Техническое чтение для энергетиков. Бухарова Г.П. - 50 стр.

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52
SEMICONDUCTORS
The periodic law of elements discovered by Mendelyeev had a number of
important scientific and industrial results, one of them being the discovery of
germanium. Germanium is the semiconductor used in most transistors available at
present.
But what are semiconductors? They include almost all minerals, many chemical
elements, a great variety of chemical compounds, alloys of metals, and a number of
organic compounds. Like metals, they conduct electricity but they do it less
effectively. In metals all electrons are free and in insulators they are fixed. In
semiconductors electrons are fixed, too, but the connection is so weak that the heat
motion of the atoms of a body easily pulls them away and sets them free.
It is not difficult to understand that the term "semiconductor" has been used
because the material in question really occupies a place between the conductors of the
electric current and the non-conductors, that is insulators. The term shows that they
conduct electricity less readily than conductors but much better than insulators.
Minerals and crystals appear to possess some unexpected properties. For
instance, it is well known that their conductivity increases with heating and falls with
cooling.
As a semiconductor is heated, free electrons in it increase in number, hence, its
conductivity increases as well now-ever, heat is by no means the only phenomenon
influencing semiconductors. They are sensitive to light, too. Take germanium as an
example. Its electrical properties may greatly change when it is exposed to light. With
the help of a ray light directed at a semiconductor, we can start or. stop various
machines, effect remote control, and perform lots of other useful things. Just as they
are influenced by falling light, semiconductors are also influenced by all radiation.
Generally speaking, they are so sensitive that a heated object can be detected by its
radiation.
As previously mentioned, such dependence of conductivity on heat and light has
opened up great possibilities for various uses of semiconductors. The semiconductor
devices are applied for transmission of signals, for automatic control of a variety of
processes, for switching on engines, for the reproduction of sound, protection of high-
voltage transmission lines, speeding up of some chemical reactions, and so on. On the
one hand they may be used to transform light and heat energy directly into electric
energy without any complex mechanism with moving parts, and on the other hand,
they are capable of generating heat or cold from electricity.
Soviet engineers and scientists turned their attention to semiconductors more
than thirty years ago. They saw in them a means of solving an old engineering
problem, namely, that of direct conversion of heat into electricity without boilers or
machines. Semiconductor thermocouples created in the USSR convert heat directly
into electricity just as a complex system consisting of a steam boiler, a steam engine
and a generator does it.

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