An element or compound having an electrical conductivity intermediate between that of conductors and nonconductors (insulators). Most metals have quite high conductivity, while substances like diamond and mica have very low conductivity (high resistance). Between these extremes lie the semiconductors, of which germanium, silicon, silicon carbide, and selenium are examples, with resistivities in the range of 10−2—109 ohms/cm. Slight traces of impurities in the crystalline structure are essential for semiconduction; arsenic is a typical impurity in semiconductor crystals. These impurities function as electron donors or acceptors, and the semiconductor is designated n-type or p-type, depending on the electrical nature of the “holes” or energy deficits in the crystalline lattice.The functioning of semiconductors involves the science of solid-state physics. Their discovery in the early 1940s made possible the development of transistors, with their manifold applications in electronic devices in which they have largely replaced the vacuum tube.There are a few organic semiconducting compounds that contain a significant amount of carbon-carbon bonding and are also capable of supporting electronic conduction. Anthracene and Ziegler-catalyzed acetylene polymers (conjugated polyolefins) are examples.See crystals; Impurity; Solid; Solid-state Chemistry.
