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42-411: The axion is a hypothetical elementary particle originally postulated to solve the strong CP problem . The axion is also an extremely attractive dark matter candidate. The axion is the puzzle piece allowing these two mysteries to fit naturally into our understanding of the universe. The axion was originally postulated to exist as part of the solution to the "strong CP problem". This problem arose from

84-722: A HEMT device, the D-HEMT, was presented by Mimura and Satoshi Hiyamizu in May 1980, and then they later demonstrated the first E-HEMT in August 1980. Independently, Daniel Delagebeaudeuf and Tranc Linh Nuyen, while working at Thomson-CSF in France, filed a patent for a similar type of field-effect transistor in March 1979. It also cites the Bell Labs patent as an influence. The first demonstration of an "inverted" HEMT

126-461: A junction at equilibrium similar to a p–n junction . Note that the undoped narrow band gap material now has excess majority charge carriers. The fact that the charge carriers are majority carriers yields high switching speeds, and the fact that the low band gap semiconductor is undoped means that there are no donor atoms to cause scattering and thus yields high mobility. In the case of GaAs HEMTs, they make use of high mobility electrons generated using

168-436: A new particle called the axion . If the axion is very light, it interacts so weakly that it would be nearly impossible to detect but would be an ideal dark matter candidate. The ADMX experiment aims to detect this extraordinarily weakly coupled particle. Although dark matter can't be seen directly, its gravitational interactions with familiar matter leave unmistakable evidence for its existence. The universe today would not look

210-517: A small voltage as a control signal. Both of these uses are made possible by the FET’s unique current–voltage characteristics . HEMT transistors are able to operate at higher frequencies than ordinary transistors, up to millimeter wave frequencies, and are used in high-frequency products such as cell phones , satellite television receivers, voltage converters , and radar equipment. They are widely used in satellite receivers, in low power amplifiers and in

252-485: A strained SiGe layer. In the strained layer, the germanium content increases linearly to around 40-50%. This concentration of germanium allows the formation of a quantum well structure with a high conduction band offset and a high density of very mobile charge carriers . The end result is a FET with ultra-high switching speeds and low noise. InGaAs / AlGaAs , AlGaN / InGaN , and other compounds are also used in place of SiGe. InP and GaN are starting to replace SiGe as

294-428: A yoctowatt) into the cavity. An extraordinarily sensitive microwave receiver allows the weak axion signal to be extracted from the noise. The experiment receiver features quantum-limited noise performance delivered by a Superconducting QUantum Interference Device (SQUID) amplifier and lower temperatures from a He refrigerator. ADMX is the first experiment sensitive to realistic dark-matter axion masses and couplings and

336-710: Is a field-effect transistor incorporating a junction between two materials with different band gaps (i.e. a heterojunction ) as the channel instead of a doped region (as is generally the case for a MOSFET ). A commonly used material combination is GaAs with AlGaAs , though there is wide variation, dependent on the application of the device. Devices incorporating more indium generally show better high-frequency performance, while in recent years, gallium nitride HEMTs have attracted attention due to their high-power performance. Like other FETs , HEMTs can be used in integrated circuits as digital on-off switches. FETs can also be used as amplifiers for large amounts of current using

378-416: Is a secondary ADMX experiment demonstrating the use of dielectrically loaded Fabry–Pérot cavity to search for higher mass axions and dark photons near 70 μeV. In 2022, Orpheus reported results of a first search between 65.5 μeV (15.8 GHz) and 69.3 μeV (16.8 GHz). With hardware upgrades, Orpheus is projected to perform searches from 45 to 80 μeV. Axion Too Many Requests If you report this error to

420-432: Is positive, causing the 2D electron gas to be formed even if there is no doping. Such a transistor is normally on, and will turn off only if the gate is negatively biased - thus this kind of HEMT is known as depletion HEMT , or dHEMT . By sufficient doping of the barrier with acceptors (e.g. Mg ), the built-in charge can be compensated to restore the more customary eHEMT operation, however high-density p-doping of nitrides

462-432: Is so small that the entire experiment is cooled to well below 4.2 kelvin with a liquid helium refrigerator to minimize thermal noise. The electric field within the cavity is sampled by a tiny antenna connected to an ultra-low-noise microwave receiver. The ultra-low noise microwave receiver makes the experiment possible. The dominant background is thermal noise arising from the cavity and the receiver electronics. Signals from

