Раздел 2 Второе занятие

109

Germanium is comparatively rare but it is rather easier to refine. It should perhaps be mentioned that the list of semiconductors given is not confined to elements; increasing attention is being paid to semi­conductor compounds such as indium antiminide and other compounds of group III with group V elements.

3. Учитесь аннотировать и реферировать.

Текст 2.1 С

а) Прочитайте текст. Выявите основную информацию каждого абзаца. Запи­шите данную информацию (в виде подлежащего и его сказуемого) на русском языке. Проверьте правильность понимания текста.

б) Прочитайте текст еще раз и составьте краткий реферат на английском язы­ке. Используйте следующие клише:

The review surveys...

The author shows the advantages of GaAs. They are ...

The conclusion is as follows...

Semiconductors as Materials

A semiconductor is a material having a resistivity in the range between conductors and insulators and having a negative temperature coefficient. The conductivity increases not only with temperature but is also affected very considerably by the presence of impurities in the crystal lattice.

Types of semiconductor material commonly used are elements falling into group IV of the Periodic Table, such as silicon or germani­um. The donor and acceptor impurities are group V and group III ele­ments, respectively, differing in valency by only one electron.

Certain compounds such as gallium arsenide (Symbol: GaAs) which has a total of eight valence electrons, also make excellent semi­conductors.

GaAs is a direct-gap III—V semiconductor that has a relatively large band gap and high carrier mobility. The relatively high carrier mobility allows the semiconductor to be used for high-speed applica­tions and because of the large energy gap it has a high resistivity that allows easier isolation between different areas of the crystal. The con-

Микроэлектроника- настоящее и будущее

duction band is a two-state conduction band; some electrons there­fore are ‘hot’ electrons, i.e. they have small effective mass and higher velocity, this resulting in the Gunn effect.

GaAs is difficult to work since diffusion of impurities into the material is extremely difficult. Epitaxy, or ion implantation must therefore be used to produce areas of different conductivity type. The main uses for gallium arsenide have been as microwave devices, such as Gunn diodes or 1MPATT diodes, but lately it has been used as a MESFET (a GaAs junction field-effect transistor) for high speed logic circuits.

4. Учитесь говорить.

14. Ответьте развернуто (2—3 предложения) на следующие вопросы:

1. What new possibilities did the advent of the transistor open?

2. Who made a great contribution to the study of semiconductor physics?

3. What is a semiconductor? Name the main properties of semicon­ductors.

4. What do they say about silicon?

5. How does a film of silicon oxide form a wafer?

6. What does oxygen concentration influence?

7. What is a fundamental ingredient in the fabrication of an integrat ed circuit?

8. What are donors?

9. What new material is under consideration?

10. In what way can GaAs compete with germanium?

14. Кратко изложите содержание основного текста. При кратком изложении тек­ста используйте следующие речевые отрезки:

1. ... has focused the attention on ...

2. ... have allowed integration of...

3. ... should enhance the speed ...

4. ... allows the chip area to increase ...

5. ... are required for interconnections...

6. ... show intrinsic properties...

7. ... was centered on two semiconductors ...