3. The concentration of added impurities is very …. .
4. The type of impurity which donates electrons to the conduction band is called … impurity.
5. When the impurities add negative carriers into the conduction band, such a crystal is called an … semiconductor.
6. When the impurity material has a deficiency of electrons in the atom, the electrons are attracted away from the valence band, leaving behind the holes. Such a crystal is called … semiconductor.
Задание 5. Переведите предложения на английский язык.
1. Чистые полупроводники мало используются: у них недостаток электронов.
2. Современные полупроводники содержат некоторые примеси.
3. Эти примеси дают преобладание либо электронов, либо дырок.
4. Процесс добавления примесей к полупроводнику называется легированием.
5. Полупроводники с посторонними примесями называются примесными полупроводниками.
6. Когда примесное вещество (материал) имеет избыток электронов в своих атомах, оно передает атомы проводящей зоне.
7. Такой кристалл называется полупроводником N- типа.
8. Когда примесное вещество имеет недостаток электронов, оно образует акцепторные уровни около валентной зоны.
9. Электроны с валентной зоны перемещаются на пустые (вакантные) места в акцепторных уровнях, образуя дырки.
10. Такой кристалл называется полупроводником P- типа.
Вариант 5
Задание 1. Переведите текст.
Transistors
Transistors are semiconductor devices with three or more electrodes. Crystal triodes and tetrodes called transistors perform many jobs formally done by vacuum tubes.
The main function of the transistor is amplification. The main part of the transistor is a semiconductor crystal called the base. Various types of semiconductor materials are used as the base: n-type and p-type. Electrons are majority carriers in n-type semiconductors (negative type) while holes are majority carriers in p-type semiconductors (positive type).
In the very close contact with the base there are two layers of different types of semiconductors, either n-type or p-type (N- emitter and N- collector, or P- emitter and P- collector). Thus, the emitter and the collector form two junctions placed back to back with the base in-between: emitter/base/collector. Correspondingly, we may have two types of transistors: N-P-N transistor and P-N-P transistor, when the conductivity of the emitter and the collector is opposite to the conductivity of the base.
The emitter junction injects the minority carriers into the base. Some of the injected carriers recombine with the majority carriers of the base. But the base layer is very thin, so that many of the carriers from the emitter are down through the base to the collector by the voltage at the collector junction which attracts them. These carries join the flow of small collector current greatly increasing it.
In the P-N-P junction transistor the minority carriers injected into the base are holes which are repelled by the positive battery terminal. The holes cross the emitter junction and get into the base region and then into the collector. As each hole reaches the collector, an electron is emitted from the negative battery terminal. Current conduction within P-N-P transistor thus takes place by the hole conduction from the emitter to collector while conduction in the external circuit is carried on by electrons. The N-P-N transistor is similar to the P-N-P transistor except that polarities are reversed. A germanium crystal is usually used as the base.
The power gain in a transistor thus may be quite high, reaching values of the order of 1000. Transistors are the most important semiconductor devices used in receivers, TV-sets, different kinds of electronic and automatic equipment.
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