How does light create charge carriers in a photoconductor?

In a semiconductor, light creates charge carriers through the process of photoconductivity. Under normal conditions, most electrons in a semiconductor are bound within the valence band, resulting in low electrical conductivity.

When the material is exposed to light, it is bombarded by photons. If these photons possess sufficient energy—specifically, energy equal to or greater than the material's band gap—they can excite electrons from the valence band into the conduction band.12

Once in the conduction band, these electrons become relatively free to move and carry an electric current. Simultaneously, the excitation of an electron leaves behind a vacancy in the valence band known as a "hole." These holes act as mobile positive charge carriers. Consequently, the illumination of the semiconductor increases the concentration of both free electrons and holes, thereby enhancing the material's overall electrical conductivity.1