Dharani Vidhya manthir senior secondary school

Mannargudi

CH-14 SEMICONDUCTOR MCQ

Class 12 - Physics
Time Allowed: 1 hour Maximum Marks: 75

1. The relation between the forward current If and saturation current Is for p-n junction diode is: [1]

a) If Is = 1 b) If = Is

c) If = Is [
qV
− 1] d) If = Is e
(qV /KT )−1

KT

2. A semiconductor is damaged by a strong current, because of [1]

a) excess of electrons b) lack of free electrons

c) none of these d) decrease in electrons

3. Number of atoms per unit cell in bcc lattice is [1]

a) 9 b) 2

c) 4 d) 1
4. In p-type semiconductor, [1]
A. major current carrier are electrons
B. major carrier are mobile negative ions
C. major carrier are mobile holes
D. the number of mobile holes exceeds the number of acceptor atoms

a) Option C b) Option A

c) Option D d) Option B
5. In an unbiased p-n junction, [1]

a) undetermined b) high potential at n side and low potential at

p side

c) p and n both are at same potential d) high potential at p side and low potential at
n side
6. The peak voltage in the output of a half wave diode rectifier fed with a sinusoidal signal without filter is 10 V. [1]
The d.c. component of the output voltage is:

a) 10 V b) 10/π Volts
–
c) 10/√2 Volts d) 20/π Volts
7. In the middle of the depletion layer of reverse biased p-n junction, the: [1]

a) potential is maximum b) potential is zero

c) electric field is zero d) electric field is maximum

8. Hole is [1]

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 a) Gap between valence band and conduction b) Particle similar to that of electron
band

c) A vacancy created when an electron leaves a d) An anti-particle of electron.

covalent bond.
9. In a middle of the depletion layer of a reverse biased p-n junction, the [1]

a) electric field is maximum b) potential is zero

c) potential is maximum d) electric field is zero

10. The state of energy gained by valence electrons when the temperature is raised or when an electric field is [1]
applied is called

a) valence band b) none of these

c) conduction band d) forbidden band

11. In the case of forward biasing of p-n junction, which one of the following figures correctly depicts the direction [1]
of flow of carriers?

a) b)

c) d)

12. A half wave rectifier is being used to rectify an alternating voltage of frequency 50 Hz. The number of pulses of [1]
rectified current obtained in one second is

a) 50 Hz b) 200 Hz

c) 100 Hz d) 25 Hz
13. C and Si both have the same lattice structure, having 4 bonding electrons in each. However, C is an insulator [1]
whereas Si is an intrinsic semiconductor. This is because
A. In case of C the valence band is not completely filled at absolute zero temperature.
B. In case of C the conduction band is partly filled even at absolute zero temperature.
C. The four bonding electrons in the case of C lie in the second orbit, whereas in the case of Si they lie in the
third.
D. The four bonding electrons in the case of C lie in the third orbit, whereas for Si they lie in the fourth orbit.

a) Option B b) Option A

c) Option D d) Option C
14. Energy required to break one bond in DNA is approximately [1]

a) ≈ 2.1eV b) ≈ 1eV

c) ≈ 0.1eV d) ≈ 0.01eV
15. The manifestation of band structure in solids is due to: [1]

a) Boltzmann's law b) Pauli's exclusion principle

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 c) Bohr's correspondence principle d) Heisenberg's uncertainly principle
16. In an unbiased p-n junction, holes diffuse from the p-region to n-region because: [1]

a) all of these b) they move across the junction by the

potential difference

c) hole concentration in p-region is more as d) free electrons in the n-region attract them
compared to n-region
17. Forward biasing of p-n junction offers [1]

a) zero resistance b) high resistance

c) infinite resistance d) low resistance

18. The barrier potential of a p-n junction diode does not depend on [1]

a) temperature b) forward bias

c) doping density d) diode design

19. The cations and anions are arranged in alternate form in [1]

a) ionic crystal b) semiconductor crystal

c) covalent crystal d) metallic crystal

20. The probability of finding an electron in Fermi energy level is: [1]

a) 50% b) 20%

c) 0% d) 100%
21. Diamond is very hard because [1]

