In semiconductors, the concept of charge carriers refers to the mobile electrically charged particles that can carry electric current through the material. These charge carriers are responsible for the conductivity of semiconductors and play a crucial role in the operation of semiconductor devices.
There are two main types of charge carriers in semiconductors:
Electrons: Intrinsic semiconductors, such as pure silicon or germanium, have electrons as their primary charge carriers. At absolute zero temperature, these materials have a complete valence band and an empty conduction band, with a band gap separating the two. When energy is supplied to the material (usually through thermal energy or external influences like light), electrons can gain enough energy to move from the valence band to the conduction band, creating free electrons that can move through the crystal lattice, contributing to electric current.
Holes: Holes are another type of charge carrier in semiconductors. A hole is essentially an empty space in the valence band where an electron has left. When an electron leaves its position in the valence band to move to the conduction band, it leaves behind a positively charged hole. This hole can behave as a mobile particle and move through the material, effectively carrying a positive charge. Holes are especially important in the context of p-type semiconductors, which are doped (intentionally contaminated) with certain atoms to create excess holes in the valence band.
The behavior of charge carriers in semiconductors is crucial for understanding the operation of various semiconductor devices, such as diodes, transistors, and integrated circuits. By manipulating the concentration and mobility of charge carriers through doping and other techniques, engineers can design and control the performance of these devices for specific applications.