Question

If indium is added in small quantity to germanium metal, we get a/an:
(A) n-type semiconductor
(B) p-type semiconductor
(C) rectifier
(D) insulator

Answer 1

As we know that materials which have electrical and thermal conductivity less than the metals but more than non-metals are called semiconductors. In order to increase their conductivity, we need to introduce a few impurities in it. When a pentavalent impurity is added, then it is called n-type semiconductor whereas when a trivalent impurity is added, then it is called p-type semiconductor.

Complete answer:
Let us understand the chemistry of semiconductors as follows:-
-The materials which have moderate conductivity between metals and non-metals are known as semiconductors. To increase their conductivity, we need to introduce few impurities which lead to the formation of 2 types of conductors as discussed below:-
(a) p-type semiconductors: These are the semiconductors in which trivalent impurities are added such as elements of 13-group of the periodic table. These trivalent impurity atoms are also called Acceptor atoms because they lead to the increment of holes which act as charge carriers in case of p-type conductors.
(b) n-type semiconductors: These are the semiconductors in which pentavalent impurities are added such as elements of 15-group of the periodic table. These pentavalent impurity atoms are also called Donor atoms because they lead to the increment of electrons which act as charge carriers in case of p-type conductors.
-Indium being the element of a 13-group of periodic table is also a trivalent atom. When it is introduced in the germanium (Ge) semiconductor, it cannot complete all the valencies of the adjacent Ge atoms which lead to the formation of holes that act as charge carriers and hence we get a p-type conductor.

Therefore, the correct option is: (B) p-type semiconductor

Note:
-Pure semiconductors are also known as intrinsic semiconductors and those semiconductors which are doped with impurities are known as extrinsic semiconductors.
-In case of p-type conductors, the majority of charge carriers move from high potential to low potential whereas in case of n-type conductors, the majority of charge carriers move from low potential to high potential.