Transistors and Semiconductor Devices

Text A

LESSON TWO

I. Study text A. Try to understand all details. Use a dictionary if necessary:

1. Devices consisting of solid pieces of crystalline material which allowed alternating current to flow more readily in one direction than the other were known long before the invention of the thermionic valve. The crystal set¹ which became so well known in the early days of radio depended on the rectifying action at the point of contact between the surface of certain crystals and a fine wire. Crystal valves², using silicon crystals, were found to be more efficient for the very high frequency signals reaching radar receivers than any thermionic valves. The action of these devices was not understood, but they were all made from materials which we now classify as semiconductors: substances which let electric current pass through them more easily than insulators do but much less easily than do true conductors. These semiconductor devices were used as rectifiers although by 1924 a scientific worker at the laboratory headed by Bonch-Bruyevich in Nizhni Novgorod Oleg Losev for the first time in the history of electronics had achieved amplification using a semiconductor crystal. Unfortunately, Losev's discovery did not receive due attention.

2. In 1948 Bardeen and Brattain invented the point-contact transistor and Shockley invented the junction transistor shortly after. The transistor is a semiconductor triode possessing characteristics which are similar in many respects to those of thermionic triodes. At present transistors are widely used in amplifiers, receivers, transmitters, oscillators, TV sets, measuring instruments, pulse circuits, computers, and many other types of radio equipment.

3.The invention of transistors and solid-state devices led to an acceleration in the growth of electronics. Why were these new devices so important and why are they steadily replacing their older equivalents? A brief review of their advantages compared with thermionic devices will provide the answers to these questions. Transistors are made from parts which do not wear out. Transistors waste very little power. They require no heating to generate their free electrons. This means that equipment made with transistors is more efficient, lighter than comparable valve equipment.

4. Since no heating is required there is no delay in transistor equipment waiting for things to warm up, as there is with thermionic valves. This is a great advantage with 'entertainment' equipment, such as radio and television receivers, and it may be vital with some kinds of measuring or recording equipment.

5. Their very small size and weight, combined with low heat dissipation³, permits very high density packing of components and, in combination with their reliability, this has made possible the design of the very compact circuits which are essential for such applications as computers, portable measuring instruments, satellite instrumentation, etc.

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