Pooljuhtes

Pooljuhtes are a class of materials whose electrical conductivity lies between that of metals and insulators. The conductivity of pooljuhtes is highly sensitive to temperature, impurities (dopants) and applied electric fields. The most widely used pooljuht material is crystalline silicon, but germanium and numerous compound semiconductors such as gallium arsenide (GaAs), gallium nitride (GaN) and silicon carbide (SiC) are also important for specific applications. The behavior of pooljuhtes is commonly explained with band theory, where electrons inhabit a valence band and a higher-energy conduction band separated by a band gap.

Doping introduces impurities that donate free carriers: donors create n-type semiconductors with excess electrons, while acceptors create p-type semiconductors with holes as majority carriers. When p-type and n-type materials are joined, a p–n junction forms, enabling diodes that conduct preferentially in one direction and exhibit rectifying behavior. The control of carrier concentration and mobility in pooljuhtes underpins most electronic devices, including transistors, diodes and integrated circuits.

Common devices and applications include diodes, bipolar and field-effect transistors, and increasingly complex integrated circuits that power modern computers and smartphones. Semiconductors also enable solar cells, light-emitting diodes (LEDs), photodetectors and various sensors. Manufacturing involves crystal growth (for example Czochralski or float-zone methods) to produce wafers, followed by lithography, etching, deposition and precise doping to create intricate device structures.

Historically, the invention of the transistor in 1947 and the development of integrated circuits in the late 1950s revolutionized electronics and information technology. Today pooljuhtes remain essential to technology, with ongoing research into new materials, higher mobility, wider bandgaps and flexible or transparent electronics, aimed at improving performance and energy efficiency.