Physics

Semiconductors and Diodes

461 Questions

Semiconductors and diodes form the foundation of modern electronics, covering topics like intrinsic carrier concentration and Zener breakdown. Questions often explore the characteristics of bipolar junction transistors (BJT) and the properties of doped silicon materials. This topic is crucial for physics and electronics engineering competitive exams.

Zener diode breakdownBJT circuit analysisIntrinsic carrier concentrationDoping in semiconductorsEmitter follower circuit

Semiconductors and Diodes Questions

Multiple choice zener diode special purpose diodes electronic devices semiconductor electronics: materials, devices and simple circuits physics

A Zener diode

  1. is a lightly doped junction diode.

  2. heavily doped junction diode.

  3. is either p-type or n-type.

  4. has no p-n junction.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The reverse breakdown voltage depends on doping of the diode. Hence, in the Zener diode the heavy doping of its p-n junction is done. The depletion region formed in the diode is very thin ($<1\ m$) and the reverse bias voltage of about $5\ V$ which is less than ordinary diode.

Multiple choice zener diode special purpose diodes electronic devices semiconductor electronics: materials, devices and simple circuits physics

The current flow in a Zener diode is mainly due to

  1. thermally generated charge carriers

  2. minority charge carriers

  3. collision generated charge carriers

  4. ions
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

When the reverse bias breakdown voltage is exceeded, a conventional diode is subject to high current due to avalanche breakdown. Avalanche breakdown occurs in reverse bias when the applied voltage is high enough, the free electron may move fast enough to knock other electrons free, creating more free-electron-hole pairs (i.e., more charge carriers), increasing the current. Thus, the current flow in a Zener diode is mainly due to collision generated charge carriers

Multiple choice zener diode special purpose diodes electronic devices semiconductor electronics: materials, devices and simple circuits physics

At breakdown voltage, the rate of creation of hole-electron pairs is _____  leading to the _______  in current. 

  1. increased, decrease

  2. increased, increase

  3. decreased, increase

  4. decreased, decrease
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

When the reverse voltage across a diode is very large, the valance electrons become free due to applied high electric field and get enough acceleration to make other electrons free, thus create a lot of electron-hole pairs in a short time. As the number of charge carriers increases, current also increases.

Therefore, at breakdown voltage, the rate of creation of hole-electron pairs is increased leading to the increase in current.

Multiple choice zener diode special purpose diodes electronic devices semiconductor electronics: materials, devices and simple circuits physics

Which of these is the best description of a Zener diode ?

  1. It is a constant voltage device.

  2. It operates in the reverse region.

  3. It is a constant current device.

  4. It works in forward region.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Zener diode is a p-n junction diode working in the breakdown region. It is used as a voltage regulator/stabilizer to provide a constant voltage from a source whose voltage may fluctuate over a wide range.

Multiple choice zener diode special purpose diodes electronic devices semiconductor electronics: materials, devices and simple circuits physics

Zener-diode is used in.

  1. Amplification

  2. Rectification

  3. Oscillator in producing oscillations

  4. Volatge regulation
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

 A voltage regulator circuit can be designed using a zener diode to maintain a constant DC output voltage across the load in spite of variations in the input voltage or changes in the load current. 

Multiple choice zener diode special purpose diodes electronic devices semiconductor electronics: materials, devices and simple circuits physics

Zener diodes with breakdown voltage ranging over 2V- 200 V are commercially available. Breakdown voltage of a zener diode

  1. Increases with increasing doping concentration

  2. Decreases with increasing doping concentration

  3. Does not depend on doping concentration

  4. May increases or decreases with increasing doping concentration
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

For Zener Diodes, the breakdown voltage decreases with increasing doping concentration.

Multiple choice zener diode special purpose diodes electronic devices semiconductor electronics: materials, devices and simple circuits physics

In a zener diode, break down occurs in reverse bias due to

  1. Impact ionisation

  2. Internal field emission

  3. High doping concentration

  4. All of these
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Zener breakdown occurs due to high electric fields (internal field emission) in heavily doped diodes, while avalanche breakdown occurs due to impact ionization. Both are mechanisms associated with reverse bias breakdown.

Multiple choice zener diode special purpose diodes electronic devices semiconductor electronics: materials, devices and simple circuits physics

Which of the following is/are true regarding  breakdown voltage of Zener diode?

  1. If the reverse bias voltage across a p-n junction diode is increased, at a particular voltage the reverse current suddenly decreases to a large value

  2. The holes in the n-side and the conduction electrons in the p-side are accelerated due to the reverse bias voltage.

  3. The voltage at which the rate of creation of hole-electron pairs is increased leading to the increased current is called avalanche breakdown

  4. None of the above
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Consider applying an external voltage to the junction with the the negative terminal connected to the P type material and the positive terminal connected to the N type material. For the P-N junction this would require injecting electrons into the P type material. These electrons would recombine with holes and therefore further deplete the majority charge carriers in the P type semiconductor. 


Also removing electrons from the N type material would obviously cause further depletion the free electrons (the majority charge carriers in the N type semiconductor). This causes a widening of the depletion layer and an increase in the charge at the junction which reinforces the barrier voltage to oppose the applied voltage. The net result is that when the P-N junction is reversed biased it blocks current flow.

Multiple choice zener diode special purpose diodes electronic devices semiconductor electronics: materials, devices and simple circuits physics

Which of the following semi-conducting devices is used as voltage regulator?

  1. Zener diode

  2. LASER diode

  3. Photo diode

  4. Solar cell
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Zener diode is used as a voltage regulator device because the voltage across the zener diode in reverse bias is constant after reaching certain value i.e. breakdown voltage.

Multiple choice zener diode special purpose diodes electronic devices semiconductor electronics: materials, devices and simple circuits physics

What is true about the breakdown voltage in a zener diode?

  1. It decreases when current increases.

  2. It destroys the diode.

  3. It equals the current times the resistance.

  4. It is approximately constant.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

As the current in the zener diode increases, the voltage across the diode remains constant. This voltage will be equal to the zener breakdown voltage