Read the text again and select from the multiple choice the only solution to each problem.

1. If you want to get a semiconductor of P-type, what impurity material will you introduce into a silicon crystal?

a) phosphorus c) arsenic

b) antimony d) gallium

2. What valency does silicon have?

a) It is univalent c) trivalent

b) bivalent d) tetravalent

3. How many electrons may a pentavalent material introduce into the crystal lattice of silicon?

a) 0 c) 2

b) 1 d) 3

4. Characterize the bond between the arsenic nucleus and the electron, which is going to free itself.

a) strong c) loose

b) very strong d) very loose

5. According to Reserphord an atom of each substance consists of three elements, but the fourth element, which has a great role in semiconductor conductivity is mentioned in the text. Mark the odd word from the list below.

a) proton c) hole

b) neutron d) electron

6. If we need a P-type semiconductor, we will use an impurity called …

a) donor c) extrinsic

b) acceptor d) intrinsic

7. Which chemical element is not mentioned in the text?

a) silicon c) gallium

b) aluminium d) arsenic

Read the text “Semiconductors of N-type and P-type” again and answer the following questions.

1. How many valency electrons should an acceptor impurity have?

2. Why are semiconductors called N-type and P-type?

3. What chemical properties does silicon have?

4. Why do we usually use the elements of group III and V as impurities for silicon crystal to cause a certain type of conductivity?

5. Is the process of recombination possible in an N-type semiconductor? Why?

6. Which types of charge carriers have you met in the text?

7. How do chemists and physicists call the bonds between impurity electrons and neighbouring atoms of the material?

8. What does the valency of an element show us in general?

9. Can you name some other chemical elements which may be used as impurities?

10. Is it correct to use the terms majority/minority charge carriers considering pure silicon? Why?

Complete the sentences with the correct ending according to the text.

1. If we add a small amount of arsenic to silicon, …

2. As the fifth electron of arsenic attached to the nucleus very loosely …

3. In N-type semiconductor the electrons are …, and the holes are …

4. Each atom of arsenic will add …

5. Sometimes an electron and a hole meet and …

6. If a group III element is introduced into a silicon crystal, …

7. Gallium has …

8. Each atom of gallium introduces …

9. Gallium doped to silicon is the type of impurity called …

10. Introducing gallium into silicon results in the semiconductor, which is known …

<== попередня сторінка	\|	наступна сторінка ==>
Read the text “Semiconductors of N-type and P-type”. Mark the following sentences as true (T) or false (F).	\|	SPEAKING

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