Question

Direction: Question consists of two statements, one labeled as the 'Assertion (A)' and the other as 'Reason (R)'. Examine these two statements carefully and select the answer to this question using the codes given below:

Assertion (A): In an intrinsic semiconductor, the electron mobility in the conduction band is different from hole mobility in the valence band.

Reason (R): In an intrinsic semiconductor, electrons and holes are created solely by thermal excitation across the energy gap.

1. Both A and R are individually true and R is the correct explanation of A
2. Both A and R are individually true but R is not the correct explanation of A
3. A is true but R is false
4. A is false but R is true

Answer 1

Correct Answer - Option 2 : Both A and R are individually true but R is not the correct explanation of A

ASSERTION EXPLANATION:

In semiconductors, holes are due to the absence of electrons.

In semiconductors, the excited electron moves from the valence band to the conduction band.

This creates a free electron in the conduction band and a hole in the valence band.

The electrons therefore have better mobility as they have gained excitation energy and are further away from the region of influence of the nucleus.

The holes are under the influence of nucleic forces and also have low excitation energy, therefore less mobility. E.g.-In intrinsic silicon, at temperature 300 K; Electron mobility = 1500 cm²/(V∙s), Hole mobility = 475 cm²/(V∙s)

REASON EXPLANATION-

In the semiconductor, free charge carriers are electrons and electron holes (electron-hole pairs).

Electrons and holes are created by the excitation of electrons from the valence band to the conduction band.

An electron-hole (often simply called a hole) is the lack of an electron at a position where one could exist in an atom or atomic lattice.

It is one of the two types of charge carriers that are responsible for creating electric current in semiconducting materials. Energy for the excitation can be obtained in different ways.

1. Thermal Excitation

2. Optical Excitation

3. Excitation by Ionizing Radiation

So both statements are correct but (R) is not the correct explanation of (A).