valenceband

The valence band is the highest range of electronic states that are normally occupied by electrons in a crystalline solid. At zero temperature, valence bands are typically filled, and they are separated from higher-energy conduction bands by a band gap in insulators and many semiconductors. In metals, the valence band may overlap with the conduction band or be partially filled, so there is no insulating gap and electrons can move under an applied field.

Valence bands arise from the atomic valence orbitals of constituent atoms and become broadened into bands by crystal field interactions and electron hopping. The band structure reflects the bonding and symmetry of the crystal, and in many semiconductors the valence band has substantial p-character.

Conduction in a semiconductor or insulator involves promotion of electrons from the valence band to the conduction band. The absence of an electron in the valence band acts as a positively charged carrier, called a hole. Doping with acceptors creates states near the valence-band edge that enhance p-type conduction; donors create states near the conduction-band edge that favor n-type conduction.

Spin–orbit coupling often splits the valence band into subbands, typically a heavy-hole band, a light-hole band, and a split-off band. At the zone center, the heavy and light hole bands are often degenerate without strain, while the split-off band lies at a higher energy. The effective masses and curvature of these bands determine hole transport and optical transitions.

Understanding the valence band is essential for predicting p-type conductivity, optical absorption, and the behavior of semiconductor heterostructures. Band calculations, including k·p and tight-binding methods, describe the band edges and density of states and are used to model carriers in materials such as silicon, germanium, GaAs, and related compounds.