A semiconductor is a material that has a resistivity between that of a conductor and an insulator. There are many jobs related to this field because semiconductor devices include the transistor, many kinds of diodes including the light-emitting diode, the silicon controlled rectifier, and digital and analog integrated circuits. In a metallic conductor, current is carried by the flow of electrons. In semiconductors, current can be carried either by the flow of electrons (n-type semiconductor) or by the flow of positively-charged holes in the electron structure of the material (p-type). A pure semiconductor is anintrinsic semiconductor. The conductivity of an intrinsic semiconductor material can changed by adding impurities in a process called doping.Semiconductor devices have replaced thermionic devices (vacuum tubes) in most applications. Semiconductor devices are manufactured both as single discrete devices and as integrated circuits (ICs), which consist of a number—from a few to millions—of devices manufactured and interconnected on a single semiconductor substrate.
There are many career opportunities in designing and manufacturing diodes, which are formed by joining n-type and p-type semiconductors. The junction rectifies alternating current, detects light in photodetectors, and generates light in LEDs. Bipolar (holes and electrons) junction transistors (BJTs) are formed from two p-n junctions and are used for amplification and switching. Another type of transistor, the field-effect transistor (electrons only) (FET) operates on the principle that semiconductor conductivity can be increased or decreased by the presence of an electric field. The field may be applied by a p-n junction, forming a junction field-effect transistor (JFET), or by an electrode isolated from the bulk material by an oxide layer. The latter, a metal-oxide-semiconductor field-effect transistor (MOSFET), is the most used semiconductor device today. A charge-coupled device (CCD), microprocessor, random access memory, and read-only memory are examples of multi-terminal semiconductor devices.