Semiconductor

Semiconductors are materials with electrical conductivities that are intermediate between those of conductorss and insulators. Semiconductors are useful for electronic purposes because they can carry an electric current by electron propagation or hole propagation, and because this current is generally uni-directional and the amount of current may be influenced by an external agent (see diode, transistor, amplifier etc.). Electron propagation is the same sort of current flow seen in a standard copper wire - heavily ionized atoms pass excess electrons down the wire from one atom to another in order to move from a more negatively ionized area to a less negatively ionized area. "Hole" propagation is a rather different proposition - in the case of a semiconductor experiencing hole propagation, the charge moves from a more positively ionized area to a less positively ionized area by the movement of the electron hole created by the absence of an electron in a nearly-full electron shell.

While silicon dioxide or sand is an insulator, pure silicon is a semiconductor.

The properties of semiconductors, e.g. the number of carriers (and therefore the prevalence of electron propagation or hole propagation), can be controlled by "doping" the semiconductor blocks with impurities. A semiconductor with more electrons than holes is called an n-type semiconductor, while a semiconductor with more holes than electrons is called a p-type semiconductor.

Semiconductors are the fundamental materials in many modern electronic devices.