The electrical conductivity of a semiconductor increases when electromagnetic radiation of wavelength shorter than a certain threshold (around 2480 nm) is incident on it. This happens because the photon energy from the radiation is sufficient to excite electrons from the valence band to the conduction band, reducing the band gap. For wavelength shorter than this threshold, the photon energy is at least equal to the band gap energy, thus generating electron-hole pairs that increase conductivity. In summary, the key condition is:
- The electrical conductivity increases when electromagnetic radiation with wavelength shorter than approximately 2480 nm (which corresponds to photon energy equal to or greater than the band gap energy) hits the semiconductor.
