Semiconductor Devices

Semiconductor devices are composed of solid-state elements. Germanium and silicon are the basic elements used for manufacturing these devices. But silicon has much better characteristics.

In pure form these materials may be defined as insulators. Doping the semiconductor material with a small amount of impurity provides a radical change in the conduction of current, making this material a good current conductor.

Acceptor impurity is used to obtain p-type semiconductor material. N-type material is obtained after introducing donor impurity. The majority charge carriers in n-type semiconductor are negative electrons while holes, being positive electric charges, act as majority charge carries in p-type material.

Consider a semiconductor diode containing both p-type and n-type regions with a p-n junction between them. To obtain large current through the junction both regions are biased in forward direction that is the positive terminal of the battery is connected to p- region and the negative terminal is connected with n-region.

Transistors like vacuum triodes are utilized for amplifying signals but they perform many other functions as well. There are two main types of transistors differing in their manufacturing technology. The first type is junction or bipolar transistor which may be of p-n-p or n-p-n type. It consists of three parts: the emitter, the base and the collector. To produce current conduction the emitter should be biased in forward direction and the collector should be biased in reverse direction. That is, in p-n-p transistor, for example, the positive voltage is applied to the emitter but the collector requires the negative voltage. Such connection provides the movement of holes from the emitter through the base to the collector. The base controls the motion of current in the transistor.

Another kind of transistor, field-effect transistor (FET), has some advantages over bipolar one. It has higher power gain and no noise. Current in FETs flows through the channel from the source to the drain. The controlling element is the gate. There are some kinds of FFTs and the most popular of them is MOSFET which means metal-oxide-semiconductor FET. MOSFETs have the greatest density of elements and are utilized in microelectronics.

Упражнение III. Ответьте на вопросы.

1. What elements do semiconductor devices consist of?

2. What materials are used for making semiconductor devices?

3. What makes germanium and silicon current conductors?

4. What are the two types of semiconductors?

5. What impurity are p-type / n-type semiconductors doped with?

6. What are charge carriers in p-type / n-type semiconductors?

7. What does a semiconductor diode contain?

8. How is large current obtained?

9. What are the two kinds of transistors?

10. What parts does a transistor comprise?

11. When is current conducted in a transistor?

12. Which voltage is applied to the emitter / collector in a p-n-p transistor?

13. What is the function of the base?

14. What parts does a FET consist of?

15. What are the advantages of a FET over a bipolar transistor?