a) high melting point b) it has large cohesive energy

c) it is covalent solid d) insoluble in all solvents

22. Suitable impurities are added to a semiconductor depending upon its use. This is done to [1]

a) increase its electrical resistivity b) enable it to withstand high voltage

c) increase its electrical conductivity d) increase its life

23. In forward bias, the width of a potential barrier in a p-n junction diode [1]

a) remains constant b) increases

c) decreases d) first remains constant then decreases

24. A Ge specimen is doped with Al. The concentration of acceptor atoms is ≈ 1021 atoms m-3. Given that the [1]

intrinsic concentration of electron-hole pair is ≈ 1019 m-3, the concentration of electrons in the specimen is

a) 1017 m-3 b) 102 m-3

c) 1015 m-3 d) 104 m-3

25. Pure Si at 500 K has equal number of electron (ne) and hole (nh) concentrations of 1.5 × 1016 m-3. Doping by [1]

indium increases nh to 4.5 × 1022 m-3. The doped semiconductor is of

a) n-type with electron concentration, ne = 5 × b) p-type with electron concentration, ne = 2.5

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 1022 m-3 × 1010 m-3

c) p-type having electron concentration, ne = 5 d) n-type with electron concentration, ne = 2.5

× 109 m-3 × 1023 m-3

26. To a germanium sample, traces of gallium are added as an impurity. The resultant sample would behave like [1]

a) an n-type semiconductor b) a p-type semiconductor

c) an insulator d) a conductor
27. If a small amount of antimony is added to germanium crystal [1]

a) it becomes a p-type semiconductor b) the antimony becomes an acceptor atom

c) its resistance is increased d) there will be more free electrons than holes
in the semiconductor
28. At which temperature, a pure semiconductor behaves slightly as a conductor? [1]

a) both low and room temp. b) room temp.

c) low temp. d) high temp.

o

29. Sodium has body-centered packing. If the distance between two nearest atoms is 3.7 A, then lattice parameter is [1]

o o
a) 3.3 A b) 3.9 A
o o
c) 4.8 A d) 4.3 A

30. In n-type semiconductor when all donor states are filled, then the net charge density in the donor states becomes: [1]

a) < 1, but not zero b) > 1

c) 1 d) zero
31. The depletion layer in the p-n junction is caused due to [1]

a) drift of electrons b) migration of impurity ions

c) diffusion of carrier ions d) drift of holes

32. In forward bias the width of depletion layer [1]

a) independent of V b) none of these

c) decreases with increase in V d) increases with increase in V

33. Carbon (C), silicon (Si) and germanium (Ge) have four valence electrons each. At room temperature, which one [1]
of the following statements is most appropriate?

a) The number of free conduction electrons is b) The number of free conduction electrons is
significant only in Si, but small in C. significant in C, but small in Si and Ge.

c) The number of free conduction electrons is d) The number of free conduction electrons is
significant in all the three. negligible in all the three.
34. What is the packing fraction of a bcc lattice? [1]

a) π√3
b) π√3

4 8

c) 2π√3
d) π√2

8 8

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35. Which of the following is the weakest kind of bonding in solids? [1]

a) Van der Waals b) Covalent

c) Metallic d) Ionic
o

36. Copper has face centered cubic (fcc) lattice with interatomic spacing equal to 2.54 A. The value of lattice [1]

constant for this lattice is

o o
a) 3.59 A b) 1.27 A
o o
c) 5.08 A d) 2.54 A

37. In an n-type semiconductor, the donor energy level lies [1]

a) in the conduction band b) just below the conduction band

c) just above the valance band d) at the center of the energy gap
38. When a p-n diode is reverse biased, then [1]

a) the height of the potential barrier is reduced b) the depletion region is increased

c) no current flows d) the depletion region is reduced

39. A bridge rectifier is shown in the figure. Alternating input is given across A and C. If the output is taken across [1]
BD, then it is:

a) full wave rectified b) zero

c) half wave rectified d) same as input

40. The valence electron in an alkali metal is a [1]

a) s-electron b) p-electron

c) d-electron d) f-electron
41. When we apply reverse bias to a junction diode it [1]

a) lowers the potential barrier b) raises the potential barrier

c) increases the minority carrier current d) increases the majority carrier current
42. In n-type semiconductor majority carriers and minority carriers are respectively [1]

