http://t.co/hgbABOxUlm by @ulaulaman about #nobelprize2014 on #physics #led #light #semiconductors
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One of the first classifications that you learn when you start to study the behavior of matter interacting with electricity is between conductors and insulators: a conductor is a material that easily allows the passage of electric charges; on the other hand, an insulator prevents it (or makes it difficult). It is possible to characterize these two kinds of materials through the physical characteristics of the atoms that compose them. Indeed, we know that an atom is characterized by having a positive nucleus with electron clouds which rotate around it: to characterize a material is precisely the behavior of the outer electrons, those of the external band. On the other hand, the energy bands of every atom are characterized by specific properties: there are the valence bands, where the electrons are used in the chemical bonds, and the conduction bands, where the electrons are free to move, the "mavericks" of the atom, used for ionic bonds. At this point I hope it is simple to characterize a conductive material such as the one whose atoms have electrons both in the valence band, both in the conduction band, while an insulating material is characterized by having full only the valence band.
Now, in band theory, the probability that an electron occupies a given band is calculated using the Fermi-Dirac distribution: this means that there is a non-zero probability that an insulator's electron in the valence band is promoted to the conduction band, but it is extremely low because of the large energy difference between the two levels. Moreover, there is an energy level said Fermi level that, while in the conductors is located within the conduction band, in the insulation is located between the two bands, the conduction and valence, allowing a valence electron to jump more easily in the conduction band.
