Semiconductor

A semiconductor is a material whose electrical conductivity lies between that of a conductor and an insulator. Its conductivity can be controlled by temperature, light, electric fields, and by adding small amounts of impurities, a process known as doping. The electronic behavior of semiconductors is governed by their band structure, including a band gap that determines how easily electrons can be excited to conduct current.

The most widely used semiconductors are silicon and germanium, with silicon dominating modern integrated circuits. Compound semiconductors such as gallium arsenide and silicon carbide provide higher speed or power handling in specific applications. Doping introduces impurities that create either extra electrons (n-type) or holes (p-type). A p-n junction, formed by adjoining p-type and n-type regions, is the basic building block for diodes and transistors. Transistors act as switches or amplifiers, and the metal-oxide-semiconductor field-effect transistor (MOSFET) is the core element of most contemporary digital logic. Complementary MOS (CMOS) circuits pair p- and n-type MOS transistors to reduce power consumption.

Fabrication of semiconductor devices involves crystal growth to create silicon wafers, followed by photolithography, diffusion or ion implantation to dope regions, epitaxial or chemical deposition to build layers, and various etching and metrology steps. High-purity environments and stringent process control are essential to minimize defects.

Applications span integrated circuits, diodes, solar cells, light-emitting diodes, sensors, and power electronics. Research continues into new materials (such as two-dimensional materials and perovskites), novel device architectures, and quantum technologies, with aims including higher performance, reduced energy use, and new functionalities.