NCERT Solutions: Class 12 Physics Chapter 14 - Semiconductor Electronics: Materials, Devices and Simple Circuits

1. a. Electrons are majority carriers and trivalent atoms are the dopants.
2. b. Electrons are minority carriers and pentavalent atoms are the dopants.
3. c. Holes are minority carriers and pentavalent atoms are the dopants.
4. d. Holes are majority carriers and trivalent atoms are the dopants.

In n-type silicon, pentavalent dopants such as phosphorus, arsenic or antimony donate extra electrons. Therefore electrons are majority carriers and holes are minority carriers. Among the listed statements, option (c) correctly states that holes are minority carriers and the dopants are pentavalent.

1. a. Electrons are majority carriers and trivalent atoms are the dopants.
2. b. Electrons are minority carriers and pentavalent atoms are the dopants.
3. c. Holes are minority carriers and pentavalent atoms are the dopants.
4. d. Holes are majority carriers and trivalent atoms are the dopants.

A p-type semiconductor is formed by doping silicon or germanium with trivalent impurity atoms such as boron, aluminium or indium. These create holes, so holes are majority carriers and electrons are minority carriers. Therefore the correct statement from Exercise 14.1 is option (d).

1. a. (Eg)Si < (Eg)Ge < (Eg)C
2. b. (Eg)C < (Eg)Ge > (Eg)Si
3. c. (Eg)C > (Eg)Si > (Eg)Ge
4. d. (Eg)C = (Eg)Si = (Eg)Ge

The bonding electrons of carbon are more tightly bound than those of silicon and germanium, so carbon has the largest band gap. Germanium has a smaller band gap than silicon. Hence the order is $(E_g)_C>(E_g)_{Si}>(E_g)_{Ge}$.

1. a. free electrons in the n-region attract them.
2. b. they move across the junction by the potential difference.
3. c. hole concentration in p-region is more as compared to n-region.
4. d. All the above.

Diffusion occurs because carriers move from a region of higher concentration to a region of lower concentration. In an unbiased p-n junction, holes are majority carriers on the p-side, so their concentration is higher there than on the n-side. Therefore holes diffuse from p to n due to the concentration gradient.

1. a. raises the potential barrier.
2. b. reduces the majority carrier current to zero.
3. c. lowers the potential barrier.
4. d. None of the above.

In forward bias, the external voltage opposes the junction barrier field, reducing the potential barrier and allowing majority carriers to cross the junction more easily.

A half-wave rectifier gives one output pulse for each input cycle, so its output frequency is the same as the input frequency, $50\,\text{Hz}$. A full-wave rectifier gives one output pulse in each half-cycle, so it gives two pulses per input cycle. Hence the output frequency is $2\times50=100\,\text{Hz}$.