MCQ-3
This set of Class 12 Physics Chapter 14 Multiple Choice Questions & Answers (MCQs) focuses on “Extrinsic Semiconductor”.
1. On doping germanium metal, with a little amount of indium, what does one get?
a) Intrinsic semiconductor
b) Insulator
c) n-type semiconductor
d) p-type semiconductor
Answer: d
Explanation: Indium impurity in germanium produces p-type semiconductors. A trivalent impurity added to germanium produces a p-type semiconductor. Trivalent impurities such as boron, indium, and gallium are called acceptor impurity.
2. In a pure semiconductor crystal, if current flows due to breakage of crystal bonds, then what is the semiconductor is called?
a) Acceptor
b) Donor
c) Intrinsic semiconductor
d) Extrinsic semiconductor
Answer: c
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 also called undoped and i-type semiconductors.
3. Which of the following, when added as an impurity, into the silicon, produces n-type semiconductor?
a) Phosphorous
b) Aluminum
c) Magnesium
d) Sulfur
Answer: a
Explanation: As phosphorous is pentavalent, it produces n-type semiconductor when added to silicon. They are called donor impurities. By adding phosphorus, extra valence electrons are added that become unbonded from individual atoms.
4. In n-type semiconductors, which one is the majority charge carriers?
a) Holes
b) Protons
c) Neutrons
d) Electrons
Answer: d
Explanation: In n-type semiconductors, electrons are majority charge carriers. It is made by adding an impurity to a pure semiconductor. This is the opposite scenario of p-type semiconductors where electrons are the minority charge carriers.
5. A small impurity is added to germanium to get a p-type semiconductor. Identify the impurity?
a) Bivalent substance
b) Trivalent substance
c) Pentavalent substance
d) Monovalent substance
Answer: b
Explanation: A trivalent impurity added to germanium produces a p-type semiconductor. Trivalent impurities such as boron, indium, and gallium are called acceptor impurity. These can be added to germanium in order to obtain a p-type semiconductor.
6. Boron when added as an impurity, into the silicon, produces n-type semiconductor.
a) True
b) False
Answer: b
Explanation: When a pentavalent impurity is added as an impurity to silicon, it produces n-type semiconductor. In n-type semiconductors, electrons are majority charge carriers, whereas the holes are minority charge carriers.
7. Identify the property which is not characteristic for a semiconductor?
a) At a very low temperature, it behaves like an insulator
b) At higher temperatures, two types of charge carriers will cause conductivity
c) The charge carriers are electrons and holes in the valence band at higher temperatures
d) The semiconductor is electrically neutral
Answer: c
Explanation: In a semiconductor, electrons are the charge carriers in the conduction band and holes are the charge carriers in the valence band at higher temperatures. The other statements are not valid.
8. The n-type semiconductor is which of the following?
a) Positively charged
b) Negatively charged
c) Neutral
d) Positive or negative depending upon doping materials
Answer: c
Explanation: Semiconductors maintain their electrical neutrality even after doping. This is achieved by adding an impurity to a pure semiconductor in order to obtain an n-type semiconductor.
9. The dominant contribution to current comes from holes in case of which of the following?
a) Metals
b) Intrinsic semiconductors
c) p-type extrinsic semiconductors
d) n-type extrinsic semiconductors
Answer: c
Explanation: Holes are the majority charge carriers in p-type extrinsic semiconductors. Trivalent impurities such as boron, indium, and gallium are called acceptor impurity. Also, in p-type semiconductors, electrons are the minority charge carriers.
10. In a p-type semiconductor, germanium is doped with which of the following?
a) Gallium
b) Copper
c) Phosphorous
d) Nitrogen
Answer: a
Explanation: Substances such as gallium, boron, and aluminum are all trivalent atoms. These are called acceptor impurities and they produce p-type semiconductors. Therefore, germanium is doped with gallium in a p-type semiconductor.