Class 12 Physics Chapter 14 NCERT Solutions: Semiconductor Electronics Guide

Q.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.

Ans.14.1 The correct statement is (c ).

In an n-type silicon, the electrons are the majority carrier, while the holes are the minority carriers. An n-type semiconductor is obtained when pentavalent atoms, such as phosphorous, are doped in silicon atoms.

Ans. 14.2 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.

Q.14.3 Carbon, silicon and germanium have four valence electrons each. These are characterized by valence and conduction bands separated by energy band gap respectively equal ${\left({\mathit{E}}_{\mathit{g}}\right)}_{\mathit{c}}$ to ${\left({\mathit{E}}_{\mathit{g}}\right)}_{\mathit{S}\mathit{i}}$ ,  and ${\left({\mathit{E}}_{\mathit{g}}\right)}_{\mathit{G}\mathit{e}}$ . Which of the following statements is true?

(a) $\mathit{}{\left({\mathit{E}}_{\mathit{g}}\right)}_{\mathit{S}\mathit{i}}$ < ${\left({\mathit{E}}_{\mathit{g}}\right)}_{\mathit{G}\mathit{e}}$ < ${\left({\mathit{E}}_{\mathit{g}}\right)}_{\mathit{c}}$

(b) ${\left({\mathit{E}}_{\mathit{g}}\right)}_{\mathit{c}}\mathit{}$ < ${\left({\mathit{E}}_{\mathit{g}}\right)}_{\mathit{G}\mathit{e}}$  > ${\left({\mathit{E}}_{\mathit{g}}\right)}_{\mathit{S}\mathit{i}}$

(c) ${\left({\mathit{E}}_{\mathit{g}}\right)}_{\mathit{c}}$  > ${\left({\mathit{E}}_{\mathit{g}}\right)}_{\mathit{S}\mathit{i}}$ > ${\left({\mathit{E}}_{\mathit{g}}\right)}_{\mathit{G}\mathit{e}}$

(d) ${\left({\mathit{E}}_{\mathit{g}}\right)}_{\mathit{c}}$  = ${\left({\mathit{E}}_{\mathit{g}}\right)}_{\mathit{S}\mathit{i}}$  = ${\left({\mathit{E}}_{\mathit{g}}\right)}_{\mathit{G}\mathit{e}}$

Ans.14.3 The correct statement is (c).

Of the three given elements, the energy band gap of carbon is the maximum and germanium is the least. The energy band gap of these elements is related to  ${\left(E_g\right)}_c$ >  ${\left(E_g\right)}_{Si}$ >  ${\left(E_g\right)}_{Ge}.$

Q.14.4 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.

Ans.14.4 The correct statement is (c).

The diffusion of charge carriers across a junction takes place from the regions of higher concentration to the region of lower concentration. In this case, the p-region has greater concentration of holes than the n-region. Hence, in an unbiased p-n junction, holes diffuse from the p-region to the n-region.