Classify each of the following as being either a p-type of a n-type semiconductor:
(i) Ge doped with In (ii) Si doped with B.

Explanation

(i) Ge doped with In. When Ge (group 14) is doped with In (group 13), out of the four valence electrons of Ge, three are shared with three electrons of In. This will result in holes in the crystal lattice of germanium and the crystals are p-type semiconductors.
(ii) B doped with Si. When B (group 13) is doped with Si (group 14), only three of the valence elctrons of silicon will be shared by the three valence electrons of boron. The presence of extra or free electrons not involved in bonding will result in n-type semiconductors.