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504-532: Is technologically challenging due to dopant diffusion into the channel. In contrast to a modulation-doped HEMT, an induced high electron mobility transistor provides the flexibility to tune different electron densities with a top gate, since the charge carriers are "induced" to the 2DEG plane rather than created by dopants. The absence of a doped layer enhances the electron mobility significantly when compared to their modulation-doped counterparts. This level of cleanliness provides opportunities to perform research into

546-814: Is to place a buffer layer between them. This is done in the mHEMT or metamorphic HEMT, an advancement of the pHEMT. The buffer layer is made of AlInAs , with the indium concentration graded so that it can match the lattice constant of both the GaAs substrate and the GaInAs channel. This brings the advantage that practically any Indium concentration in the channel can be realized, so the devices can be optimized for different applications (low indium concentration provides low noise ; high indium concentration gives high gain ). HEMTs made of semiconductor hetero-interfaces lacking interfacial net polarization charge, such as AlGaAs/GaAs, require positive gate voltage or appropriate donor-doping in

588-417: Is violated is called a pHEMT or pseudomorphic HEMT. This is achieved by using an extremely thin layer of one of the materials – so thin that the crystal lattice simply stretches to fit the other material. This technique allows the construction of transistors with larger bandgap differences than otherwise possible, giving them better performance. Another way to use materials of different lattice constants

630-503: The bipolar junction transistor and the MOSFET , are the higher operating temperatures, higher breakdown strengths , and lower specific on-state resistances, all in the case of GaN-based HEMTs compared to Si-based MOSFETs. Furthermore, InP-based HEMTs exhibit low noise performance and higher switching speeds. The wide band element is doped with donor atoms; thus it has excess electrons in its conduction band. These electrons will diffuse to

672-504: The wurtzite one, which has built-in electrical polarisation. Since this polarization differs between the GaN channel layer and AlGaN barrier layer, a sheet of uncompensated charge in the order of 0.01-0.03 C/m 2 {\displaystyle ^{2}} is formed. Due to the crystal orientation typically used for epitaxial growth ("gallium-faced") and the device geometry favorable for fabrication (gate on top), this charge sheet

714-524: The AlGaAs barrier to attract the electrons towards the gate, which forms the 2D electron gas and enables conduction of electron currents. This behaviour is similar to that of commonly used field-effect transistors in the enhancement mode, and such a device is called enhancement HEMT, or eHEMT . When a HEMT is built from AlGaN / GaN , higher power density and breakdown voltage can be achieved. Nitrides also have different crystal structure with lower symmetry, namely

756-466: The AlGaAs layer are transferred to the undoped GaAs layer where they form a two dimensional high mobility electron gas within 100 ångström (10 nm ) of the interface. The n-type AlGaAs layer of the HEMT is depleted completely through two depletion mechanisms: The Fermi level of the gate metal is matched to the pinning point, which is 1.2 eV below the conduction band. With the reduced AlGaAs layer thickness,

798-511: The Center for Experimental Physics and Astrophysics (CENPA) at the University of Washington . Led by Dr. Leslie Rosenberg, ADMX is undergoing an upgrade that will allow it to be sensitive to a broad range of plausible dark matter axion masses and couplings. The experiment is designed to detect the weak conversion of dark matter axions into microwave photons in the presence of a strong magnetic field. If

840-473: The Wikimedia System Administrators, please include the details below. Request from 172.68.168.237 via cp1104 cp1104, Varnish XID 841445408 Upstream caches: cp1104 int Error: 429, Too Many Requests at Fri, 29 Nov 2024 06:53:03 GMT HFET A high-electron-mobility transistor ( HEMT or HEM FET ), also known as heterostructure FET ( HFET ) or modulation-doped FET ( MODFET ),

882-406: The adjacent narrow band material’s conduction band due to the availability of states with lower energy. The movement of electrons will cause a change in potential and thus an electric field between the materials. The electric field will push electrons back to the wide band element’s conduction band. The diffusion process continues until electron diffusion and electron drift balance each other, creating

