Question

In intrinsic semiconductor, the number of electrons in the conduction band is _______ the number of holes in the valence band.
A. equal to
B. less than
C. greater than
D. none of these

Answer 1

Hint: Intrinsic semiconductors are also known as pure semiconductors and undoped semiconductors. In these types of semiconductors there is no dopant added to it. Thus they are a pure form of semiconductor. Conduction band refers to a band of electrons where an electron jumps from the valence band leaving behind holes in the valence band. For conduction the electron must be present in the conduction band. Here we will understand about the number of electrons and holes available in respective bands.

Complete answer:
Intrinsic Semiconductors are those semiconductors in which no doping takes place. Doping refers to addition of trivalent or pentavalent impurity in the crystal lattice of semiconductors.This is done to increase the conductivity of the respective semiconductors.

The conductivity of semiconductors is influenced by the number of electrons or number of holes present in the semiconductor. Electrons are more mobile than holes, thus mobility of electrons majorly affects the conductivity of semiconductors. For the conduction process, the electrons must be present in the conduction band.

In case of intrinsic semiconductor, since there is no trivalent or pentavalent impurity is added externally so the number of electrons and holes are equal. According to which, in an intrinsic semiconductor, the number of electrons in the conduction band is equal to the number of holes in the valence band.

Therefore the correct option is A.

Note: In p-type semiconductor electrons are less as compared to holes and in n-type semiconductor electrons are more in comparison to holes. The conductivity of intrinsic semiconductors is low in comparison to extrinsic (impure) semiconductors. The overall charge of a semiconductor is always zero if it is an intrinsic or extrinsic semiconductor.