Question

In which of the following statements, the obtained impure semiconductor is of p-type?
A. Germanium is doped with bismuth
B. Silicon is doped with antimony
C. Germanium is doped with gallium
D. Silicon is doped with phosphorus.

Answer 1

Hint: We must know that doping a particular semiconductor element with another will result in an impure semiconductor. P-type semiconductors have trivalent impurity and because of this we have an excess number of holes in this type of semiconductor. The current that flows in this type of conductors is due to the movement of holes inside the material.

Complete step by step answer:
The material which has conductivity in the range between that of conductors and insulators is called semiconductor. Semiconductors are of two types – one is intrinsic semiconductor and the other is extrinsic semiconductor.
Intrinsic semiconductors are pure elements such as silicon.
Extrinsic semiconductors made by doping other impurities to improve its conductivity.
Extrinsic semiconductors are of n-type or p-type depending on the property of the impurity. In n-type semiconductor we add pentavalent impurity and in p-type semiconductor we add trivalent impurity.
A p-type semiconductor is produced by doping a 14-group element with a 13-group element as a 14 group element have 4 valence electrons and a 13 group element has 3 valence electrons.
In the above question, germanium is a 14-group element and gallium is a 13-group element. So, when germanium is doped with gallium, we will get a p-type semiconductor.

So, the correct answer is “Option C”.

Note: In a p-type semiconductor, both the electrons and holes are charge carriers but the number of holes is very much larger when compared to the number of electrons. The conductivity of a material can be defined as the extent to which the material can conduct electricity. For an intrinsic conductor, the number of electrons and the number of holes are equal.