Holes are

• A. Negative charge carriers in the conduction band
• B. Positive charge carriers representing vacant electron states in the valence band
• C. Free electrons in the conduction band
• D. Photons in the lattice

Answer: (B)

Holes are vacancies in the valence band that behave as positive charge carriers. In a normally filled valence band, removing an electron leaves behind an empty state. That vacancy can be filled by a neighboring electron, and as electrons move to fill holes, the hole itself appears to move in the opposite direction. Because the missing electron carries negative charge, the vacancy carries a net positive charge, so it acts like a mobile positive charge carrier. This is why semiconductors with a lot of holes (p-type) conduct via holes. They are not free electrons in the conduction band, nor photons. The description of holes as vacant electron states in the valence band captures what they really are.