What are the two types of charge carriers in insulators and semiconductors as described?

• A. Free Electron and Hole
• B. Ions and Electrons
• C. Electron and Hole
• D. Photons and Phonons

Answer: (C)

In insulators and semiconductors the flow of electrical charge comes from two kinds of mobile carriers: electrons and holes. An electron in the conduction band moves and carries negative charge when a field is applied. A hole is the absence of an electron in the valence band; as electrons move to fill neighboring vacancies, the missing spot behaves like a positively charged particle that moves in the opposite direction to electrons. This electron–hole pair is what accounts for most conduction in these materials.

Other options mix up what actually carries charge. Ions would imply ionic conduction, which isn’t the primary mechanism in most solids discussed here. Photons and phonons are energy carriers (quanta of light and lattice vibrations), not charge carriers. So the standard, most accurate description is that conduction in insulators and semiconductors involves electrons and holes.