How do electron-hole pairs form in semiconductors?

Electron-hole pairs in semiconductors are created when energy is supplied to the material, enabling electrons to gain enough energy to break free from their atomic bonds. When a photon of sunlight strikes the semiconductor, it can transfer its energy to an electron. If the energy of the photon is sufficient to overcome the bandgap of the semiconductor, it can dislodge the electron from its valence band, creating an electron in the conduction band and leaving behind a vacancy, or "hole," in the valence band. This process is fundamental to the operation of devices such as solar cells, where sunlight is converted directly into electrical energy by generating these pairs.

While thermal agitation refers to the random motion of atoms and can also contribute to the formation of electron-hole pairs by providing thermal energy, it is typically less efficient compared to the more direct mechanism provided by photons in relevant contexts such as photovoltaics. Applying voltage can influence the behavior and separation of existing electron-hole pairs but does not directly create them. During cooling, the likelihood of forming electron-hole pairs generally decreases, as lower thermal energy reduces the number of electrons that can transition to the conduction band.