What occurs to the conductivity of a photosensitive semiconductor junction when illuminated?

When a photosensitive semiconductor junction is illuminated, it experiences an increase in conductivity due to the generation of charge carriers. In a semiconductor, light can excite electrons from the valence band to the conduction band, creating free charge carriers—electrons and holes. This process effectively lowers the resistance of the semiconductor junction because a greater number of charge carriers enhances its ability to conduct electricity.

As conductivity increases, resistance corresponds to a decrease, leading to a lower junction resistance when exposed to light. This characteristic is fundamental to devices such as photodiodes and solar cells, which rely on the conversion of light energy into electrical energy. The overall behavior underscores the importance of illumination in influencing the electrical properties of semiconductors in various applications.