• Semiconductors are substances in which the electric current formed by the movement of electrons, and the magnitude of the resistivity is between conductors and insulators. Semiconductors are chemical elements of IV and VI groups of the periodic system D. I. Mendeleev, graphite, silicon, germanium, selenium, and others, as well as many oxides and other compounds of various metals. The number of mobile charge carriers in semiconductors under normal conditions is small, but it increases hundreds and thousands of times when some external influences (heat, light etc D.), as well as the presence in the semiconductor of certain impurities.
Semiconductors are divided into electronic (n type) and hole (p type). In the n - type semiconductor as the charge carriers are considered electrons, which in the formation of the current move across the semiconductor, like the free electrons in metals. In the p type semiconductor as the charge carriers are considered so-called holes (under the holes is understood as free place the atom that can be occupied by outsiders to it by the electron). Holes are considered equivalent to a positive charge equal to the electron. In the formation of the current in the semiconductor of type p, the electrons make only to jumps between neighboring atoms; in the jump of an electron from one hole to another hole moves in the opposite direction, that is regarded as a education current.