Semiconductor Materials – Exercise – 1

1. Graphite is a :

(a)  conductor
(b)  insulator
(c)  semiconductor
(d)  none of these

Answer
Answer : (a)
Explanation
No answer description available for this question. Let us discuss.
2. Doping is a process of :

(a)  purifying semiconductor material
(b)  increasing impurity percentage
(c)  removal of foreign atoms
(d)  increasing the bias potential

Answer
Answer : (b)
Explanation
No answer description available for this question. Let us discuss.
3. ……………. is an example of acceptor material.

(a)  gallium
(b)  arsenide
(c)  bismuth
(d)  antimony

Answer
Answer : (a)
Explanation
No answer description available for this question. Let us discuss.
4. Recombination of electrons and holes takes place when :

(a)  an electron falls into a hole
(b)  a positive ion and a negative ion bond together
(c)  avalanche electron becomes a conduction electron
(d)  an atom is formed

Answer
Answer : (a)
Explanation
No answer description available for this question. Let us discuss.
5. The atomic number of silicon is :

(a)  14
(b)  16
(c)  18
(d)  12

Answer
Answer : (a)
Explanation
No answer description available for this question. Let us discuss.
6. In a semiconductor, the total current is equal to :

(a)  sum of electron and hole currents flow in same direction
(b)  sum of electron and hole currents flow in opposite directions
(c)  electron current only
(d)  hole current only

Answer
Answer : (b)
Explanation
No answer description available for this question. Let us discuss.
7. The minority holes are about ……… that of electron.

(a)  half
(b)  same
(c)  twice
(d)  thrice

Answer
Answer : (a)
Explanation
No answer description available for this question. Let us discuss.
8. Germanium and silicon are :

(a)  trivalent
(b)  tetravalent
(c)  pentavalent
(d)  covalent

Answer
Answer : (b)
Explanation
No answer description available for this question. Let us discuss.
9. The volume charge density of mobile carriers is expressed in :

(a)  coulombs / cubic meters
(b)  coulombs / meters
(c)  coulombs / seconds
(d)  coulombs / volts

Answer
Answer : (a)
Explanation
No answer description available for this question. Let us discuss.
10. In a Silicon crystal, the number of covalent bonds a single atom can form is :

(a)  2
(b)  4
(c)  6
(d)  8

Answer
Answer : (b)
Explanation
No answer description available for this question. Let us discuss.
(a) (b) (c) (d) Answer : () [/su_spoiler]
Explanation
No answer description available for this question. Let us discuss.
12. An electron in a completely filled band :

(a)  contributes to the flow of electric current
(b)  does not contributes to the flow of electric current
(c)  can move but doesn’t contribute to the flow of electric current
(d)  none of these

Answer
Answer : (b)
Explanation
No answer description available for this question. Let us discuss.
13. Which electron in an element is responsible for chemical & electrical properties ?

(a)  valence electrons
(b)  revolving electrons
(c)  active electrons
(d)  passive electrons

Answer
Answer : (a)
Explanation
No answer description available for this question. Let us discuss.
14. What does a Hall Effect sensor sense ?

(a)  Temperature
(b)  Moisture
(c)  Magnetic fields
(d)  Pressure

Answer
Answer : (d)
Explanation
No answer description available for this question. Let us discuss.
15. Which of the following doesn’t have forbidden energy gap between valence band and conductor band ?

(a)  conductor
(b)  insulator
(c)  semiconductor
(d)  none of the above

Answer
Answer : (a)
Explanation
No answer description available for this question. Let us discuss.
16. While plotting the V-I characteristics of semiconductor diode, the voltage is plotted along horizontal axis and the current along the vertical axis because :

(a)  The voltage and currents are independent variables
(b)  The voltage and currents are dependent variable
(c)  The voltage is dependent and the current is independent variable
(d)  The voltage and the current are dependent variables

Answer
Answer : (d)
Explanation
No answer description available for this question. Let us discuss.
17. In a semiconductor diode, the time constant equals to :

(a)  Value of majority carrier lifetime
(b)  Value of minority carrier lifetime
(c)  Diffusion capacitance time constant
(d)  Zero

Answer
Answer : (b)
Explanation
No answer description available for this question. Let us discuss.
18. As the temperature increases in a semiconductor, the densities of the electrons and holes :

(a)  Increase
(b)  Decrease
(c)  Become equal
(d)  Can’t be defined

Answer
Answer : (a)
Explanation
No answer description available for this question. Let us discuss.
19. Drift current in the semiconductors depends upon :

