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 l ...

the Ridley–Watkins–Hilsum theory (RWH) explains the mechanism by which differential

negative resistance In electronics, negative resistance (NR) is a property of some electrical circuits and devices in which an increase in voltage across the device's terminals results in a decrease in electric current through it. This is in contrast to an ordi ...

is developed in a bulk solid state

semiconductor A semiconductor is a material which has an electrical conductivity value falling between that of a conductor, such as copper, and an insulator, such as glass. Its resistivity falls as its temperature rises; metals behave in the opposite way. ...

material when a voltage is applied to the terminals of the sample. It is the theory behind the operation of the

Gunn diode A Gunn diode, also known as a transferred electron device (TED), is a form of diode, a two-terminal semiconductor electronic component, with negative resistance, used in high-frequency electronics. It is based on the "Gunn effect" discovered in ...

as well as several other microwave semiconductor devices, which are used practically in

electronic oscillator An electronic oscillator is an electronic circuit that produces a periodic, oscillating electronic signal, often a sine wave or a square wave or a triangle wave. Oscillators convert direct current (DC) from a power supply to an alternating cur ...

s to produce

microwave Microwave is a form of electromagnetic radiation with wavelengths ranging from about one meter to one millimeter corresponding to frequency, frequencies between 300 MHz and 300 GHz respectively. Different sources define different fre ...

power. It is named for British physicists Brian Ridley, Tom Watkins and

Cyril Hilsum Cyril Hilsum (born 17 May 1925) is a British physicist and academic. Hilsum was elected a member of the National Academy of Engineering in 1983 for the inventiveness and leadership in introducing III-V semiconductors into electronic technology ...

who wrote theoretical papers on the effect in 1961. Negative resistance oscillations in bulk semiconductors had been observed in the laboratory by J. B. Gunn in 1962, and were thus named the "Gunn effect", but physicist

Herbert Kroemer Herbert Kroemer (; born August 25, 1928) is a German-American physicist who, along with Zhores Alferov, received the Nobel Prize in Physics in 2000 for "developing semiconductor heterostructures used in high-speed- and opto-electronics". Kroemer ...

pointed out in 1964 that Gunn's observations could be explained by the RWH theory. In essence, RWH mechanism is the transfer of conduction electrons in a semiconductor from a high

mobility Mobility may refer to: Social sciences and humanities * Economic mobility, ability of individuals or families to improve their economic status * Geographic mobility, the measure of how populations and goods move over time * Mobilities, a conte ...

valley to lower-mobility, higher-energy satellite valleys. This phenomenon can only be observed in materials that have such

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 '' ...

structures. Normally, in a conductor, increasing electric field causes higher charge

carrier Carrier may refer to: Entertainment * ''Carrier'' (album), a 2013 album by The Dodos * ''Carrier'' (board game), a South Pacific World War II board game * ''Carrier'' (TV series), a ten-part documentary miniseries that aired on PBS in April 20 ...

(usually electron) speeds and results in higher current consistent with

Ohm's law Ohm's law states that the current through a conductor between two points is directly proportional to the voltage across the two points. Introducing the constant of proportionality, the resistance, one arrives at the usual mathematical equatio ...

. In a multi-valley semiconductor, though, higher energy may push the carriers into a higher energy state where they actually have higher effective mass and thus slow down. In effect, carrier velocities and current drop as the voltage is increased. While this transfer occurs, the material exhibits a decrease in current – that is, a negative differential resistance. At higher voltages, the normal increase of current with voltage relation resumes once the bulk of the carriers are kicked into the higher energy-mass valley. Therefore the negative resistance only occurs over a limited range of voltages. Of the type of semiconducting materials satisfying these conditions, gallium arsenide (GaAs) is the most widely understood and used. However RWH mechanisms can also be observed in

indium phosphide Indium phosphide (InP) is a binary semiconductor composed of indium and phosphorus. It has a face-centered cubic (" zincblende") crystal structure, identical to that of GaAs and most of the III-V semiconductors. Manufacturing Indium phosphide c ...

(InP),

cadmium telluride Cadmium telluride (CdTe) is a stable crystalline compound formed from cadmium and tellurium. It is mainly used as the semiconducting material in cadmium telluride photovoltaics and an infrared optical window. It is usually sandwiched with cadm ...

(CdTe),

zinc selenide Zinc selenide (ZnSe) is a light-yellow, solid compound comprising zinc (Zn) and selenium (Se). It is an intrinsic semiconductor with a band gap of about 2.70 eV at . ZnSe rarely occurs in nature, and is found in the mineral that was named af ...

(ZnSe) and

indium arsenide Indium arsenide, InAs, or indium monoarsenide, is a narrow-bandgap semiconductor composed of indium and arsenic. It has the appearance of grey cubic crystals with a melting point of 942 °C. Indium arsenide is similar in properties to galliu ...

(InAs) under hydrostatic or uniaxial pressure.

References

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* * * * * Electronic engineering {{CMP-stub de:Gunn-Effekt

See also

References

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