Materialbandgap

In solid-state physics, the material bandgap, or band gap, is the energy range in a solid where no electron states can exist. It is the difference between the top of the valence band and the bottom of the conduction band. Materials with a large bandgap are insulators at room temperature, while those with a smaller gap are semiconductors; metals have overlapping bands and effectively no gap.

Direct versus indirect bandgaps: In a direct bandgap material, the conduction-band minimum and valence-band maximum occur at the same crystal momentum, allowing electrons to emit or absorb photons efficiently. Indirect bandgap materials require a phonon to conserve momentum, making radiative processes less efficient; this distinction influences applications such as LEDs and solar cells.

Measurement and theory: The bandgap is usually expressed in electronvolts (eV). It can be measured by optical absorption, photoluminescence, or electrical methods, and can be predicted by electronic structure calculations. Temperature tends to reduce the bandgap, a behavior described by empirical models such as the Varshni equation.

Engineering and materials: The bandgap depends on composition and structure. Alloying, quantum confinement in nanostructures, and strain can tune the gap. Common examples include silicon (~1.1 eV, indirect), GaAs (~1.42 eV, direct), GaN (~3.4 eV), and SiC (~3.0–3.3 eV).

Applications: Bandgap determines optical absorption and emission, carrier transport, and device operation in electronics and photonics, including transistors, diodes, LEDs, laser diodes, and solar cells. Understanding and controlling the bandgap is central to material design for energy and information technologies.