Puolijohteet

Puolijohteet, also known as semiconductors, are materials whose electrical conductivity lies between that of conductors and insulators. Their conductivity can be precisely controlled through doping, temperature, or electric fields, making them essential for modern electronic devices. Typical examples include silicon, germanium, gallium arsenide, and various compound semiconductors such as gallium nitride.

The unique electrical characteristics of puolijohteet arise from their crystalline crystal structure and the presence of a bandgap between the valence and conduction bands. In a pure semiconductor at absolute zero, no electrons occupy the conduction band, whereas at higher temperatures or with suitable doping, electrons can be promoted across the bandgap. This allows for controlled charge carrier densities and enables the formation of junctions with distinct electronic properties.

Fabrication of puolijohteet devices involves processes such as dicing, doping via diffusion or ion implantation, epitaxial growth, and the deposition of metal contacts. Modern photolithography and cleanroom environments ensure nanoscale precision, enabling the mass production of integrated circuits, diodes, transistors, and solar cells. Doping with donor or acceptor impurities introduces extra electrons or holes, creating n-type or p-type regions that form the basis of p‑n junctions.

Puolijohteet are foundational to the electronics, telecommunications, and renewable‑energy sectors. They power microprocessors, memory chips, power electronics, sensors, and photovoltaic panels. In addition, heterogeneous integration of different semiconductor materials expands functionality, such as high‑frequency communication chips and energy‑efficient lighting.

The global semiconductor market continues to grow, driven by demand for high-performance computing, artificial intelligence, electric vehicles, and the Internet of Things. Research focuses on new materials, such as two‑dimensional semiconductors, and on scaling fabrication techniques to maintain performance while reducing cost.