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 ...

physics Physics is the scientific study of matter, its Elementary particle, fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. "Physical science is that department of knowledge whi ...

, the photo–Dember effect (named after its discoverer ) is the formation of a charge

dipole In physics, a dipole () is an electromagnetic phenomenon which occurs in two ways: * An electric dipole moment, electric dipole deals with the separation of the positive and negative electric charges found in any electromagnetic system. A simple ...

in the vicinity of a

surface after ultra-fast photo-generation of

charge carriers In solid state physics, a charge carrier is a particle or quasiparticle that is free to move, carrying an electric charge, especially the particles that carry electric charges in electrical conductors. Examples are electrons, ions and holes. In ...

. The

forms owing to the difference of

mobilities Mobilities is a contemporary paradigm in the social sciences that explores the movement of people (human migration, individual mobility, travel, transport), ideas (see e.g. meme) and things (transport), as well as the broader social implications of ...

(or

diffusion Diffusion is the net movement of anything (for example, atoms, ions, molecules, energy) generally from a region of higher concentration to a region of lower concentration. Diffusion is driven by a gradient in Gibbs free energy or chemical p ...

constants) for

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 ...

and

electrons 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 ...

which combined with the break of symmetry provided by the surface lead to an effective charge separation in the direction perpendicular to the surface. In an isolated sample, where the macroscopic flow of an electric current is prohibited, the fast carriers (often the electrons) are slowed and the slow carriers (often the holes) are accelerated by an electric field, called the Dember field. One of the main applications of the photo–Dember effect is the generation of terahertz (THz) radiation pulses for

terahertz time-domain spectroscopy In physics, terahertz time-domain spectroscopy (THz-TDS) is a spectroscopic technique in which the properties of matter are probed with short pulses of terahertz radiation. The generation and detection scheme is sensitive to the sample's effect ...

. This effect is present in most semiconductors but it is particularly strong in

narrow-gap semiconductor Narrow-gap semiconductors are semiconducting materials with a magnitude of bandgap that is smaller than 0.7 eV, which corresponds to an infrared absorption cut-off wavelength over 2.5 micron. A more extended definition includes all semiconductors w ...

s (mainly

arsenide In chemistry, an arsenide is a compound of arsenic with a less electronegative element or elements. Many metals form binary compounds containing arsenic, and these are called arsenides. They exist with many Stoichiometry, stoichiometries, and in t ...

s and

antimonide Antimonides (sometimes called stibnides or stibinides) are compounds of antimony with more electropositive elements. The antimonide ion is but the term refers also to any anionic derivative of antimony. Antimonides are often prepared by heating ...

s) such as InAs and

InSb Indium antimonide (InSb) is a crystalline compound made from the elements indium (In) and antimony (Sb). It is a narrow- gap semiconductor material from the III- V group used in infrared detectors, including thermal imaging cameras, FLIR syst ...

owing to their high

electron mobility In solid-state physics, the electron mobility characterizes how quickly an electron can move through a metal or semiconductor when pushed or pulled by an electric field. There is an analogous quantity for Electron hole, holes, called hole mobilit ...

. The photo–Dember terahertz emission should not be confused with the surface

field emission Field electron emission, also known as field-induced electron emission, field emission (FE) and electron field emission, is the emission of electrons from a material placed in an electrostatic field. The most common context is field emission from ...

, which occurs if the surface

energy band In solid-state physics, the electronic band structure (or simply band structure) of a solid describes the range of energy levels that electrons may have within it, as well as the ranges of energy that they may not have (called ''band gaps'' or '' ...

s of a

fall between its valence and

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 ...

bands, which produces a phenomenon known as

Fermi level pinning Enrico Fermi (; 29 September 1901 – 28 November 1954) was an Italian and naturalized American physicist, renowned for being the creator of the world's first artificial nuclear reactor, the Chicago Pile-1, and a member of the Manhattan Project ...

, causing, at its time,

band bending In solid-state physics, band bending refers to the process in which the electronic band structure in a material curves up or down near a junction or interface. It does not involve any physical (spatial) bending. When the electrochemical potential ...

and consequently the formation of a depletion or accumulation layer close to the surface which contributes to the

acceleration In mechanics, acceleration is the Rate (mathematics), rate of change of the velocity of an object with respect to time. Acceleration is one of several components of kinematics, the study of motion. Accelerations are Euclidean vector, vector ...

. These two effects can contribute constructively or destructively for the

formation depending on the direction of the band-bending.

References

{{DEFAULTSORT:Photo-Dember effect Semiconductors Terahertz technology Optoelectronics

See also

References