| 1solid 2electrical 3conduction 4semiconductor 5vacuum 6power 7low-power 8complicated 9injection 10photoconductive | Aelectronics Bdetectors Clasers Dmaterial Esystems Ftubes Gconductivity Hproperties Idevice Jconsumption |
Make up sentences including these word-combinations and ask your partner to translate them.
7 
Speaking task. Speak on semiconductors according to the following scheme. Use some of the following expressions.
| It is well (commonly) known that | To be more accurate |
| Besides | Nevertheless |
| Therefore | At any rate |
| On the contrary | In the end |
definition c characteristic properties c classification of materials c application
Text II
Useful terms. Read and memorize the following words and word-combinations.
charge carrier
conduction band
doped semiconductor
energy gap ,
impurity
intrinsic semiconductor
N-type semiconductor
P-type semiconductor
valence band
2 
Work in pairs. Discuss with your partner the following items.
- What is an intrinsic semiconductor?
- The properties of intrinsic semiconductors
3 
Read the text and check your ideas.
Intrinsic semiconductors
A semiconductor in which the concentration of charge carriers is characteristic of the material itself rather than of the content of impurities and structural defects of the crystal is called an intrinsic semiconductor. Electrons in the conduction band and holes in the valence band are created by thermal excitation of electrons from the valence of the conduction band. Thus an intrinsic semiconductor has equal concentrations of electrons and holes. The intrinsic carrier concentration Ni is determined by equation, where E8 is the energy gap. The carrier concentration, and hence the conductivity, is very sensitive to temperature and depends strongly on the energy gap. The energy gap ranges from a fraction of 1 eV to several electronvolts. A material may have a large energy gap to be an insulator.
A silicon crystal is different from an insulator because at any temperature above absolute zero temperature, there is a finite probability that an electron in the lattice will be knocked loose from its position, leaving behind an electron deficiency called a "hole".
If a voltage is applied, then both the electron and the hole can contribute to a small current flow.
The conductivity of a semiconductor can be modeled in terms of the band theory of solids. The band model of a semiconductor suggests that at ordinary temperatures there is a finite possibility that electrons can reach the conduction band and contribute to electrical conduction.
The term intrinsic here distinguishes between the properties of pure "intrinsic" silicon and the dramatically different properties of doped n-type or p-type semiconductors.
