4 One of the crucial keys to solid state electronics is the nature of the P-N junction. When p-type and n-type materials are placed in contact with each other, the junction behaves very differently than either type of material alone. Specifically, current will flow readily in one direction but not in the other, creating the basic diode. This non-reversing behavior arises from the nature of the charge transport process in the two types of materials. The open circles on the left side of the junction above represent "holes" or deficiencies of electrons in the lattice which can act like positive charge carriers. The solid circles on the right of the junction represent the available electrons from the n-type dopant. Near the junction, electrons diffuse across to combine with holes, creating a " depletion region ". The energy level sketch is a way to visualize the equilibrium condition of the P-N junction. The upward direction in the diagram represents increasing electron energy.
Figure 6. P-N Junction
5 When a p-n junction is formed, some of the free electrons in the n-region diffuse across the junction and combine with holes to form negative ions. In so doing they leave behind positive ions at the donor impurity sites.
Figure 7. Depletion region
Complete the following sentences according to the information given in the text.
1 Doping of semiconductors is
2 The material is said to be p-type if
3 Due to the thermal effects
4 Current in p-n junction
5 Depletion region is
4 
Work in pairs. Put the questions to the underlined words in the text and let your partner give the answers.
Complete the word building table.
| Verb | Noun | Adjective | Adverb |
| to add | additional | ||
| creativity | creatively | ||
| to free | freely | ||
| production | productive | ||
| to ease | ease | ||
| conductive | conductively | ||
| diffusible | |||
| to direct | direct | ||
| depletable |
Paraphrase the following expressions using the information from the text.
The way of doping
A material without impurities
Valence admixture
Lack of negative electric charges
Substances brought together
Make up sentences including word-combinations from the previous exercise.
8 
Writing. Using the illustrations describe the depletion region and write a passage about it.
A 
| B 
| C 
|
|
9 
Speaking task. Speak on the doping of semiconductors. While speaking use the following expressions.
As a matter of fact
Actually
Indeed
Generally
On the whole
Regardless of the fact that
Even though
With reference to
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