Puolijohteella

Puolijohteella, or semiconductor in English, refers to a material that has electrical conductivity between that of a conductor and an insulator. This property makes semiconductors crucial components in modern electronics. Their conductivity can be manipulated by introducing impurities, a process called doping, which can either increase or decrease the number of free charge carriers (electrons or holes).

The most commonly used semiconductors are silicon (Si) and germanium (Ge), both from Group 14 of the periodic table. However, compounds like gallium arsenide (GaAs) and cadmium telluride (CdTe) are also widely employed for specific applications. The behavior of charge carriers in semiconductors is governed by quantum mechanics, particularly the concept of energy bands. The valence band is where electrons are bound to atoms, while the conduction band is where they are free to move. The gap between these bands, known as the band gap, determines the material's conductivity.

At absolute zero temperature, a pure semiconductor acts as an insulator. As temperature increases, thermal energy excites electrons from the valence band to the conduction band, creating free electrons and holes, thus increasing conductivity. Doping creates extrinsic semiconductors, either n-type (excess electrons) or p-type (excess holes), which are the foundation for devices like diodes, transistors, and integrated circuits. These devices are responsible for controlling, amplifying, and switching electrical signals, enabling the functionality of virtually all electronic devices.