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Also shown: Fermi level E F, valence band edge E V, work function W. In a semiconductor, the work function is sensitive to the doping level at the surface of the semiconductor. Since the doping near the surface can also be controlled by electric fields, the work function of a semiconductor is also sensitive to the electric field in the vacuum.
A semiconductor is a material that is between the conductor and insulator in ability to conduct ... which can move around the lattice and function as a charge carrier
At the junction of a semiconductor and metal, the bands of the semiconductor are pinned to the metal's Fermi level. At the junction of a conductor and vacuum, the vacuum level (from vacuum electrostatic potential) is set by the material's work function and Fermi level. This also (usually) applies for the junction of a conductor to an insulator.
This happens both when the semiconductor is n-type and its work function is smaller than the work function of the metal, and when the semiconductor is p-type and the opposite relation between work functions holds. [3] At the basis of the description of the Schottky barrier formation through the band diagram formalism, there are three main ...
The source of this vacuum potential variation is the variation in work function between the different conducting materials exposed to vacuum. Just outside a conductor, the electrostatic potential depends sensitively on the material, as well as which surface is selected (its crystal orientation, contamination, and other details).
Shown is the graphical definition of the Schottky barrier height, Φ B, for an n-type semiconductor as the difference between the interfacial conduction band edge E C and Fermi level E F. Whether a given metal-semiconductor junction is an ohmic contact or a Schottky barrier depends on the Schottky barrier height, Φ B, of the junction.
The minimum amount of energy needed for an electron to leave a surface is called the work function. The work function is characteristic of the material and for most metals is on the order of several electronvolts (eV). Thermionic currents can be increased by decreasing the work function.
While the work function of a semiconductor can be changed by doping, the electron affinity ideally does not change with doping and so it is closer to being a material constant. However, like work function the electron affinity does depend on the surface termination (crystal face, surface chemistry, etc.) and is strictly a surface property.