(a)  only the electric field
(b)  only the carrier concentration gradient
(c)  both the electric field and the carrier concentration
(d)  both the electric field and the carrier concentration gradient

Answer
Answer : (c)
Explanation
No answer description available for this question. Let us discuss.
20. The conductivity of the intrinsic semiconductor at absolute temperature is :

(a)  1.1 eV
(b)  0.63 eV
(c)  Zero
(d)  Infinity

Answer
Answer : (c)
Explanation
No answer description available for this question. Let us discuss.
21. Doping is a process of :

(a)  Purifying semiconductor material
(b)  Increasing impurity percentage
(c)  Removal of foreign atoms
(d)  Increasing the bias potential

Answer
Answer : (b)
Explanation
No answer description available for this question. Let us discuss.
22. For a doped semiconductor material, the dynamic resistance is :

(a)  Small and can be neglected
(b)  Large and can be neglected
(c)  Small but cannot be neglected
(d)  Large but cannot be neglected

Answer
Answer : (a)
Explanation
No answer description available for this question. Let us discuss.
23. ……….. is an example of acceptor material.

(a)  Gallium
(b)  Arsenide
(c)  Bismuth
(d)  Antimony

Answer
Answer : (a)
Explanation
No answer description available for this question. Let us discuss.
(a) (b) (c) (d) Answer : () [/su_spoiler]
Explanation
No answer description available for this question. Let us discuss.
25. Graphite is a :

(a)  Conductor
(b)  Insulator
(c)  Semiconductor
(d)  None of these

Answer
Answer : (c)
Explanation
No answer description available for this question. Let us discuss.
26. Recombination of electrons and holes takes place when :

(a)  An electron falls into a hole
(b)  A positive ion and a negative ion bond together
(c)  Avalanche electron becomes a conduction electron
(d)  An atom is formed

Answer
Answer : (a)
Explanation
No answer description available for this question. Let us discuss.
27. Semiconductors are :
(I) Ohmic as they obey Ohm’s law
(II) Bipolar

(a)  Only I is true
(b)  Only II is true
(c)  Both I & II are true
(d)  Both I & II are false

Answer
Answer : (c)
Explanation
No answer description available for this question. Let us discuss.
28. Which of the following statements are correct ?
1. In semiconductor, the mobility of electrons is more than that of holes.
2. In semiconductor, when temperature increases, the resistivity also increases.
3. Metal has positive TCR.
4. In metals, thermal conductivity is inversely proportional to electrical conductivity at constant temperature.

(a)  1, 2, 3
(b)  1, 2, 4
(c)  2, 3, 4
(d)  1, 3, 4

Answer
Answer : (d)
Explanation
No answer description available for this question. Let us discuss.
29. The carrier mobility in a semiconductor is found to be 0.4 m2/VS. Its diffusion constant at 300 K will be :

(a)  0.43 m2/s
(b)  0.16 m2/s
(c)  0.04 m2/s
(d)  0.01 m2/s

Answer
Answer : (d)
Explanation
No answer description available for this question. Let us discuss.
30. The Hall coefficient of an intrinsic semiconductor is :

(a)  Positive under all conditions
(b)  Negative under all conditions
(c)  Zero under all conditions
(d)  Zero at 0°K

Answer
Answer : (d)
Explanation
No answer description available for this question. Let us discuss.
31. Consider the following statements regarding a semiconductor :
1. Acceptor level lies close to valence band.
2. Donor level lies close to valence band.
3. N-type semiconductor behaves as a conductor at 0°K.
4. P-type semiconductor behaves as an insulator at 0°K.

(a)  1 & 2 are correct
(b)  1 & 3 are correct
(c)  1 & 4 are correct
(d)  2 & 3 are correct

Answer
Answer : (c)
Explanation
No answer description available for this question. Let us discuss.
32. In a semiconductor, the total current is equal to :

(a)  Sum of electron and hole currents flow in same direction
(b)  Sum of electron and hole currents flow in opposite directions
(c)  Electron current only
(d)  Hole current only

Answer
Answer : (b)
Explanation
No answer description available for this question. Let us discuss.
33. Semiconductor materials are made up of :

(a)  Metallic bond
(b)  Ionic bond
(c)  Un-shared bond
(d)  Covalent bond

Answer
Answer : (d)
Explanation
No answer description available for this question. Let us discuss.
34. Consider the statements with respect to semiconductor breakdown.
Statement 1 : The Zener breakdown occurs in junctions which are lightly doped.
Statement 2 : The avalanche breakdown occurs in junctions, which are heavily doped.

