What happens when light hits silicon?

• A. Silicon conducts heat
• B. Silicon becomes transparent
• C. Silicon is ionized
• D. Silicon's electrons migrate

Answer: (C)

When light shines on silicon, photons transfer their energy to the electrons. If a photon has enough energy to overcome the binding energy of an electron in silicon, that electron can be knocked out of the atom. This leaves the silicon atom as a positively charged ion and produces a free electron—process known as ionization. In typical solid-state contexts, visible light often promotes electrons from the valence band to the conduction band, creating electron‑hole pairs and increasing conductivity, but with sufficiently energetic light (like UV), atoms can indeed be ionized. The other options don’t describe this energy-driven removal of electrons: heat conduction describes thermal energy transfer, transparency would require light to pass through without absorption, and “electrons migrate” is too vague without specifying the energy-driven ejection that ionization implies.