Unit 1 semiconductors

1. What is a semiconductor?

Listening

3.

2) Everybody is familiar with electricity.

4) “Semi” which means not completely.

6) Most semiconductors are crystals.

Reading

4.

1. atom

2. nucleus

3. electrons

4. copper

5. crystal lattice

6. orbit

7. positive ion

8. vibrating ions

9. conductor

10. net motion

5.

1) …nearly all electrons are very tightly bound…

2) …an insulator cannot conduct any electric current…

3) …is a material that conducts current…

4) …which has almost full conductivity.

5) …behaviour opposite to that of a metal.

2. Types of semiconductors

Start here

1.

13. InP

14. SiC

15. Cu is not a semiconductor

16. GaN

17. InAs

18. GaP

19. Si

20. InSb

21. SiGe

22. C

23. GaAs

24. Ge

Listening

3.

8. True

9. False

10. True

11. False

12. False

13. False

14. True

Vocabulary

4.

6. elements – compounds

7. intrinsic – extrinsic

8. negative carriers – positive carriers

9. n-type semiconductor – p-type semiconductor

10. impure – pure

3. How semiconductors work

Reading

2.

9. The electrons in an isolated atom are organized in energy levels.

10. The outermost energy level in an isolated atom is called the valence level.

11. The electrons in this level are the ones, known as valence electrons that form bonds with neighboring atoms. Such bonds are called covalent bonds.

12. If all the neighboring atoms are of the same type, it's possible for all the valence electrons to bind with valence electrons from other atoms. When that happens, the atoms arrange themselves into structures called crystals.

13. Semiconductors are not made out of isolated atoms. They are made out of crystals.

14. In crystals and molecules atoms are arranged in energy bands.

15. The energy band formed by a series of energy levels containing valence electrons is known as valence band. Electrons in this band are more tightly bound to the individual atom than the electrons in the conduction band. However, the electrons in the valence band can still be moved to the conduction band with the application of energy, usually thermal energy.

The upper band in the solid is called the conduction band because electrons in this band are easily removed by the application of external electric fields. These electrons are free enough to move and thereby carry an electric current.

16. The energy difference between a valence band and a conduction band is called the forbidden band.

Writing

4.

• This band is fully filled with electrons.

• It is also called full band of maximum energy.

• In this band the electrons can’t gain energy from external electric field.

• Current does not flow due to such electrons.

4. Doping of semiconductors

Start here

1.

11. C. There are intrinsic and extrinsic semiconductors.

12. I. Intrinsic semiconductors do not conduct electric current.

13. E. They are generally insulators.

14. B. Doping is the process of deliberately introducing other elements into a crystal.

15. D. Extrinsic semiconductors have good conductivity.

16. F. Dopant is the element introduced by doping.

17. J. The materials chosen as suitable dopants depend on the atomic properties of both the dopant and the material to be doped.

18. G. Dopants that produce the desired controlled changes are classified as either electron acceptors or donors.

19. H. N-type semiconductors are doped with donor impurities.

20. A. P-type semiconductors are doped with acceptor impurities.

2.

intrinsic – pure, undoped

extrinsic – impure, doped, n-type, p-type, treated with impurities

3.

1. N-type silicon

2. Pure silicon

3. P-type silicon

6.

N-type semiconductor		P-type semiconductor
Majority charge carriers
Electrons		Holes
Minority charge carriers
Holes		Electorns
Group of the impurity atoms in the periodic table of elements
V	III
Impurities are called
Donor impurities	Acceptor impurities
Extra energy level
Donor level	Acceptor level
Fermi level lies in between
Conduction band and Donor level.		Valence band and Acceptor level