.
Select the wrong statement in the case of LED.
Consider the following statements A and B and identify the correct answer:
- For a solar-cell the I-V characteristics lies in the (IV) quadrant of the given graph.
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