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The Fermi level does not necessarily correspond to an actual energy level (in an insulator the Fermi level lies in the band gap), nor does it require the existence of a band structure. Nonetheless, the Fermi level is a precisely defined thermodynamic quantity, and differences in Fermi level can be measured simply with a voltmeter.
According to a more specific definition presented by Trasatti, [2] the absolute electrode potential is the difference in electronic energy between a point inside the metal (Fermi level) of an electrode and a point outside the electrolyte in which the electrode is submerged (an electron at rest in vacuum).
The Fermi level is set by the device's electrodes. For a device at equilibrium, the Fermi level is a constant and thus will be shown in the band diagram as a flat line. Out of equilibrium (e.g., when voltage differences are applied), the Fermi level will not be flat.
Energy level diagrams for thermionic diode in forward bias configuration, used to extract all hot electrons coming out from the emitter's surface. The barrier is the vacuum near emitter surface. In order to move from the hot emitter to the vacuum, an electron's energy must exceed the emitter Fermi level by an amount
When the two isolated materials are put into intimate contact, the equalization of the Fermi levels brings to the movement of charge from one material to the other, [clarification needed] depending on the values of the work functions. This leads to the creation of an energy barrier, since at the interface between the materials some charge get ...
The Fermi energy is only defined at absolute zero, while the Fermi level is defined for any temperature. The Fermi energy is an energy difference (usually corresponding to a kinetic energy), whereas the Fermi level is a total energy level including kinetic energy and potential energy.
Conduction band edge E C and Fermi level E F determine the electron density in the 2DEG. Quantized levels form in the triangular well (yellow region) and optimally only one of them lies below E F. Heterostructure corresponding to the band edge diagram above. Most 2DEGs are found in transistor-like structures made from semiconductors.
The crossover from hole-dominated conduction (positive ) to electron-dominated conduction (negative ) happens for Fermi levels in the middle of the 1.1 eV-wide gap. In extrinsic (doped) semiconductors either the conduction or valence band will dominate transport, and so one of the numbers above will give the measured values.