Electronics Device and Circuits – Semiconductor Physics MCQs

In this section of Electronic Devices and Circuits.It contain Semiconductor Physics / Semiconductor Fundamentals MCQs (Multiple Choice Questions Answers).All the MCQs (Multiple Choice Question Answers) requires in depth reading of Electronic Devices and Circuits Subject as the hardness level of MCQs have been kept to advance level.These Sets of Questions are very helpful in Preparing for various Competitive Exams and University level Exams.

This Section covers below lists of topics :

Bohr’s Atomic structure MCQs.
Energy levels ,Energy bands MCQs.
Intrinsic Semiconductor,Extrinsic Semiconductor MCQs.
N-Type Semiconductor,P-type Semiconductor MCQs
p-n Junction MCQs
Effect of temperature on the conductivity of semiconductor MCQs

Practice it now to sharpen your concept.

PRACTICE IT NOW TO SHARPEN YOUR CONCEPT AND KNOWLEDGE

1. A silicon sample is uniformly doped with 10¹⁶ phosphorus atoms/cm³ and 2 × 10¹⁶ boron atoms/cm³. If all the dopants are fully ionized, the material is:

n-type with carrier concentration of 3 × 10¹⁶/cm³
p-type with carrier concentration of 10¹⁶/cm³
p-type with carrier concentration of 4 × 10¹⁶/cm³
Intrinsic

2. n-type semiconductors are:

Negatively charged
Produced when Indium is added as an impurity to Germanium
Produced when phosphorous is added as an impurity to silicon
None of the above

3. The probability that an electron in a metal occupies the Fermi-level, at any temperature (>0 K) is:

0
1
0.5
None of the above

4. Measurement of Hall coefficient enables the determination of:

Mobility of charge carriers
Type of conductivity and concentration of charge carriers
Temperature coefficient and thermal conductivity
None of the above

5. If the energy gap of a semiconductor is 1.1 e V it would be:

Opaque to the visible light
Transparent to the visible light
Transparent to the ultraviolet radiation
None of the above

6. The conductivity of an intrinsic semiconductor is given by (symbols have the usual meanings):

σ_i = en_i² (µ_n – µ_p)
σ_i = en_i (µ_n – µ_p)
σ_i = en_i (µ_n + µ_p)
None of the above.

7. Consider the following statements: Compared to Silicon, Gallium Arsenide (GaAs) has: 1. Higher signal speed since electron mobility is higher 2. Poorer crystal quality since stoichiometric growth difficult 3. Easier to grow crystals since the vapor pressure Arsenic is high 4. Higher optoelectronic conversion efficiency Of these statements:

1, 2, 3 and 4 are correct
1, 2 and 3 are correct
3 and 4 are correct
None of the above

8. In an intrinsic semiconductor, the mobility of electrons in the conduction band is:

Less than the mobility of holes in the valence band
Zero
Greater than the mobility of holes in the valence band
None of the above

9. The Hall coefficient of sample (A) of a semiconductor is measured at room temperature. The Hall coefficient of (A) at room temperature is 4×10^–4 m³ coulomb^–1. The carrier concentration in sample A at room temperature is:

~ 10²¹ m^–3
~ 10²⁰ m^–3
~ 10²² m^–3
None of the above

10. In a semiconductor, J, J_p and J_n indicate total diffusion current density hole current density and electron current density respectively, ∂n/∂x and ∂p/∂x are the electron and hole concentration gradient respectively in x-direction and D_p and D_n are the hole and electron diffusion constants respectively. Which one of the following equations is correct? (e denotes charge of electron.)

J_n = –eD_n(∂n/∂x) for electrons
J = –eD_p(∂p/∂x) for holes
J_p = –e D_p (∂p/∂x) – eD_n (∂n/∂x)
None of the above

11. If the drift velocity of holes under a field gradient of 100v/m is 5m/s, the mobility (in the same SI units) is

0.05
0.55
500
None of the above

12. The Hall Effect voltage in intrinsic silicon is:

Positive
Zero
Negative
None of the above

13. The Hall coefficient of an intrinsic semiconductor is:

Positive under all conditions
Negative under all conditions
Zero under all conditions
None of the above

14. Consider the following statements: pure germanium and pure silicon are examples of: 1. Direct band-gap semiconductors 2. Indirect band-gap semiconductors 3. Degenerate semiconductors Of these statements:

1 alone is correct
2 alone is correct
3 alone is correct
None of the above

15. When n_e and n_h are electron and hole densities, and µ_e and µ_n are the carrier mobilities, the Hall coefficient is positive when n_hµ_h < n_eµ_h

n_h µ_h> n_eµ_e
n_h µ_h² > n_eµ_e²
n_hµ_h < n_eµ_h
None of the above

16. A long specimen of p-type semiconductor material:

Is positively charged
Is electrically neutral
Has an electric field directed along its length
None of the above

17. The electron and hole concentrations in a intrinsic semiconductor are n_i and p_i respectively. When doped with a p-type material, these change to n and p, respectively. Then:

n + p = n_i + p_i
n + n_i = p + p_i
n_p = n_ip_i
None of the above

18. If the temperature of an extrinsic semiconductor is increased so that the intrinsic carrier concentration is doubled, then:

