Energiegap

Energiegap, also known as the energy gap or band gap, is the energy difference between the top of the valence band and the bottom of the conduction band in a solid. In crystalline materials, electron states form bands, and the energiegap corresponds to the range of energies where no electronic states exist. The size of this gap strongly influences a material’s electrical and optical properties: large gaps typically yield insulators, smaller gaps produce semiconductors, and negligible gaps correspond to metals where bands overlap.

There are two main types of band gaps. A direct band gap occurs when the minimum of the conduction band and the maximum of the valence band occur at the same momentum, allowing efficient photon emission and absorption. An indirect band gap requires a change in momentum, usually involving phonons, which makes radiative processes less likely and often affects light-emitting performance.

Measuring and characterizing energiegap can be done through optical absorption, photoluminescence, or photoemission spectroscopy. The onset of absorption or emission provides an estimate of the gap, and methods such as Tauc plots help determine the optical gap from data. Temperature, pressure, and quantum confinement in nanoscale structures can modify the gap: for many semiconductors the gap decreases slightly with temperature, while confinement in nanostructures tends to widen the gap.

Common examples include silicon (~1.12 eV, indirect), gallium arsenide (~1.43 eV, direct), and diamond (~5.5 eV). The energiegap is a central parameter in the design of semiconductors for electronics and optoelectronics, including diodes, transistors, LEDs, and solar cells.