puolijohde

Puolijohde is the Finnish term for semiconductor. A semiconductor is a material whose electrical conductivity lies between that of a conductor and an insulator and can be modulated by impurities (doping), temperature, light, or electric field. Most semiconductors are crystalline solids with a band gap that governs carrier generation.

Materials commonly used include silicon and germanium, with silicon dominating modern electronics. Doping introduces donor or acceptor impurities to create n-type or p-type semiconductors.

A junction between n-type and p-type regions, a pn junction, forms the basic element of diodes and transistors. This junction enables control of current flow and amplification of signals, fundamental to most electronic devices.

Key devices include diodes, transistors (bipolar junction transistors and field-effect transistors), and integrated circuits. Semiconductors enable solar cells, LEDs, sensors, and many microelectronic components.

Manufacture involves producing large, defect-free crystal wafers, typically silicon, grown by the Czochralski or float-zone methods. Doping and diffusion or ion implantation introduce impurities; subsequent steps include layer deposition, lithography, etching, and metallization to create working devices.

Semiconductors have driven rapid advances in computing, telecommunications, and energy technologies. Ongoing research explores wide-bandgap materials such as gallium nitride and silicon carbide for high-power and high-frequency applications, as well as nano-scale and quantum devices.