What leads to increased mobility of electrons in a semiconductor under light exposure?

Increased mobility of electrons in a semiconductor when exposed to light is primarily due to the absorption of higher energy optical photons. When a semiconductor absorbs photons with sufficient energy, these photons can excite electrons from the valence band to the conduction band. This transition not only leaves behind holes in the valence band but also contributes to the generation of free charge carriers in the conduction band, which can move more freely through the material.

As the electrons gain energy from these photons, their mobility increases because they can overcome the potential barriers within the semiconductor more effectively. This enhanced mobility is key in applications such as photodetectors and solar cells, where efficient charge transport is crucial for performance.

While higher temperature and increased doping levels can also influence electron mobility, the mechanism they employ is different. Higher temperatures can lead to increased lattice vibrations, which might scatter electrons and reduce mobility, and although doping increases the number of free charge carriers, it does not necessarily enhance the mobility itself as effectively as higher energy optical photons do under light exposure.