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SPECIALIST READING. 14. Read the text “Operation of a Semiconductor Junction Diode” and draw a scheme of 1) a forward-biased and 2) a reverse-biased semiconductor diode.

14. Read the text “Operation of a Semiconductor Junction Diode” and draw a scheme of 1) a forward-biased and 2) a reverse-biased semiconductor diode.

When P- and N-type silicon are joined a junction is created. This two-element device has a unique characteristic: the ability to pass current readily in one direction but not in the other.

Let us apply the theory of negative and positive carrier to this diode. Consider first the effect of connecting a battery across this diode with the polarity shown in this figure.

1) Free electrons enter the N-tуре silicon. These electrons repel the free electrons in the N-tуре silicon, and the free electrons move toward the P-N junction.

The holes in the P-type silicon are repelled by the positive terminal of the battery and also move toward the P-N junction, where combination of free electrons and holes takes place. The current carriers lost in these combinations are replaced by new current carriers resulting from separation of electron-hole pairs.

The free electrons created in the P-type silicon are attracted to the positive terminal and flow in the external circuit as shown. The process is continuous, and current flow is maintained. Moreover, if the voltage at the terminal is increased, current flow in the diode increases.

The manner of connecting the negative battery terminal to the N-type silicon and the positive battery terminal to the P-type silicon results in current flow and is called forward bias. Since current flows in this connection, the diode is said to have a low forward resistance.

In the reverse-bias connection the positive terminal of the battery attracts free electrons in the N-type silicon away from the P-N junction.

2) The negative terminal of the battery attracts the holes in the P-type silicon away from the P-N junction.

Hence there are no combinations of free electrons and holes. Thus the majority current carriers in the diode do not maintain current flow. In this reverse-bias connection there is a minute current in the diode. This current is due to the minority carriers, i.e. due to the holes in the N-type silicon and free electrons in the P-type silicon. For the minority carriers, battery polarity is correct (зд. достаточный) to maintain current flow. Only a few microamperes of current flow as a result of the minority carriers. The reverse-bias connection results in a high reverse resistance in the diode.

There is a limit not only to the forward-bias but also to the reverse-bias voltage which may be placed across the diode. If the forward or reverse bias is increased beyond its limiting value, there is a sharp increase in forward or reverse current. This increase may destroy the diode by overheating due to excessive current flow.

15. Study the text and translate the following:

- способность хорошо проводить ток

- применять теорию (к)

- положительные и отрицательные носители зарядов

- подсоединить батарею к диоду

- двигаться к электронно-дырочному переходу

- замещаться новыми носителями заряда

- получающиеся в результате разделения связанной электронно-дырочной пары

- двигаться во внешней цепи

- поддерживать движение тока

- способ соединения

- приводить к результату

- прямое/обратное смещение

- прямое сопротивление

- отсюда/поэтому

- незначительный ток

- этот ток образуется благодаря неосновному носителю зарядов

- резкое повышение тока

- избыточный ток

16. Look at the English variant of the words of the previous exercise for 30 seconds, divide into three groups and see which group can remember more.