(a)  Statements 1 & 2 are correct
(b)  Only statement 1 is correct
(c)  Only statement 2 is correct
(d)  Statements 1 & 2 are wrong

Answer
Answer : (d)
Explanation
No answer description available for this question. Let us discuss.
35. Current flow in the semiconductor slap is due to :

(a)  Drift phenomenon
(b)  Diffusion phenomenon
(c)  Recombination phenomenon
(d)  All of the above

Answer
Answer : (d)
Explanation
No answer description available for this question. Let us discuss.
36. In intrinsic semiconductor :

(a)  The electron density is twice the hole density
(b)  The electron density is thrice the hole density
(c)  The electron density is square root of the hole density
(d)  The electron density is same as the hole density

Answer
Answer : (d)
Explanation
No answer description available for this question. Let us discuss.
37. The Fermi-Dirac probability function specifying all states at energy E (electron volts) occupied under the thermal equilibrium is given by :

(a)  f(E) = KT – ln eE-Ef
(b)  f(E) = 1 + eE-Ef
(c)  f(E) = 1( 1 + e(E-Ef)/ kT)
(d)  f(E) = ((E)/Ef)e-KT

Answer
Answer : (c)
Explanation
No answer description available for this question. Let us discuss.
38. At absolute zero temperature, an intrinsic semiconductor behaves like a :

(a)  Conductor
(b)  Insulator
(c)  Semiconductor
(d)  Other metals

Answer
Answer : (b)
Explanation
No answer description available for this question. Let us discuss.
39. Germanium and silicon are :

(a)  Trivalent
(b)  Tetravalent
(c)  Pentavalent
(d)  Covalent

Answer
Answer : (b)
Explanation
No answer description available for this question. Let us discuss.
40. A semiconductor has a resistivity which :

(a)  Is smaller than 10-2 Ω-cm
(b)  Is larger than 10-2 Ω-cm
(c)  Varies between 10-2 Ω-cm and 10-9 Ω-cm
(d)  None of the above

Answer
Answer : (c)
Explanation
No answer description available for this question. Let us discuss.
(a) (b) (c) (d) Answer : () [/su_spoiler]
Explanation
No answer description available for this question. Let us discuss.
42. Intrinsic concentration of charge carriers in a semiconductor varies as :

(a)  T
(b)  T2
(c)  T3
(d)  1/T

Answer
Answer : (c)
Explanation
No answer description available for this question. Let us discuss.
43. On increasing the impurity concentration in the metal, the residual part of the resistivity :

(a)  Decreases
(b)  Increases
(c)  Remains constant
(d)  May increase or decrease

Answer
Answer : (b)
Explanation
No answer description available for this question. Let us discuss.
44. At room temperature in intrinsic germanium, there is about :

(a)  One free electron for every 109 atoms
(b)  One free electron for every 1010 atoms
(c) One free electron for every 1012 atoms
(d) One free electron for every 1015 atoms

Answer
Answer : (a)
Explanation
No answer description available for this question. Let us discuss.
45. A compensated semiconductor is doped with :

(a)  Only donor impurities
(b)  Only acceptor impurities
(c)  Both donor and acceptor impurities
(d)  Neither donor nor acceptor impurity

Answer
Answer : (c)
Explanation
No answer description available for this question. Let us discuss.
46. Donor impurity atoms in a semiconductor results in the formation of new :

(a)  Wide energy band
(b)  Narrow energy band
(c)  Discrete energy level just below conduction
(d)  Discrete energy level just above conduction

Answer
Answer : (c)
Explanation
No answer description available for this question. Let us discuss.
47. The depletion region of a semiconductor has :

(a)  Only free electrons
(b)  Only holes
(c)  Both free electrons and holes
(d)  Absence of free electrons and holes

Answer
Answer : (d)
Explanation
No answer description available for this question. Let us discuss.
48. Current flow through the semiconductor is due to :

(a)  Drift current
(b)  Diffusion current
(c)  Recombination of charges
(d)  All of the above

Answer
Answer : (d)
Explanation
No answer description available for this question. Let us discuss.
49. The depletion layer across the junction contains :

(a)  Mobile carriers
(b)  No mobile carriers
(c)  Immobile carriers
(d)  No charge carriers

Answer
Answer : (c)
Explanation
No answer description available for this question. Let us discuss.
50. For both Ge and Si, the barrier voltage decreases by about :

(a)  1 mV/°C
(b)  2 mV/°C
(c)  3 mV/°C
(d)  5 mV/°C

Answer
Answer : (c)
Explanation
No answer description available for this question. Let us discuss.