a) germanium and silicon b) aluminum and boron

c) holes and electrons d) electrons and holes

43. The number of valence electrons in a good conductor is generally [1]

a) three or less than three b) four

c) six or more than six d) five

44. Atomic packing factor of simple cubic cell is [1]

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 a) b)
π π

6 8

c) π
d) π
√3

3√2 8

45. In the terminology related to semiconductors, what is a hole? [1]

a) space which was previously occupied by an b) space which is negatively charged

electron

c) dense area in space which even absorbs light d) a hole in space-time distribution of the
i.e., black hole. universe
46. The electrical conductivity of semiconductor increases when electromagnetic radiation of wavelength shorter [1]
than 2800 nm is incident on it. The band gap in (eV) for the semiconductor is:

a) 0.5 eV b) 0.7 eV

c) 2.5 eV d) 1.2 eV
47. At absolute zero temperature, a semiconductor acts as a/an [1]

a) conductor b) none of these

c) dielectric d) insulator
48. In semiconductors at the room temperature [1]

a) the valence band is partially empty and the b) the conduction band is completely empty
conduction band is partially filled

c) the valence band is completely filled and the d) the valence band is completely filled
conduction band is partially filled
49. Forbidden energy gap for a diamond is about: [1]

a) 1.5 eV b) 6 eV

c) 1 eV d) 0.6 eV
50. In a semiconductor the forbidden energy gap between the valence band and the conduction band is of the order [1]
of:

a) 5 eV b) 1 eV

c) 1 MeV d) 1 KeV
51. The conductivity of p-type semiconductor is due to [1]

a) positive ions b) negative ions

c) electrons d) holes
52. Drift current in a p-n junction is due to [1]

a) none of these b) electric field

c) collision of electrons d) charge carriers density

53. Current through the ideal diode is: [1]

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 a) 20 A b) ( 1

20
)A

c) zero d) ( 1

50
)A
54. In semiconducting materials, the mobilities of electrons and holes are μ and μ respect. Which of the following [1]
e h

is true?

a) μ e = μh b) μe > μh

c) μ e < 0; μh > 0 d) μe < μh

55. The behavior of Ge as a semiconductor is due to the width of [1]

a) forbidden band being small and narrow b) forbidden band being large and wide

c) conduction band being small and narrow d) conduction band being large
56. What accounts for the flow of charge carriers in forward and reverse biasing of silicon p-n diode? [1]

a) drift in reverse bias and diffusion in forward b) drift in forward bias and diffusion in reverse
bias bias

c) diffusion in both forward and reverse bias d) drift in both reverse and forward bias
57. A semiconductor has electron and hole mobilities μ and μ respectively. If its intrinsic carrier density is ni,
e h [1]

then what will be the value of hole concentration nh for which the conductivity will be minimum at a given
temperature?
−
μ
− −
μ
−
a) n e√
e
b) ne √
h

μh μe

−
μ
− −
μ
−
c) n i√
μh
e
d) ni √
h

μe

58. A donor impurity results in [1]

a) increase of resistance of the semiconductor b) production of n-semiconductor

c) energy bands just above the filled valency d) production of p-semiconductor

59. In the half-wave rectifier circuit operating from 50 Hz main frequency, the fundamental frequency in the ripple [1]
would be

a) 70.7 Hz b) 50 Hz

c) 100 Hz d) 25 Hz
60. A p-n junction diode is connected to a battery of emf 5.5 V and external resistance 5.1 kΩ . The barrier potential [1]
in the diode is 0.4 V. The current in the circuit is:

a) 1 mA b) 1.08 mA

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 c) 0.08 mA d) 1 A
61. The typical ionization energy of a donor in silicon is [1]

a) 1.0 eV b) 10.0 eV

c) 0.001 eV d) 0.1 eV
62. Assertion (A): If the temperature of a semiconductor is increased then its resistance decreases. [1]
Reason (R): The energy gap between conduction band and valence band is very small.

a) Both A and R are true and R is the correct b) Both A and R are true but R is not the
explanation of A. correct explanation of A.

c) A is true but R is false. d) A is false but R is true.

63. Assertion (A): Electron has higher mobility than hole in a semiconductor. [1]
Reason (R): The mass of electron is less than the mass of the hole.

a) Both A and R are true and R is the correct b) Both A and R are true but R is not the
explanation of A. correct explanation of A.

c) A is true but R is false. d) A is false but R is true.