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924-462: The apparatus to 100 mK or less, reducing the noise to 150 mK, which makes data taking 400 times faster. This makes it the "Definitive Experiment". The Haloscope at Yale Sensitive to Axion CDM, or HAYSTAC (formerly known as ADMX-High Frequency), hosted at Yale University , is using a Josephson Parametric Amplifier, 9 T magnet, and microwave cavity with radius of 5 cm and height 25 cm to search masses 19–24 μeV. ADMX-Orpheus

966-661: The base material in MODFETs because of their better noise and power ratios. Ideally, the two different materials used for a heterojunction would have the same lattice constant (spacing between the atoms). In practice, the lattice constants are typically slightly different (e.g. AlGaAs on GaAs), resulting in crystal defects. As an analogy, imagine pushing together two plastic combs with a slightly different spacing. At regular intervals, you'll see two teeth clump together. In semiconductors, these discontinuities form deep-level traps and greatly reduce device performance. A HEMT where this rule

1008-403: The boundary of the two regions inside the narrow band gap material. The accumulation of electrons leads to a very high current in these devices. The term " modulation doping " refers to the fact that the dopants are spatially in a different region from the current carrying electrons. This technique was invented by Horst Störmer at Bell Labs . MODFETs can be manufactured by epitaxial growth of

1050-453: The cavity are amplified by a Superconducting QUantum Interference Device (SQUID) amplifier followed by ultralow noise cryogenic HFET amplifiers. The receiver then downconverts microwave cavity frequencies to a lower frequency that can be easily digitized and saved. The receiver chain is sensitive to powers smaller than 10 rontowatts; this is the world's lowest-noise microwave receiver in a production environment. In 2010, ADMX eliminated one of

1092-423: The conduction and valence bands can be modified separately. This allows the type of carriers in and out of the device to be controlled. As HEMTs require electrons to be the main carriers, a graded doping can be applied in one of the materials, thus making the conduction band discontinuity smaller and keeping the valence band discontinuity the same. This diffusion of carriers leads to the accumulation of electrons along

1134-464: The conduction band on the GaAs side where the electrons can move quickly without colliding with any impurities because the GaAs layer is undoped, and from which they cannot escape. The effect of this is the creation of a very thin layer of highly mobile conducting electrons with very high concentration, giving the channel very low resistivity (or to put it another way, "high electron mobility"). Since GaAs has higher electron affinity , free electrons in

1176-407: The dark matter accounting for the bulk of all matter in our universe is axions, ADMX is one of only a few experiments able to detect it. Pierre Sikivie invented the axion haloscope in 1983. After smaller scale experiments at the University of Florida demonstrated the practicality of the axion haloscope, ADMX was constructed at Lawrence Livermore National Laboratory in 1995. In 2010 ADMX moved to

1218-439: The defense industry. The applications of HEMTs include microwave and millimeter wave communications , imaging, radar , radio astronomy , and power switching . They are found in many types of equipment ranging from cellphones, power supply adapters and DBS receivers to radio astronomy and electronic warfare systems such as radar systems. Numerous companies worldwide develop, manufacture, and sell HEMT-based devices in

1260-418: The electrons supplied by donors in the AlGaAs layer are insufficient to pin the layer. As a result, band bending is moving upward and the two-dimensional electrons gas does not appear. When a positive voltage greater than the threshold voltage is applied to the gate, electrons accumulate at the interface and form a two-dimensional electron gas. An important aspect of HEMTs is that the band discontinuities across

1302-687: The form of discrete transistors, as 'monolithic microwave integrated circuits' ( MMICs ), or within power switching integrated circuits. HEMTs are suitable for applications where high gain and low noise at high frequencies are required, as they have shown current gain to frequencies greater than 600 GHz and power gain to frequencies greater than 1THz. Gallium nitride based HEMTs are used as power switching transistors for voltage converter applications due to their low on-state resistances, low switching losses, and high breakdown strength. These gallium nitride enhanced voltage converter applications include AC adapters , which benefit from smaller package sizes due to

Axion Dark Matter Experiment - Misplaced Pages Continue

1344-496: The formation of a two-dimensional electron gas ( 2DEG ) are known as HEMTs. In HEMTS electric current flows between a drain and source element via the 2DEG, which is located at the interface between two layers of differing band gaps , termed the heterojunction . Some examples of previously explored heterojunction layer compositions (heterostructures) for HEMTs include AlGaN/GaN, AlGaAs/GaAs, InGaAs/GaAs, and Si/SiGe. The advantages of HEMTs over other transistor architectures, like

