Текст Semiconductors
SEMICONDUCTOR PRINCIPLE
The term «semiconductor» implies a definition, namely, that it is a material having an electrical conductivity intermediate between that of metals and insulators.
For many purposes this is a satisfactory definition. However, 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.
Some materials show conductivities, 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 thermistors. Closely related to these are the applications which combine electrical and optical effects, as in luminescent materials and photoconductors. 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.