# Electronic Devices and Circuits Questions and Answers – Electrons and Holes in Semiconductor

This set of Electronic Devices and Circuits Multiple Choice Questions & Answers (MCQs) focuses on “Electrons and Holes in Semiconductor”.

1. Which of the following expressions represents the correct distribution of the electrons in the conduction band? (gc(E)=density of quantum states, fF(E)=Fermi dirac probability
a) n(E)=gc(E)*fF(E)
b) n(E)=gc(-E)*fF(E)
c) n(E)=gc(E)*fF(-E)
d) n(E)= gc(-E)*fF(-E)

Explanation: The distribution of the electrons in the conduction band is given by the product of the density into Fermi-dirac distribution.

2. What is the value of the effective density of states function in the conduction band at 300k?
a) 3*1019 cm-3
b) 0.4*10-19 cm-3
c) 2.5*1019 cm-3
d) 2.5*10-19 cm-3

Explanation:
Substituting the values of mn=m0 ,h=6.626*10-34J/s ,k=1.38*10-23 and T=300K, we get
Nc=2.5*1019 cm-3.

3. In a semiconductor which of the following carries can contribute to the current?
a) Electrons
b) Holes
c) Both
d) None

Explanation: In a semiconductor, two types of charges are there by which the flow of the current takes place. So, both the holes and electrons take part in the flow of the current.

4. Which of the following expressions represent the Fermi probability function?
a) fF(E)=exp(-[E-EF]/KT)
b) fF(E)=exp(-[EF-E]/KT)
c) fF(E)=exp([E-EF]/KT)
d) fF(E)=exp(-[EF-E]/KT)

Explanation: It is the correct formula for the Fermi probability function.

5. Electrons from valence band rises to conduction band when the temperature is greater than 0 k. Is it True or False?
a) True
b) False

Explanation: As the temperature rises above 0 k, the electrons gain energy and rises to the conduction band from the valence band.
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6. What is the intrinsic electrons concentration at T=300K in Silicon?
a) 1.5*1010cm-3
b) 1.5*10-10cm-3
c) 2.5*1019cm-3
d) 2.5*10-19cm-3

Explanation: Using the formula,

We get, ni=1.5*1010cm-3.

7. The intrinsic Fermi level of a semiconductor depends on which of the following things?
a) Emidgap
b) mp*
c) mn*
d) All of the mentioned

Explanation:
From the above formula, Efidepends on all of the options given.

8. What is the difference between the practical value and theoretical value of ni?
a) Factor of 1
b) Factor of 2
c) Factor of 3
d) Factor of 4

Explanation: This is practically proved.

9. The thermal equilibrium concentration of the electrons in the conduction band and the holes in the valence band depends upon?
a) Effective density of states
b) Fermi energy level
c) Both A and B
d) Neither A nor B

Explanation: The electrons and holes depends upon the effective density of the states and the Fermi energy level given by the formula,
.

10. In which of the following semiconductor, the concentration of the holes and electrons is equal?
a) Intrinsic
b) Extrinsic
c) Compound
d) Elemental

Explanation: In the intrinsic semiconductor, ni=pi that is the number of the electrons is equal to the number of the holes. Whereas in the extrinsic conductor ni is not equal to pi.

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