Semiconductors

Elements in group four of the periodic table (carbon, silicon and germanium) and many metal oxides are semiconductors. They have conductivities that are intermediate between metals and dielectrics (insulators).

Natural semiconductors were neglected in favor of intensive studies of superconductivity in the years from 1900 to 1945 because it was found that the conductivity of the semiconducting materials varied in unpredictable ways from sample to sample.

When it became possible to grow very pure crystalline samples it became evident that very low levels of impurities (too small to measured at the time) were responsible for the unpredictable behavior.

Conductivity in semiconductors depends on the availability of charge carriers (negative electrons or positive holes). The electron/hole density in silicon and germanium is influenced by the presence, in minute quantities, of impurities from groups 3 and 5 of the periodic table. Specially prepared semiconductor materials are said to be doped with these elements.

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