The majority carrier density doubles
The minority carrier density doubles
Both majority and minority carrier densities double
None of the above

19. At room temperature, the current in an intrinsic semiconductor is due to

Holes
Electrons
Holes and electrons
None of the above

20. A small concentration of minority carriers is injected into a homogeneous semiconductor crystal at one point. An electric field of 10 V.cm is applied across the crystal and this moves the minority carriers a distance of 1 cm is 20 µsec. The mobility (in cm²/volt.sec) is:

1,000
2,000
50
None of the above

21. The mobility is given by (notations have their usual meaning):

µ = V₀/E₀
µ = V₀²/E₀
µ = V₀/E₀²
None of the above

22. Hall effect is observed in a specimen when it (metal or a semiconductor) is carrying current and is placed in a magnetic field. The resultant electric field inside the specimen will be in:

A direction normal to both current and magnetic field
The direction of current
A direction anti parallel to magnetic field
None of the above

23. In a p-type semiconductor, the conductivity due to holes (σ_p) is equal to (e is the charge of hole, µ_p is the hole mobility, p0 is the hole concentration): 1.p0.e/µ_p 2.µ_p/p0.e 3.p0.e.µ_p 4.None of the above.

1 and 2
2 and 3
3 only
4 only

24. The difference between the electron and hole Fermi energies of a semiconductor laser is 1.5eV and the band gap of the semiconductor is 1.43eV. The upper and lower frequency limits of the laser will be respectively:

3.3 x 10¹⁵ and 9.9 x 10¹³ Hz
3.7 x 10¹⁶ and 3.5 x 10¹⁴ Hz
6.28 x 10¹⁷ and 3.1 x 10¹³ Hz
None of the above

25. A sample of n-type semiconductor has electron density of 6.25 x 10¹⁸/cm³ at 300K. If the intrinsic concentration of carriers in this sample is 2.5 x 10¹³/cm³, at this temperature, the hole density becomes:

10¹⁶/cm³
10⁷/cm³
10¹⁷/cm³
None of the above

26. The intrinsic carrier density at 300K is 1.5 x 10¹⁰/cm³ in silicon. For n-type silicon doped to 2.25 x 10¹⁵ atoms/cm³, the equilibrium electron and hole densities are:

n0 = 1.5 x 10¹⁶/cm³, p0 = 1.5 x 10¹²/cm³
n0 = 1.5 x 10¹⁰/cm³, p0 = 2.25 x 10¹⁵/cm³
n0 = 2.25 x 10¹⁷/cm³, p0 = 1.0 x 10¹⁴/cm³
None of the above

27. In a p-type silicon sample, the hole concentration is 2.25 x 10¹⁵/cm³. If the intrinsic carrier concentration 1.5 x 10¹⁰/cm³, the electron concentration is

10²¹/cm³
10¹⁰/cm³
10¹⁶/cm³
None of the above

28. A good ohmic contact on a p-type semiconductor chip is formed by introducing:

Gold as an impurity below the contact
A high concentration of acceptors below the contact
A high concentration of donors below the contact
None of the above

29. Measurement of Hall coefficient in a semiconductor provides information on the:

Sign and mass of charge carriers
Mass and concentration of charge carriers
Sign of charge carriers alone
Sign and concentration of charge carriers

30. Semiconductor has a

Negative temperature coefficient of resistance
Positive temperature coefficient of resistance
Constant temperature coefficient of resistance
None of these

31. To obtain n type semiconductor, the impurity added to a pure semiconductor is

Trivalent
Tetravalent
Pentavalent
None of these

32. To obtain P type semiconductor, the impurity added to a pure semiconductor is

Trivalent
Tetravalent
Pentavalent
None of these

33. An n-type semiconductor has electrons as a majority carriers, due to this material attains negative charge on it

True
False

34. A p-type and n-type semiconductor attend positive and negative charge respectively

True
False

35. In a p type semiconductor the majority carriers are

Holes
Electrons
Positive ions
Negative ions

36. When PN junction is prepared a layer is formed around the junction koda depletion layer because

P type semiconductor has holes as majority carriers
N-type semiconductor has electrons are the majority carriers
The charge Carriers are depleted in this layer
All of these

37. For Germanium PN junction the maximum value of barrier potential is

0.3 volt
0.1 volt
1.3 volt
1.7 volt

38. When a PN junction is forward biased

It offers a low resistance and the large current flows through it
It was a high resistance and small current flows through it
IT Act as an insulator and no current flows through it
The width of the depletion layer increases

39. When a PN junction is Reverse biased

The Beat of the depletion layer increases
It offers the high resistance
A small current flows through it because of minority careers careers career
All of these

