Semiconductors and semiconductor materials are used to fabricate microelectronic devices and optoelectronic devices such as transistors, photodetectors and solar cells. Silicon (Si) is the most commonly used semiconductor material today; however, other semiconductor material types are also available. The number of valence shell electrons in a semiconductor material places this category of material between insulators (poor electrical conductors) and metals (good semiconductors). Insulators have a filled valence shell (eight electrons) and a large band gap, which results in poor electrical conductivity. Metals have a partially-filled valence shell and overlapping band gap, which results in free-traveling electrons and high electrical conductivity. Semiconductors and semiconductor materials are useful because their electrical conductivity can be altered with dopants, an applied electric field, or electromagnetic radiation.
There are two basic categories of semiconductors and semiconductor materials: electrical semiconductors and compound semiconductors. Silicon (Si) and germanium (Ge), the most common electrical semiconductors, are used in many semiconductor components. Gallium arsenide (GaAs) and indium phosphide (InP) are examples of composite semiconductors that contain added materials or dopants. Semiconductor doping, the addition of a very small amount of a foreign substance to a pure semiconductor crystal, provides a semiconductor with an excess of conducting electrons or an excess of conducting holes. The first semiconductors and semiconductor materials produced electrical conduction through contact with a metal wire. Subsequent technologies used semiconductor crystals and semiconductor diodes. A semiconductor diode allows current to flow in one direction only.
There are many applications for semiconductors and semiconductor materials in materials engineering, such as the fabrication of transistors, photodetectors and solar cells. Major semiconductor manufacturers and providers of semiconductors and semiconductor materials include Lattice Semiconductor Corporation, Xilinx, Altera, Actel and Quicklogic. Other semiconductor manufactures are located across the United States and around the world. In semiconductor manufacturing, transistors are placed together to create a silicon chip. The semiconductor manufacturer than creates a microprocessor from the silicon chip.