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प्रश्न
The current in the forward bias is known to be more (~mA) than the current in the reverse bias (~μA). What is the reason, then, to operate the photodiode in reverse bias?
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उत्तर
The photodiode always work under reverse biasing conditions although the current produced is less. This is because in reverse bias, the width of the depletion layer increases which reduces the capacitance across the junction, thereby increasing response time. The sensitivity of a photodiode is thus very high, a property that is certainly desired.
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संबंधित प्रश्न
How is a Zener diode fabricated?
With what considerations in view, a photodiode is fabricated? State its working with the help of a suitable diagram.
Even though 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?
Why is zener diode fabricated by heavily doping both p- and n-sides of the junction?
Draw V − I characteristics of a p-n junction diode. Answer the following questions, giving reasons:
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(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 the circuit diagram of an illuminated photodiode and its I-V characteristics.
How can a photodiode be used to measure light intensity?