40. The nucleus of a copper atom contains how many protons?

41. The net charge of a neutral copper atom is

0
+1
-1
+4

42. Assume the valence electron is removed from a copper atom. The net charge of the atom becomes

0
+1
-1
+4

43. The valence electron of a copper atom experiences what kind of attraction toward the nucleus?

None
Weak
Strong
Impossible to say

44. How many valence electrons does a silicon atom have?

45. Which is the most widely used semiconductor?

Copper
Germanium
Silicon
None of the above

46. How many protons does the nucleus of a silicon atom contain?

47. Silicon atoms combine into an orderly pattern called a

Covalent bond
Crystal
Semiconductor
Valence orbit

48. An intrinsic semiconductor has some holes in it at room temperature. What causes these holes?

Doping
Free electrons
Thermal energy
Valence electrons

49. Each valence electron in an intrinsic semiconductor establishes a

Covalent bond
Free electron
Hole
Recombination

50. The merging of a free electron and a hole is called

Covalent bonding
Lifetime
Recombination
Thermal energy

51. At room temperature an intrinsic silicon crystal acts approximately like

A battery
A conductor
An insulator
A piece of copper wire

52. The amount of time between the creation of a hole and its disappearance is called

Doping
Lifetime
Recombination
Valence

53. The valence electron of a conductor is also called a

Bound electron
Free electron
Nucleus
Proton

54. A conductor has how many types of flow?

55. A semiconductor has how many types of flow?

56. When a voltage is applied to a semiconductor, holes will flow

Away from the negative potential
Toward the positive potential
In the external circuit
None of the above

57. A conductor has how many holes?

Many
None
Only those produced by thermal energy
The same number as free electrons

58. In an intrinsic semiconductor, the number of free electrons

Equals the number of holes
Is greater than the number of holes
Is less than the number of holes
None of the above

59. Absolute zero temperature equals

-273 degrees C
0 degrees C
25 degrees C
50 degrees C

60. At absolute zero temperature an intrinsic semiconductor has

A few free electrons
Many holes
Many free electrons
No holes or free electrons

61. At room temperature an intrinsic semiconductor has

A few free electrons and holes
Many holes
Many free electrons
No holes

62. The number of free electrons and holes in an intrinsic semiconductor increases when the temperature

Decreases
Increases
Stays the same
None of the above

63. The flow of valence electrons to the left means that holes are flowing to the

Left
Right
Either way
None of the above

64. Holes act like

Atoms
Crystals
Negative charges
Positive charges

65. Trivalent atoms have how many valence electrons?

66. A donor atom has how many valence electrons?

67. If you wanted to produce a p-type semiconductor, which of these would you use?

Acceptor atoms
Donor atoms
Pentavalent impurity
Silicon

68. Holes are the minority carriers in which type of semiconductor?

Extrinsic
Intrinsic
n-type
p-type

69. How many free electrons does a p-type semiconductor contain?

Many
None
Only those produced by thermal energy
Same number as holes

70. Silver is the best conductor. How many valence electrons do you think it has?

71. Suppose an intrinsic semiconductor has 1 billion free electrons at room temperature. If the temperature changes to 75’C, how many holes are there?

Fewer than 1 billion
1 billion
More than 1 billion
Impossible to say

72. An external voltage source is applied to a p-type semiconductor. If the left end of the crystal is positive, which way do the majority carriers flow?

Left
Right
Neither
Impossible to say

73. Which of the following doesn’t fit in the group?

Conductor
Semiconductor
Four valence electrons
Crystal structure

74. Which of the following is approximately equal to room temperature?

0 degrees C
25 degrees C
50 degrees C
75degrees C

75. How many electrons are there in the valence orbit of a silicon atom within a crystal?

76. Positive ions are atoms that have

Gained a proton
Lost a proton
Gained an electron
Lost an electron

77. Which of the following describes an n-type semiconductor?

Neutral
Positively charged
Negatively charged
Has many holes

78. A p-type semiconductor contains holes and

Positive ions
Negative ions
Pentavalent atoms
Donor atoms

79. Which of the following describes a p-type semiconductor?

Neutral
Positively charged
Negatively charged
Has many free electrons

80. Which of the following cannot move?

Holes
Free electrons
Ions
Majority carriers

81. What causes the depletion layer?

Doping
Recombination
Barrier potential
Ions

82. What is the barrier potential of a silicon diode at room temperature?

0.3 V
0.7 V
1 V
2 mV per degree Celsius

83. To produce a large forward current in a silicon diode, the applied voltage must be greater than

0
0.3 V
0.7 V
1 V

84. In a silicon diode the reverse current is usually

Very small
Very large
Zero
In the breakdown region

85. Surface-leakage current is part of the

Forward current
Forward breakdown
Reverse current
Reverse breakdown

86. The voltage where avalanche occurs is called the

Barrier potential
Depletion layer
Knee voltage
Breakdown voltage

87. Diffusion of free electrons across the junction of an unbiased diode produces

Forward bias
Reverse bias
Breakdown
The depletion layer

88. When the reverse voltage increases from 5 to 10 V, the depletion layer

Becomes smaller
Becomes larger
Is unaffected
Breaks down

89. When a diode is forward biased, the recombination of free electrons and holes may produce

Heat
Light
Radiation
All of the above