Question

In p-type semiconductors, holes are:
A) Majority carriers
B) Minority carriers
C) Absent
D) None of the above.

Answer 1

Hint:At room temperature, the conductivity of an intrinsic semiconductor is very low. Using this type of semiconductor, important electronic devices cannot be developed. Hence, there is a necessity of increasing their conductivity. This can be done by adding suitable impurities to a pure semiconductor.

Complete step by step answer:

The process of adding impurities to a pure semiconductor to increase its conductivity is called doping.
Added impurities are called dopants.
There are two types of dopants namely pentavalent dopants and trivalent dopants. The pentavalent has 5 valence electrons and trivalent dopants have 3 valence electrons.

The essential requirements for the doping process:

The presence of the dopant atoms should not disturb the crystal lattice of the pure semiconductor.
The size of the dopant should equal the size of the original semiconductor atom.
The dopants are added in very small quantities.

Depending upon the type of impurity added, the extrinsic semiconductor is classified into two types:

N-type semiconductor
P-type semiconductor.

Here we will be discussing p-type semiconductors.

A P-type semiconductor is obtained when a controlled amount of suitable trivalent impurity is added to a pure semiconductor. The addition of trivalent impurity provides a large number of holes in the semiconductor. Impurities which can produce p-type semiconductor are called acceptor impurities because the holes created can accept the electrons.
When a small amount of trivalent impurities like aluminum or gallium is added to germanium crystal, there exist a large number of holes in the crystal. Gallium is trivalent, that is its atom has three valence electrons. All the three valence electrons of gallium form a covalent bond with germanium atoms. And the fourth bond is incomplete and this gives rise to a hole.

By observing all these explanations, we can say in p-type semiconductors, holes are majority carriers.

Therefore, the correct option is (A).

Note:
-In p-type semiconductors, electrons are the minority charge carriers.
-In a p-type semiconductor, at room temperature, there are a large number of holes in the valence band and the conductivity of a p-type semiconductor increases significantly.