1386-426: The heterojunction of a highly doped wide-bandgap n-type donor-supply layer (AlGaAs in our example) and a non-doped narrow-bandgap channel layer with no dopant impurities (GaAs in this case). The electrons generated in the thin n-type AlGaAs layer drop completely into the GaAs layer to form a depleted AlGaAs layer, because the heterojunction created by different band-gap materials forms a quantum well (a steep canyon) in

1428-477: The hypothesis is correct, an apparatus consisting of an 8  tesla magnet and a cryogenically cooled high-Q tunable microwave cavity should stimulate the conversion of axions into photons. When the cavity's resonant frequency is tuned to the axion mass, the interaction between nearby axions in the Milky Way halo and ADMX's magnetic field is enhanced. This results in the deposit of a tiny amount of power (less than

1470-438: The improved detector allows a more sensitive search. The microwave cavity within the magnet bore is at the heart of ADMX. It is a circular cylinder, 1 meter long and 0.5 meter diameter. ADMX searches for axions by slowly scanning the cavity resonant frequency by adjusting positions of two tuning rods within the cavity. A signal appears when the cavity resonant frequency matches the axion mass. The expected signal from axion decay

1512-462: The noise (to less than 100 mK) and vastly improved sensitivity. ADMX has demonstrated that the SQUID amplifier allows for quantum-limited-power sensitivity. In 2016, ADMX acquired Josephson Parametric Amplifiers which allow quantum noise limited searches at higher frequencies. The addition of a dilution refrigerator was the main focus of the 2016 upgrade program. The dilution refrigerator allows cooling

1554-400: The observation that the strong force holding nuclei together and the weak force making nuclei decay differ in the amount of CP violation in their interactions. Weak interaction was expected to feed into the strong interactions ( QCD ), yielding appreciable QCD CP violation, but no such violation has been observed to very high accuracy. One solution to this Strong CP Problem introduces

1596-498: The power circuitry requiring smaller passive electronic components. The invention of the high-electron-mobility transistor (HEMT) is usually attributed to physicist Takashi Mimura (三村 高志), while working at Fujitsu in Japan. The basis for the HEMT was the GaAs (gallium arsenide) MOSFET (metal–oxide–semiconductor field-effect transistor), which Mimura had been researching as an alternative to

1638-441: The same without dark matter. Approximately five times more abundant than ordinary matter, the nature of dark matter remains one of the biggest mysteries in physics. In addition to solving the strong CP problem , the axion could provide an answer to the question "what is dark matter made of?" The axion is a neutral particle that is extraordinarily weakly interacting and could be produced in the right amount to constitute dark matter. If

1680-566: The standard silicon (Si) MOSFET since 1977. He conceived the HEMT in Spring 1979, when he read about a modulated-doped heterojunction superlattice developed at Bell Labs in the United States, by Ray Dingle, Arthur Gossard and Horst Störmer who filed a patent in April 1978. Mimura filed a patent disclosure for a HEMT in August 1979, and then a patent later that year. The first demonstration of

1722-522: The two axion benchmark models from 1.9 μeV to 3.53 μeV, assuming axions saturate the Milky Way's halo. A 2016 upgrade should allow the ADMX to exclude or discover 1 μeV to 40 μeV dark matter axions. In the first implementation of the experiment in 1996, the amplifier noise temperature was around 2 K. In 2009, the first stage amplifier was replaced by a SQUID amplifier, which greatly lowered

Axion Dark Matter Experiment - Misplaced Pages Continue

1764-496: Was presented by Delagebeaudeuf and Nuyen in August 1980. One of the earliest mentions of a GaN-based HEMT is in the 1993 Applied Physics Letters article, by Khan et al . Later, in 2004, P.D. Ye and B. Yang et al demonstrated a GaN (gallium nitride) metal–oxide–semiconductor HEMT (MOS-HEMT). It used atomic layer deposition (ALD) aluminum oxide (Al 2 O 3 ) film both as a gate dielectric and for surface passivation . Field effect transistors whose operation relies on

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