Electric conduction in a semiconductor takes place due to: 

Concept:

Semiconductors are the material which have the conductivity in between the conductors (mostly metals) and the insulators. Semiconductors are of two types:

p-type semiconductor:

• A p-type semiconductor is an intrinsic semiconductor doped with boron or indium.

• The majority of carriers in p-type semiconductors are holes.

• Electrons are minority carriers in a p-type semiconductor.

• In a p-type semiconductor, the hole density is much greater than the electron density.

• The acceptor energy level of the p-type is close to the valency bond and away from the conduction band.

• In an n-type semiconductor an intrinsic semiconductor doped with phosphorus or antimony as impurity.

n-type semiconductor:

• The majority of charge carriers in n-type semiconductors are electrons.

• Holes are minority carriers in a n type semiconductor.

• In the n type of semiconductor, the electron density is much greater than the hole density.

• The donor energy level of n-type is close to the conduction band and away from the valency band.

The cause of electrical conduction in semiconductors is due to the movement of holes in the valence band and the movement of the electrons in the conduction band. When electric field is applied then as a result the electrons will start moving in the conduction band in the direction opposite to that of electric field.

Hence, the correct answer is Option-4-both holes and electrons.