Photodiode MCQ

A photodiode is a PN-junction diode that uses light energy to generate an electric current. A photo-detector, also called a light detector or a photo-sensor, is a light-detecting device. In a reverse bias condition, photodiodes are designed to work. Photodiode materials include silicon, germanium, and indium gallium arsenide.

A photodiode emits photons in the form of light, which affect the formation of electron-hole pairs. If the energy of the falling photons (hν) is greater than the energy gap (E_g) of the semiconductor material, electron-hole pairs develop in the depletion zone of the diode. The produced electron-hole pairs are separated from one another before recombining due to the electric field of the junction.

The direction of the electric field forces electrons to migrate to the n-side of the diode, while the direction of the electric field forces holes to migrate to the p-side. When the number of electrons on the n-side and holes on the p-side rises, the electromotive force increases. The current flow through an external load is now visible when it is connected to the system.

Q1. According to the quantum theory, light consists of small energy packets known as

1. Proton

2. Photon

3. krypton

4. All are correct

Answer- 2) Photon

Light energy is carried in discrete units called photons, according to the quantum theory of light.

Q2. The active diameter of the photodiode is equal to  __________mm.

1. 150

2. 50

3. 25

4. 5

Answer- 3)  25

Q3. The photodiode can turn its current ON and OFF in about 

1. Milli seconds

2. Nano seconds

3. Micro seconds

4. a & c are correct

Answer- 2) Nano seconds

In nanoseconds, the photodiode may toggle its current ON and OFF. As a result, it is one of the most rapid photo detection devices available.

Q4. Photodiode is used to detect

1. Visible light

2. Invisible light

3. No light

4. Both visible and invisible light

Answer: 2) Both visible and invisible light

Q5. When a photodiode is used as a photodetector, it is always reverse biassed

1. When compared to the reverse biassed scenario, the power usage is significantly lower.

2. Incident photons form electron-hole pairs only when the photodiode is reverse biassed.

3. Light fluctuations can only be translated into current variations if the diode is reverse biassed.

4. The fractional change in the reverse current when photons strike the diode is substantially bigger than the fractional change in the forward current.

Answer: 4) The fractional change in the reverse current when photons strike the diode is substantially bigger than the fractional change in the forward current.

When the photodiode is forward biassed and light strikes it, the current created by the voltage exceeds the number the current produced by the light. When light falls on a diode that is reverse biassed, the current changes by a similar amount.

Q6. The greatest wavelength of photons that a photodiode built of a semiconductor with a bandgap of 2eV can detect is around

1. 620 nm

2. 700 nm

3. 740 nm

4. 1240 nm

Answer: 1) 620 nm

The wavelength of the photon is given as:

λE = 12400 

Hence, λ = 12400/E

[Remember that a photon with an energy of 1eV has a wavelength of 12400A˚, and that energy is inversely proportional to wavelength.].

AS, E = 2eV we have

 λ = 12400/2 = 6200A˚ = 620nm 

Photons with a wavelength higher than 640 nm have less energy than photons with a wavelength less than 2eV, hence they cannot create electron-hole pairs in a semiconductor with a band gap of 2eV.

Q7. When there is no incident light, the reverse current in a photodiode is essentially non-existent and is referred to as

1. Zener current

2. Dark current

3. Photocurrent

4. PIN current

Answer: 2) Dark current

When there is no incident light, the reverse current, also known as the dark current, is almost non-existent. When the amount of light intensity is increased, the reverse current increases as well.

Q8. The recombination of free electrons and holes in a forward biassed diode produces

1. Heat

2. Light

3. Radiation

4. All the above

Answer: 4) All the above

Due to the temperature effect, recombination between holes and electrons occurs when the diodes are forward biassed, resulting in heat, light, and radiation.

Q9. The depletion region’s width is

1. Directly proportional to the doping

2. inversely proportional to the doping

3. Independent of doping

4. None of the above

Answer: 2) inversely proportional to the doping

Q10. Which of the following structures is more complex than the p-i-n photodiode?
a) Avalanche photodiode
b) p-n junction diode
c) Zener diode
d) Varactor diode

Answer: 1) Avalanche photodiode
In optical communications, the avalanche photodiode is the second most common form of detector. This diode is more advanced, resulting in a significantly larger electric field zone.

Q11. The phenomenon leading to avalanche breakdown in reverse-biassed diodes is called
a) Auger recombination
b) Mode hopping
c) Impact ionisation
d) Extract ionisation

Answer: 3) Impact ionisation
Almost all photons are absorbed and carrier pairs are formed in the depletion area. As a result, a high-field zone emerges, where carriers gain energy in order to excite new carrier pairs. This is a process known as impact ionisation.

Q12. The LED emits light when it is
a) reverse biassed
b) unbiassed
c) forward biassed
d) none of these

Ans: 3) forward biassed

A light emitting diode (LED) is a light-emitting device. When the LED is forward biassed, it produces light; when it is reverse biassed, it produces no light. The square of the current flowing through the gadget determines the intensity of light.

Q13. The LED works on the principle of
a) fluorescence
b) hall effect
c) electroluminescence
d) none of these

Ans: 3) electroluminescence

A light-emitting diode (LED) produces light when current travels through it. Electrons recombine with electron holes in the semiconductor, producing energy in the form of photons.

Q14. The photodiode current under no light is known as
a) forward current
b) maximum current
c) dark current
d) none of these

Ans: 3) dark current

Dark current is the current that exists in a photodiode’s circuit even when no visible light is falling on it.

Q15. Photo current is directly proportional to
a) forward current
b) reverse current
c) intensity of light
d) none of these

Ans: 3) intensity of light

The number of photoelectrons emitted per second is directly proportional to the intensity of incident radiations, therefore the number of photoelectrons emitted per second is directly proportional to the intensity of incident radiations.

Q16. The unit of intensity of light is
a) Lm/A
b) Lm/W
c) Lm/w²
d) Lm/m²

Ans: 4) Lm/m²

Light intensity is measured in lumens per square metre or lux, while light output is measured in lumens.

Q17. The photodiode characteristics lies in the
a) first quadrant
b) second quadrant
c) third quadrant
d) fourth quadrant

Ans: 3) third quadrant