![]() above 4 eV), so that all bands below that energy are completely filled, while all higher-lying bands are completely empty, except for some thermal excitation which is negligibly unless at high temperatures. In some cases, the Fermi energy lies somewhere in a large band gap (with a width of e.g. Materials with Different Electronic Structures That is the band gap which is usually meant when the text mentions the band gap of a material. Importantly, there are energy regions for which no electronic states exist.Ī medium can have many of those, but the band gap of central importance is that near the Fermi energy, where the level occupation according to the Fermi function drops substantially. The band gap of central importance is that near the Fermi energy. At a finite temperature (room temperature, for example), the distribution of electrons over the electronic states is described with a Fermi function, which drops with increasing energy.(If one imagines to fill more and more electron into such a system, the electrons will first occupy the very lowest energy levels and then levels with increasingly higher energies, as the lower ones are already occupied.) At very low temperatures, the electrons will occupy the levels with the lowest possible energies.This has profound implications for the population in levels: The application of quantum mechanics in solid-state physics has led to physical models which involve a continuum of states which can be occupied by electrons.Įach state has a certain energy and k vector (crystal momentum).Īs electrons are fermions, each of those states can be occupied by one electron only. There are also so-called photonic band gaps, which are briefly discussed in the last section of this article.īoth types of bandgaps are very relevant in optics and photonics. ![]() This article mainly deals with electronic band gaps (bandgaps), including their importance for the optical absorption and emission properties of materials. How to cite the article suggest additional literature Definition: a range of energies for which there are no states of carriers in a medium
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