Assignment Questions : Physics : Semiconductors : Module 01 : Branch CSE & EE

 

 Assignment Questions

Semiconductors

1.    What are semiconductors?

2.    What are the types of Semiconductor?

3.    What are conductors? Give two examples Semiconductors?

4.    Give examples?

5.    What are insulators? Give two examples?

6.    What is intrinsic semiconductor?

7.    What is an extrinsic semiconductor?

8.    At what temperature would an intrinsic semiconductor behave like a perfect insulator?

9.    Distinguish between n-type and p-type semiconductors

10. Draw relevant energy level diagrams of n-type and p-type semiconductors

11. What is a hole?

12. Name the charge carriers in the following at room temperature: (i) conductor (ii) semiconductor

13. Name the majority charge carriers in p-type semiconductors.

14. Differentiate between intrinsic and extrinsic semiconductors with examples.

15. Name the factors on which electrical conductivity of a pure semiconductor depends at a given temperature.

16. Differentiate between conductor, semiconductor and insulator with suitable examples.

17. What is negative temperature coefficient of resistance?

18. How does the conductivity of a semiconductor change with rise in its temperature?

19. Write the properties of semiconductors.

20. Differentiate between Elemental semiconductors and Compound semiconductors

21. Explain direct bandgap semiconductor and indirect bandgap semiconductor

22. Differentiate between direct bandgap semiconductor and indirect bandgap semiconductor.

23. What is the basic difference between metal and semiconductor?

 

Doping

 

1.    What is doping?

1.    Name one dopant which can be used with germanium to form an n-type semiconductor.

2.    What are dopants?

3.    What are pentavalent and trivalent impurities or dopants

 

Carrier Generation and Recombination

1.    Define Carrier Generation.

2.    Define Carrier Recombination.

3.    Write differences between Carrier Generation and Recombination

4.    What is trap in semiconductor?

Diffusion  and drift

1.    Define drift and drift current in semiconductors.

2.    Define diffusion and diffusion current in semiconductors.

3.    What is diffusion length.

4.    Differentiate between drift and diffusion currents.

5.    Explain carrier transport in semiconductors.

6.    What is drift and diffusion current in semiconductor?

7.   What is the drift voltage?

8.   What does the diffusion coefficient mean?

9.    Give the expression for drift current density µ due to electron.

10. write the equation for drift current density due to holes.

11. write the equation for diffusion current density due to electron.

12. write the expression for diffusion current density due to holes.

13. Explain Fick's Law

Fermi energy

1.    What is Fermi level?

2.    What is Fermi energy?

3.    Explain thermal equilibrium in in semiconductors.

4.    write the equation for the Fermi level energy in n – type semiconductor.    

5.   What is Fermi’s golden rule?

6.    Discuss in detail the dependence of Fermi level on carrier concentration and temperature.

7.    What do you mean by occupation probability?

8.    Write the expression for the Fermi level energy in n – type semiconductor.

Energy bands in Solids : Theory and Concept Illustrations with Solved Problems

Energy bands in Solids

Energy band model

Energy band model is an scheme to describe the conductivity of conductors, insulators, and semiconductors and differentiate them on the basis of energy of electrons of an atom in solids. It provides complete description and behaviour of the conductors, semiconductors and insulators.

Atoms in a crystal interact leading to splitting of energy levels. The amount of interaction is proportion to the atomic spacing. 

Energy band model consists of two energy bands

•     valence band
•    conduction band

And the energy gap between valence band and conduction band is called band gap.
The width of forbidden energy gap between valence band and conduction band distinguishes conductors, semiconductors and insulators from each other.

Important Points:

• The range of energies from the lowest to the highest level of band is called width of a band.
• Energy of inner shell's electrons are split to a lesser degree. 
• Inner shell's electrons energy form a narrow band. 
• Electron from inner shells donot take part in conduction.
• Energy levels of valence electrons are split more and form wider band.
• Electrons start occupying a band from the lowest energy level and fill the levels one after the other in ascending order of energy.
• when all the energy levels are occupied by electrons, the band is said to be full. In the case of non-availability of electrons of electrons, the band gets partly filled.
• when there are no electrons to occupy the energy levels, the energy band remains vacant or empty.