This set of Physics Multiple Choice Questions & Answers (MCQs) focuses on “Intrinsic Semiconductor”.
1. An intrinsic semiconductor, at the absolute zero temperature, behaves like which one of the following?
c) n-type semiconductor
d) p-type semiconductor
Explanation: At the absolute zero temperature, an intrinsic semiconductor behaves like an insulator. It is an undoped semiconductor. An intrinsic semiconductor at absolute zero temperature has electrons only in the valence band.
2. The probability of electrons to be found in the conduction band of an intrinsic semiconductor at finite temperature is which of the following?
a) Increases exponentially with the increasing bandgap
b) Decreases exponentially with the increasing bandgap
c) Decreases with increasing temperature
d) Is independent of the temperature and the bandgap
Explanation: At a finite temperature, the probability of jumping an electron from the valence band to the conduction band decreases exponentially with the increasing bandgap (Eg). The other options are not valid.
3. Which of the following statements is not true?
a) The resistance of intrinsic semiconductor decreases with the increase of temperature
b) Doping pure Si with trivalent impurities gives p-type semiconductors
c) The majority carriers in n-type semiconductors are holes
d) A p-n junction can act as a semiconductor diode
Explanation: The majority charge carriers in n-type semiconductors are electrons, not holes. It is made by adding an impurity to a pure semiconductor such as silicon or germanium. All the other statements are true.
4. Holes are charge carriers in which one of the following?
a) Intrinsic semiconductors
b) Ionic solids
c) n-type semiconductors
Explanation: In intrinsic semiconductors, the holes are charge carriers.
For intrinsic semiconductors, the expression is given as:
nh = ne.
5. In semiconductors at a room temperature correspond to which among the following?
a) The valence band is partially empty and the conduction band is partially filled
b) The valence band is filled and the conduction band is partially filled
c) The valence band is filled
d) The conduction band is empty
Explanation: When the semiconductors are at room temperature, the valence band of the semiconductor is partially empty, whereas the conduction band of the semiconductor is partially filled with electrons.
6. A semiconductor is damaged by a strong current because of a lack of free electrons.
Explanation: No, this statement is false. When a strong current is passed through a semiconductor, this causes many covalent bonds to break up due to heating and thereby to liberate a large number of free electrons.
7. At absolute zero, Si acts as which of the following?
Explanation: At absolute zero temperature, silicon acts as an insulator. This is because, at absolute zero, silicon does not have any free electrons in its conduction band, and therefore, acts as an insulator in the absence of free electrons.
8. Choose the false statement from the following.
a) In conductors the valence and conduction band overlap
b) Substances with an energy gap of the order of 10 eV are insulators
c) The resistivity of a semiconductor increases with increase in temperature
d) The conductivity of a semiconductor increases with increase in temperature
Explanation: Resistivity of a semiconductor and temperature are inversely proportional to each other. When the resistivity of a semiconductor decreases, the temperature increases. Semiconductors have bulk resistivity in the range of 103-ohm cm.
9. At which temperature, a pure semiconductor behaves slightly as a conductor?
a) Low temperature
b) Room temperature
c) High temperature
Explanation: A pure semiconductor behaves slightly as a conductor at high temperatures. As temperature increases, resistivity decreases, and since resistivity and conductivity are inversely proportional to each other, the conductivity of the intrinsic semiconductor increases with an increase in temperature.
10. In a pure semiconductor crystal, if current flows due to breakage of crystal bonds, then what is the semiconductor called?
c) Intrinsic semiconductor
d) Extrinsic semiconductor
Explanation: Pure semiconductors are called intrinsic semiconductors. The number of electrons in the conduction band will be equal to the number of holes in the valence band. Intrinsic semiconductors are the semiconductors which are not doped with any impurities.
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