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Test: Intrinsic Semiconductors - Electronics and Communication Engineering (ECE) MCQ


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10 Questions MCQ Test - Test: Intrinsic Semiconductors

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Test: Intrinsic Semiconductors - Question 1

If Ie and Ih are the electron and the hole current respectively for the intrinsic semiconductor, then the total current is equal to the:

Detailed Solution for Test: Intrinsic Semiconductors - Question 1
  • We know that in a semiconductor the total current is the sum of the electron current and the hole current.
  • Therefore if the Ie and Ih are the electrons and the hole current respectively for the intrinsic semiconductor, then the total current is given as,
    • ⇒ I = Ie + Ih

Hence, option 3 is correct.

Test: Intrinsic Semiconductors - Question 2

The mobility of holes is ______ mobility of electrons in intrinsic semiconductors.

Detailed Solution for Test: Intrinsic Semiconductors - Question 2

Semiconductor: 

  • Semiconductors are materials that have a conductivity between conductors and insulators.
    • Semiconductors are made of compounds such as gallium arsenide or pure elements, such as germanium or silicon.
  • Holes and electrons are the types of charge carriers accountable for the flow of current in semiconductors. 
    • ​Holes (valence electrons) are the positively charged electric charge carrier whereas electrons are the negatively charged particles.
  • Intrinsic semiconductors are made of pure elements.
  • The mobility of electrons and holes depends on their effective masses. The effective mass of electrons is less than that of holes hence electrons have higher mobility than holes.

Hence, option 3 is correct.

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Test: Intrinsic Semiconductors - Question 3

An intrinsic semiconductor behaves as an insulator at

Detailed Solution for Test: Intrinsic Semiconductors - Question 3
  • In an intrinsic semiconductor, conduction occurs only when the electrons in the valence band can move to the conduction band.
  • To cross over the energy gap between the valence band and conduction band, the electrons will require some amount of energy.
  • Hence, at higher temperatures, the electrons will gain energy and jump into the conduction band.
  • 0 K is also known as absolute zero. It is the temperature at which the particles in a substance are motionless.
  • At 0 K, the electrons will not have the energy to move into the conduction band.
  • Thus, there is no conductivity at 0 K in intrinsic semiconductors and it behaves as an insulator.
Test: Intrinsic Semiconductors - Question 4

Which of the following 14th group element is not a semiconductor?

Detailed Solution for Test: Intrinsic Semiconductors - Question 4
  • When the external voltage becomes greater than the value of the potential barrier for the diode the potential barriers opposition will be overcome and the current will start to flow. This is the conventional current.
  • The potential barrier is approx 0.3 volts for germanium and 0.7 volts for silicon while for the carbon it is 7eV.
  • This is far much higher for Carbon to make it a semiconductor that has lower forbidden energy gaps (Si and Ge).
  • This is why Carbon is not a semiconductor.

So the correct answer is option 3.

Test: Intrinsic Semiconductors - Question 5

Which of following is the majority charge carrier particle in type N-type extrinsic semiconductor?

Detailed Solution for Test: Intrinsic Semiconductors - Question 5
  • In n-type semiconductors, electrons are the majority carriers and holes are the minority carriers. 
    • A common dopant for n-type silicon is phosphorus or arsenic.

The correct option is 1.

Test: Intrinsic Semiconductors - Question 6

Which type of behaviour is shown by a pure Germanium at absolute zero temperature?

Detailed Solution for Test: Intrinsic Semiconductors - Question 6
  • An ideal, perfectly pure semiconductor (with no impurities) is called an intrinsic semiconductor.
  • At absolute zero temperature valence band is full of electrons and the conduction band is empty, hence there are no free electrons in the conduction band and holes in the valence band.
  • The charge carrier concentration is zero. Hence intrinsic semiconductor behaves like an insulator

Hence, at zero temperature the intrinsic semiconductor behaves like an insulator. The correct option is 3.

Test: Intrinsic Semiconductors - Question 7

When the electrical conductivity of a semiconductor is due to the breaking of its covalent bonds, then the semiconductor is said to be :

Detailed Solution for Test: Intrinsic Semiconductors - Question 7
  • An intrinsic semiconductor is made up of only a single type of element.
  • Germanium (Ge) and Silicon (Si) are the most common type of intrinsic semiconductor.
  • When the temperature rises, due to collisions, some covalent bonds break and few electrons are unbounded and become free to move through the lattice, thus creating an absence in its original position (hole).​ Hence, option 3 is correct.
Test: Intrinsic Semiconductors - Question 8

What is the difference between intrinsic semiconductor and extrinsic semiconductor?

Detailed Solution for Test: Intrinsic Semiconductors - Question 8
  • Option 1: The conductivity of an intrinsic semiconductor is very low at room temperature. It means very low or no current flows at room temperature.
    • So this is an incorrect statement.
  • Option 2: Since intrinsic semiconductors are pure semiconductors they have the same number of holes and electrons. 
  • Option 3 and 4: The intrinsic semiconductor is a pure semiconductor and an extrinsic semiconductor is a semiconductor with impurity.
    • So option 4 gives the correct statement.

So the correct answer is option 4.

Test: Intrinsic Semiconductors - Question 9

Which of the following is responsible for conductivity in intrinsic semiconductor

Detailed Solution for Test: Intrinsic Semiconductors - Question 9
  • In an intrinsic semiconductor, the number of electrons is equal to the number of holes. Hence at room temperature, no free electron is available for conduction
  • If some energy is applied to the atoms of intrinsic semiconductor the covalent bonds will break and electrons will be free 
  • Each electron will leave behind a hole and the process will continue, and charge flows through the intrinsic semiconductor

Therefore intrinsic semiconductor conductivity is due to breaking off the covalent bond. Hence option (4) is correct

Test: Intrinsic Semiconductors - Question 10

In intrinsic semiconductor at room temperature, the number of electrons and holes are:

Detailed Solution for Test: Intrinsic Semiconductors - Question 10
  • Intrinsic semiconductors are made of pure elements.
  • Since no impurity is mixed in the intrinsic semiconductors, so the numbers of electrons and holes remain equal in an intrinsic semiconductor.

Hence, option 1 is correct.

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