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Different spectroscopy methods make use of or can measure band bending: Surface photovoltage is a spectroscopy method used to determine the minority carrier diffusion length of semiconductors. The band bending at the surface of a semiconductor results in a depletion region with a surface potential.
Rather, band bending refers to the local changes in electronic structure, in the energy offset of a semiconductor's band structure near a junction, due to space charge effects. The primary principle underlying band bending inside a semiconductor is space charge: a local imbalance in charge neutrality.
An example band-bending diagram is shown in the figure. For convenience, energy is expressed in eV and voltage is expressed in volts, avoiding the need for a factor q for the elementary charge . In the figure, a two-layer structure is shown, consisting of an insulator as left-hand layer and a semiconductor as right-hand layer.
The surfaces of semiconductors are often depletion regions (or space charge regions) where a built-in electric field due to defects has swept out mobile charge carriers. A reduced carrier density means that the electronic energy band of the majority carriers is bent away from the Fermi level. This band-bending gives rise to a surface potential ...
These charge imbalances have electrostatic effects that extend deeply into semiconductors, insulators, and the vacuum (see doping, band bending). Along the same lines, most electronic effects (capacitance, electrical conductance, electric-field screening) involve the physics of electrons passing through surfaces and/or near interfaces.
Semiconductor interfaces can be organized into three types of heterojunctions: straddling gap (type I), staggered gap (type II) or broken gap (type III) as seen in the figure. [9] Away from the junction, the band bending can be computed based on the usual procedure of solving Poisson's equation. Various models exist to predict the band alignment.
In this type of alignment, this means that both of the bands of semiconductor A will bend upwards, whilst both of the bands of semiconductor B will bend downwards. The band bending, caused by the built-in potential, is determined by the interface position of the Fermi level, and predicting or measuring this level is related to the Schottky ...
Shown to the right is a diagram of band-bending interfaces between two different metals (high and low work functions) and two different semiconductors (n-type and p-type). Volker Heine was one of the first to estimate the length of the tail end of metal electron states extending into the semiconductor's energy gap. He calculated the variation ...