64. Assertion (A): The diffusion current in a p-n junction is from the p-side to the n-side. [1]
Reason (R): The diffusion current in a p-n junction is greater than the drift current when the junction is in
forward biased.

a) Both A and R are true and R is the correct b) Both A and R are true but R is not the
explanation of A. correct explanation of A.

c) A is true but R is false. d) A is false but R is true.

65. Assertion (A): In semiconductors, thermal collisions are responsible for taking a valence electron to the [1]
conduction band.
Reason (R): The number of conduction electrons goes on increasing with time as thermal collisions
continuously take place.

a) Both A and R are true and R is the correct b) Both A and R are true but R is not the
explanation of A. correct explanation of A.

c) A is true but R is false. d) A is false but R is true.

66. Assertion (A): The number of electrons in a p-type silicon semiconductor is less than the number of electrons in [1]
a pure silicon semiconductor at room temperature.
Reason (R): It is due to law of mass action.

a) Both A and R are true and R is the correct b) Both A and R are true but R is not the
explanation of A. correct explanation of A.

c) A is true but R is false. d) A is false but R is true.

67. Assertion (A): When two semiconductor of p and n-type are brought in contact, they form p-n junction which [1]
act like a rectifier.
Reason (R): A rectifier is used to convert alternating current into direct current.

a) Both A and R are true and R is the correct b) Both A and R are true but R is not the
explanation of A. correct explanation of A.

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 c) A is true but R is false. d) A is false but R is true.
68. Assertion (A): A pure semiconductor has a negative temperature coefficient of resistance. [1]
Reason (R): In a semiconductor on raising the temperature, more charge carriers are released, conductance
increases and resistance decreases.

a) Both A and R are true and R is the correct b) Both A and R are true but R is not the
explanation of A. correct explanation of A.

c) A is true but R is false. d) A is false but R is true.

69. Assertion (A): The drift current in a p-n junction is from the n-side to the p-side. [1]
Reason (R): It is due to free electrons only.

a) Both A and R are true and R is the correct b) Both A and R are true but R is not the
explanation of A. correct explanation of A.

c) A is true but R is false. d) A is false but R is true.

70. Assertion (A): A p-n junction with reverse bias can be used as a photo-diode to measure light intensity. [1]
Reason (R): In a reverse bias condition the current is small but it is more sensitive to changes in incident light
intensity.

a) Both A and R are true and R is the correct b) Both A and R are true but R is not the
explanation of A. correct explanation of A.

c) A is true but R is false. d) A is false but R is true.

71. Assertion (A): Gallium arsenide phosphide is used for making LEDs. [1]
Reason (R): Valence and conduction bands overlap in case of semiconductors.

a) Both A and R are true and R is the correct b) Both A and R are true but R is not the
explanation of A. correct explanation of A.

c) A is true but R is false. d) A is false but R is true.

72. Assertion (A): A pure semiconductor has a negative temperature coefficient of resistance. [1]
Reason (R): On raising the temperature, more charge carriers are released, conductance increases and resistance
decreases.

a) Both A and R are true and R is the correct b) Both A and R are true but R is not the
explanation of A. correct explanation of A.

c) A is true but R is false. d) A is false but R is true.

73. Assertion (A): The resistivity of a semi|conductor increases with temperature. [1]
Reason (R): The atoms of a semiconductor vibrate with larger amplitudes at higher temperatures thereby
increasing its resistivity.

a) Both A and R are true and R is the correct b) Both A and R are true but R is not the
explanation of A. correct explanation of A.

c) A is true but R is false. d) A is false but R is true.

74. Assertion (A): Silicon is preferred over germanium for making semiconductor devices. [1]
Reason (R): The energy gap in germanium is more than the energy gap in silicon.

a) Both A and R are true and R is the correct b) Both A and R are true but R is not the

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 explanation of A. correct explanation of A.

c) A is true but R is false. d) A is false but R is true.

75. Assertion (A): At a fixed temperature, silicon will have a minimum conductivity when it has a smaller acceptor [1]
doping.
Reason (R): The conductivity of an intrinsic semiconductor is slightly higher than that of a lightly doped p-type.

a) Both A and R are true and R is the correct b) Both A and R are true but R is not the
explanation of A. correct explanation of A.

c) A is true but R is false. d) A is false but R is true.

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