The Movement of Holes

If a silicon crystal is heated, the breaking of covalent bonds is taking place. Figures of exercise 2 in Unit 7 show what occurs in the atoms of the crystal. In one figure we see that one covalent bond has broken, one electron has freed itself, and a hole has appeared at point A. In the next figure we see that a second hole at point B has appeared. Now there are two free electrons. The second electron is passing the first hole. It has been attracted by the hole and there is no hole at point A. It seems that the hole has moved from position A to position B.

Then we see that the third electron has freed itself and recombination has taken place at some other point where the hole has disappeared.

The movement of electrons and holes is random.

But if some voltage is applied, then the electrons begin to move in one direction and the holes begin to move in the opposite direction. Thus, conduction may take place in a pure semiconductor. Such a conduction is known as intrinsic conduction. The increase of temperature of the semiconductor increases its conductivity.

16. Read the text again and complete the sentences with the correct ending.

1. If a silicon crystal is heated, …

2. As a result of breaking of one covalent bond, one electron …

3. The second electron is passing the first hole and it …

4. The third electron has freed itself and …

5. If some voltage is applied …

6. The conduction which takes place in a pure semiconductor is known as …

7. The increase of temperature of the semiconductor …

17. Work in pairs. Ask your partner some questions based on the text. Make sure you use the correct auxiliary verb.

For example:

The breaking of covalent bonds takes place (Where?)

Where does the breaking of covalent bonds take place?

1. In one figure we see that one covalent bond has broken (What …?) – …

2. If some voltage is applied, then the electrons begin to move (How?) – …

3. The increase of temperature changes the features of a semiconductor (How?) – …

4. Conduction may take place in (Where?) – …

SPEAKING

18. Summarize the text “The Movement of Holes” in 100 words using the figures of exercise 2:

Describe the process of recombination to your group mate using active terms of the Unit and the Present Perfect

Try to work as an interpreter. Translate the explanation of the way the electron frees itself given by your group mates from Russian into English.

21. Translate the text, which contains additional information about electron-hole movement with a dictionary in writing. Pay attention to the new words and the use of the Present Perfect.