Semiconductor Electronics Materials Devices and Simple Circuits
Exercises
14.1 In an n-type silicon, which of the following statement is true:
(a) Electrons are majority carriers and trivalent atoms are the dopants.
(b) Electrons are minority carriers and pentavalent atoms are the dopants.
(c) Holes are minority carriers and pentavalent atoms are the dopants.
(d) Holes are majority carriers and trivalent atoms are the dopants.
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Answer
The correct statement is (c).
In an n-type silicon, the electrons are the majority carriers, while the holes are the minority carriers. An n-type semiconductor is obtained when pentavalent atoms, such as phosphorus, are doped in silicon atoms.
14.2 Which of the statements given in Exercise 14.1 is true for p-type semiconductos.
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Answer
The correct statement is (d).
In a p-type semiconductor, the holes are the majority carriers, while the electrons are the minority carriers. A p-type semiconductor is obtained when trivalent atoms, such as aluminium, are doped in silicon atoms.
14.3 Carbon, silicon and germanium have four valence electrons each. These are characterised by valence and conduction bands separated by energy band gap respectively equal to $\left(E _{\mathrm{g}}\right) _{\mathrm{C}},\left(E _{\mathrm{g}}\right) _{\mathrm{Si}}$ तथा $\left(E _{\mathrm{g}}\right) _{\mathrm{Ge}}$ Which of the following statements is true?
(a) $\left(E _{g}\right) _{\mathrm{Si}}<\left(E _{g}\right) _{\mathrm{Ge}}<\left(E _{g}\right) _{\mathrm{C}}$
(b) $\left(E _{g}\right) _{\mathrm{C}}<\left(E _{g}\right) _{\mathrm{Ge}}>\left(E _{g}\right) _{\mathrm{Si}}$
(c) $\left(E _{g}\right) _{\mathrm{C}}>\left(E _{g}\right) _{\mathrm{Si}}>\left(E _{g}\right) _{\mathrm{Ge}}$
(d) $\left(E _{g}\right) _{\mathrm{C}}=\left(E _{g}\right) _{\mathrm{Si}}=\left(E _{g}\right) _{\mathrm{Ge}}$
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# Content Missing14.4 In an unbiased p-n junction, holes diffuse from the p-region to n-region because
(a) free electrons in the n-region attract them.
(b) they move across the junction by the potential difference.
(c) hole concentration in p-region is more as compared to n-region.
(d) All the above.
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# Content Missing14.5 When a forward bias is applied to a p-n junction, it
(a) raises the potential barrier.
(b) reduces the majority carrier current to zero.
(c) lowers the potential barrier.
(d) None of the above.
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Answer
The correct statement is (c).
When a forward bias is applied to a p-n junction, it lowers the value of potential barrier. In the case of a forward bias, the potential barrier opposes the applied voltage. Hence, the potential barrier across the junction gets reduced.
14.6 In half-wave rectification, what is the output frequency if the input frequency is $50 \mathrm{~Hz}$. What is the output frequency of a full-wave rectifier for the same input frequency.
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Answer
Input frequency $=50 \mathrm{~Hz}$
For a half-wave rectifier, the output frequency is equal to the input frequency.
$\therefore$ Output frequency $=50 \mathrm{~Hz}$
For a full-wave rectifier, the output frequency is twice the input frequency.
$\therefore$ Output frequency $=2 \times 50=100 \mathrm{~Hz}$
