Техническое чтение для энергетиков. Бухарова Г.П. - 46 стр.

UptoLike

ВУЗ: 

УлГТУ | Ульяновск

Составители: 

Рубрика: 

48
serves to inject electrons into the p-region.
SEMICONDUCTOR PRINCIPLE
The term "semiconductor" implies a definition, namely, that it is a material
having an electrical conductivity inter mediate between that of metals and insulators.
For many purposes this is a satisfactory definition. We recognize, how ever, that an
enormous range of conductivities can meet this requirement. At room temperature,
the conductivities characteristic of metals are of the order of 104 to 106 ohm־1 cm־1,
while those of insulators may range from 10־22 to 10־10. The materials classed as
semiconductors generally have conductivities from about 10־9 to 103. '
Materials which fall in this conductivity range, but which are largely ionic
conductors, will not be of interest to us; it is electronic conduction with which we
shall be concerned. Some materials show conductivities which approach those of
certain metals, and yet their conduction process is found to be like that of other
semiconductors. Insulators may, under certain conditions, show conduction behavior
which is characteristic of semiconduction. Another criterion commonly associated
with semiconduction is a negative temperature coefficient of resistance.
Semiconductors depend in many cases on crystal imperfections for their unique
properties. These may be foreign atoms incorporated into the crystal lattice, small
deviations from stoichiometry, or lattice defects. As might be expected from the wide
range in conductivities encountered, a large number of materials can be considered as
semiconductors. Among the most investigated, and best understood, of these, are
germanium and silicon among the elements, and indium antimonide, zinc oxide, and
cadmium sulphide among the compounds.
Semiconductors are of practical importance in a number of connections. Their
most direct uses, of course, take advantage of their unique electrical behavior, as in
transistors, crystal rectifiers, and thermisters. Closely related to these are the
applications which combine electrical and optical effects, as in luminescent materials
and photocon-ductors. Furthermore, semiconductors are used in many other ways, in
which any connection between their semiconducting behavior and the particular
application is much more subtle. An example of this, of particular interest to is that of
the oxide catalysts.
ELECTRONS AND HOLES
In many semiconductors it is of great importance to recognize two kinds of
carriers of electrical current: electrons and holes. While the latter, in the final
analysis, represent motion of electrons also, the separation of the two basic
conduction processes is clear. The concept involved will be illustrated in terms of
chemical bonds, by reference to the elements of Group IV although they are quite
general for solids.

Страницы