Degenerate semiconductor
Encyclopedia
A degenerate semiconductor is a semiconductor
with such a high level of doping
that the material starts to act more like a metal
than as a semiconductor.
At moderate doping levels the dopant
atoms create individual doping levels that can often be considered as localized states that can donate electron
s or holes
by thermal promotion (or an optical transition) to the conduction
or valence band
s respectively. At high enough impurity concentrations the individual impurity atoms may become close enough neighbors that their doping levels merge into an impurity band and the behavior of such a system ceases to show the typical traits of a semiconductor, e.g. its increase in conductivity with temperature. On the other hand a degenerate semiconductor still has far fewer charge carriers than a true metal so that its behavior is in many ways intermediary between semiconductor and metal.
Many copper chalcogenides
are degenerate p-type semiconductor
s with relatively large numbers of holes in their valence band. An example is the system LaCuOS1-xSex with Mg doping. It is a wide gap p-type degenerate semiconductor. The hole concentration does not change with temperature, a typical trait of degenerate semiconductors.
Another well known example is indium tin oxide
. Because its plasmon frequency is in the IR-range
it is fairly good metallic conductor, but transparent in the visible range of the spectrum.
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...
with such a high level of doping
Doping (semiconductor)
In semiconductor production, doping intentionally introduces impurities into an extremely pure semiconductor for the purpose of modulating its electrical properties. The impurities are dependent upon the type of semiconductor. Lightly and moderately doped semiconductors are referred to as extrinsic...
that the material starts to act more like a 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...
than as a semiconductor.
At moderate doping levels the dopant
Dopant
A dopant, also called a doping agent, is a trace impurity element that is inserted into a substance in order to alter the electrical properties or the optical properties of the substance. In the case of crystalline substances, the atoms of the dopant very commonly take the place of elements that...
atoms create individual doping levels that can often be considered as localized states that can donate electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
s or holes
Electron hole
An electron hole is the conceptual and mathematical opposite of an electron, useful in the study of physics, chemistry, and electrical engineering. The concept describes the lack of an electron at a position where one could exist in an atom or atomic lattice...
by thermal promotion (or an optical transition) to the conduction
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...
or 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....
s respectively. At high enough impurity concentrations the individual impurity atoms may become close enough neighbors that their doping levels merge into an impurity band and the behavior of such a system ceases to show the typical traits of a semiconductor, e.g. its increase in conductivity with temperature. On the other hand a degenerate semiconductor still has far fewer charge carriers than a true metal so that its behavior is in many ways intermediary between semiconductor and metal.
Many copper chalcogenides
Copper sulfide
Copper sulfides describe a family of chemical compounds and minerals with the formula CuxSy. Both minerals and synthetic materials comprise these compounds. Some copper sulfides are economically important ores....
are degenerate p-type semiconductor
P-type semiconductor
A P-type semiconductor is obtained by carrying out a process of doping: that is, adding a certain type of atoms to the semiconductor in order to increase the number of free charge carriers ....
s with relatively large numbers of holes in their valence band. An example is the system LaCuOS1-xSex with Mg doping. It is a wide gap p-type degenerate semiconductor. The hole concentration does not change with temperature, a typical trait of degenerate semiconductors.
Another well known example is indium tin oxide
Indium tin oxide
Indium tin oxide is a solid solution of indium oxide and tin oxide , typically 90% In2O3, 10% SnO2 by weight. It is transparent and colorless in thin layers while in bulk form it is yellowish to grey...
. Because its plasmon frequency is in the IR-range
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
it is fairly good metallic conductor, but transparent in the visible range of the spectrum.