How are electron-hole pairs generated in semiconductors?

In semiconductors, electron-hole pairs are generated primarily when electrons gain sufficient energy to move from the valence band to the conduction band. This transition creates a free electron that can conduct electricity and leaves behind a vacancy, known as a hole, in the valence band.

When an electron is excited into the conduction band, it not only becomes free to move, facilitating electrical conductivity, but the absence of that electron in the valence band creates a hole. These hole can also participate in conduction by allowing adjacent electrons to fill the vacancy, effectively allowing charge to flow through the material.

The process of generating electron-hole pairs can occur via different mechanisms, such as through the absorption of light (photons) or the introduction of thermal energy. However, the most direct and fundamental explanation presented is the movement of electrons to the conduction band, which inherently creates those necessary electron-hole pairs. This mechanism is critical in understanding the behavior of semiconductors in various applications, like diodes and transistors, where the control of electron-hole generation is essential.