A degenerate semiconductor is a

semiconductor A semiconductor is a material with electrical conductivity between that of a conductor and an insulator. Its conductivity can be modified by adding impurities (" doping") to its crystal structure. When two regions with different doping level ...

with such a high level of doping that the material starts to act more like a

metal A metal () is a material that, when polished or fractured, shows a lustrous appearance, and conducts electrical resistivity and conductivity, electricity and thermal conductivity, heat relatively well. These properties are all associated wit ...

than a semiconductor. Unlike non-degenerate semiconductors, these kinds of semiconductor do not obey the

law of mass action In chemistry, the law of mass action is the proposition that the rate of a chemical reaction is directly proportional to the product of the activities or concentrations of the reactants. It explains and predicts behaviors of solutions in dy ...

, which relates intrinsic carrier concentration with temperature and bandgap. At moderate doping levels, the

dopant A dopant (also called a doping agent) is a small amount of a substance added to a material to alter its physical properties, such as electrical or optics, optical properties. The amount of dopant is typically very low compared to the material b ...

atoms create individual doping levels that can often be considered as localized states that can donate

electron The electron (, or in nuclear reactions) is a subatomic particle with a negative one elementary charge, elementary electric charge. It is a fundamental particle that comprises the ordinary matter that makes up the universe, along with up qua ...

s or

holes A hole is an opening in or through a particular medium, usually a solid body. Holes occur through natural and artificial processes, and may be useful for various purposes, or may represent a problem needing to be addressed in many fields of en ...

by thermal promotion (or an optical transition) to the

conduction Conductor or conduction may refer to: Biology and medicine * Bone conduction, the conduction of sound to the inner ear * Conduction aphasia, a language disorder Mathematics * Conductor (ring theory) * Conductor of an abelian variety * Condu ...

valence band In solid-state physics, the valence band and conduction band are the bands closest to the Fermi level, and thus determine the electrical conductivity of the solid. In nonmetals, the valence band is the highest range of electron energies in ...

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 P-type or type P may refer to: P-type * P-type orbit, type of planetary orbit in a binary system * P-type asteroid, type of asteroid * P-type semiconductor * MG P-type, a type of automobile * P-type ATPase, evolutionarily related ion and lipid ...

s with relatively large numbers of holes in their valence band. An example is the system LaCuOS_1−xSe_x 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 (ITO) is a ternary composition of indium, tin and oxygen in varying proportions. Depending on the oxygen content, it can be described as either a ceramic or an alloy. Indium tin oxide is typically encountered as an oxygen-saturate ...

. Because its

plasma frequency Plasma oscillations, also known as Langmuir waves (after Irving Langmuir), are rapid oscillations of the electron density in conducting media such as plasmas or metals in the ultraviolet region. The oscillations can be described as an instability ...

is in the IR-range,{{ cite journal, doi= 10.1021/jp026600x, title= Indium Tin Oxide Plasma Frequency Dependence on Sheet Resistance and Surface Adlayers Determined by Reflectance FTIR Spectroscopy, author1=Scott H. Brewer , author2=Stefan Franzen , journal = J. Phys. Chem. B, volume=106 , issue=50, pages=12986–12992, year=2002 it is a fairly good metallic conductor, but transparent in the visible range of the spectrum.

References

Semiconductor material types Condensed matter physics