Semiconductor
lastmod 2018-08-17created 2016-05-141 edits
A semiconductor is a solid material whose conductivity can be changed sharply by energy such as heat. It is usually made by adding impurities to silicon crystals. It is mainly used to make the integrated circuits that make up amplifiers, computing devices, and so on.
A semiconductor behaves like an insulator at very low temperatures and like a conductor at room temperature. However, a semiconductor differs from an insulator when it behaves like an insulator, and from a conductor when it behaves like a conductor. It differs from an insulator in that, unlike an insulator whose band gap is so large that electrons cannot easily rise into the conduction band, its energy band gap is small enough that electrons can easily rise into the conduction band at room temperature. It differs from a conductor in that, at absolute zero, its uppermost electron band is completely filled rather than only partially filled as in a conductor.