Question

The valency of impurity element for making p-type semiconductor is
(A) $5$
(B) $3$
(C) $4$
(D) $7$

Answer 1

Hint: A p-type semiconductor refers to the semiconductor, in which the majority charge carriers are the holes. A natural semiconductor contains an equal number of the holes and the electrons. But for making holes as a majority, we dope it with a suitable impurity element.

Complete step by step answer
A natural semiconductor, also known as an intrinsic semiconductor, has a very low conductivity at the room temperature. So no electrical devices can be developed from them. Therefore we increase the conductivity of the intrinsic semiconductor by doping it with the impurity element. The doped semiconductor is known as the extrinsic semiconductor.

Now, due to doping the number of charge carriers increases in the semiconductor. We know that there are two kinds of charge carriers; the electrons and the holes. One of these charge carriers becomes the majority charge carrier after doping. The semiconductor having electrons as the majority charge carriers are known as n-type semiconductors and that having holes as majority charge carriers are known as p-type semiconductors.

For the formation of a p-type semiconductor, we have to use an element which has one valence electron less than that of the semiconductor elements, i.e., $3$. This is because in this case the element will form bonds with the three of the neighbouring atoms and the fourth bond will have a vacancy of one electron, and hence it will act as a hole.

So the correct answer is option B.

Note
The doping of a semiconductor doesn’t affect its electrical neutrality. The intrinsic semiconductor is neutral, and so are the dopants. Hence, the extrinsic semiconductor formed is also electrically neutral.