puolijohteen

Puolijohde is a solid-state material whose electrical conductivity lies between that of a conductor and an insulator. In Finnish scientific usage, puolijohde refers to materials whose charge transport can be controlled by temperature, impurities, light, or electric fields. The most widely used semiconductors are silicon and germanium, with silicon dominating modern electronics.

The electrical behavior arises from electronic band structure. At room temperature, intrinsic carriers are few, and conductivity is enhanced by doping with impurities that donate or accept electrons. N-type materials have extra electrons; P-type have holes. The interface of p-type and n-type regions forms a pn junction, which enables diodes and transistor action.

Common materials include elemental semiconductors like silicon (Si) and germanium (Ge), and compound semiconductors such as gallium arsenide (GaAs), gallium nitride (GaN), and silicon carbide (SiC). Device architectures include diodes, transistors (bipolar and field-effect), and more complex integrated circuits.

Fabrication involves crystal growth (Czochralski or float-zone methods to produce wafers), diffusion or ion implantation for doping, and thin-film deposition and lithography to define patterns. Processing steps must control defects, impurities, and surface quality.

The development of semiconductor-based devices in the mid-20th century enabled modern electronics, computing, and renewable energy technologies. Ongoing research focuses on higher mobility materials, wide-bandgap semiconductors for power electronics, and improvements in silicon-based manufacturing.