Puolijohdeilmiöt

Puolijohdeilmiöt refers to the unique electrical properties exhibited by semiconductor materials. Unlike conductors, which allow electricity to flow freely, or insulators, which strongly resist it, semiconductors possess conductivity that falls between these two extremes. This conductivity can be significantly altered by external factors such as temperature, light, and the presence of impurities.

The fundamental behavior of semiconductors is governed by their electronic band structure. In a semiconductor, the valence band, where electrons are normally bound to atoms, is separated from the conduction band, where electrons can move freely to conduct electricity, by a small energy gap. At absolute zero temperature, a pure semiconductor acts like an insulator. However, as temperature increases, some electrons gain enough thermal energy to jump across the band gap into the conduction band, increasing conductivity.

The introduction of impurities, a process called doping, is crucial for controlling semiconductor properties. Doping with elements that have more valence electrons than the semiconductor material (n-type doping) introduces excess free electrons into the conduction band. Doping with elements that have fewer valence electrons (p-type doping) creates "holes," which are essentially vacancies where electrons could be, and these holes can also carry charge. The junction formed between n-type and p-type semiconductor materials, known as a p-n junction, is the basis for many electronic devices, including diodes and transistors, enabling the control and amplification of electrical signals. These phenomena are the cornerstone of modern electronics.