Band diagram
Encyclopedia
This article refers to the electronic bandgap found in the semiconductors; for discussion of the photonic band gap, see Photonic Crystal
article.
In solid-state physics
of semiconductors, a band diagram is a diagram showing the electron energy of the valence band
and conduction band
edges vs. some spatial dimension, which is often denoted x. Likewise, the Fermi level
is usually indicated in the diagram. Sometimes the intrinsic Fermi energy, Ei, which is the Fermi level in the absence of doping, may be shown also. The work function and electron affinity are shown on some diagrams as well. These diagrams help to explain the operation of many kinds of semiconductor device
s.
Metal
s have unfilled valence band, or greatly overlapping valence and conduction bands. Semimetals have a small overlap between valence and conduction bands, whereas semiconductor
s have a small band gap
between them. The Fermi level is located in the middle of the band gap for an undoped semiconductor. Insulators have a large band gap, so that electrons cannot escape the valence band to enter the conduction band.
Photonic crystal
Photonic crystals are periodic optical nanostructures that are designed to affect the motion of photons in a similar way that periodicity of a semiconductor crystal affects the motion of electrons...
article.
Solid-state physics
Solid-state physics is the study of rigid matter, or solids, through methods such as quantum mechanics, crystallography, electromagnetism, and metallurgy. It is the largest branch of condensed matter physics. Solid-state physics studies how the large-scale properties of solid materials result from...
of semiconductors, a band diagram is a diagram showing the electron energy of the valence band
Valence band
In solids, the valence band is the highest range of electron energies in which electrons are normally present at absolute zero temperature....
and conduction band
Conduction band
In the solid-state physics field of semiconductors and insulators, the conduction band is the range of electron energies, higher than that of the valence band, sufficient to free an electron from binding with its individual atom and allow it to move freely within the atomic lattice of the material...
edges vs. some spatial dimension, which is often denoted x. Likewise, the Fermi level
Fermi level
The Fermi level is a hypothetical level of potential energy for an electron inside a crystalline solid. Occupying such a level would give an electron a potential energy \epsilon equal to its chemical potential \mu as they both appear in the Fermi-Dirac distribution function,which...
is usually indicated in the diagram. Sometimes the intrinsic Fermi energy, Ei, which is the Fermi level in the absence of doping, may be shown also. The work function and electron affinity are shown on some diagrams as well. These diagrams help to explain the operation of many kinds of semiconductor device
Semiconductor device
Semiconductor devices are electronic components that exploit the electronic properties of semiconductor materials, principally silicon, germanium, and gallium arsenide, as well as organic semiconductors. Semiconductor devices have replaced thermionic devices in most applications...
s.
Metal
Metal
A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...
s have unfilled valence band, or greatly overlapping valence and conduction bands. Semimetals have a small overlap between valence and conduction bands, whereas semiconductor
Semiconductor
A semiconductor is a material with electrical conductivity due to electron flow intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter...
s have a small band gap
Band gap
In solid state physics, a band gap, also called an energy gap or bandgap, is an energy range in a solid where no electron states can exist. In graphs of the electronic band structure of solids, the band gap generally refers to the energy difference between the top of the valence band and the...
between them. The Fermi level is located in the middle of the band gap for an undoped semiconductor. Insulators have a large band gap, so that electrons cannot escape the valence band to enter the conduction band.