2018-01-08
1045
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.
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
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.
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 | |
UNIT 2
DIODE
WHAT IS A DIODE?
Listening
5.
9. False
10. True
11. True
12. True
13. False
14. False
15. False
16. False
Reading
7.
1) forward biased
2) reverse biased
3) amount
4) diode
5) forward voltage drop
6) backward
7) peak inverse voltage
8) current
Vocabulary
8.
| diode диод | p-n juction электро-дырочный переход | anode анод | forward bias прямое смещение | reverse voltage обратное напряжение |
| cathode катод | current rating номинальный ток | lead подводящий провод | circuit цепь | threshold порог |
