Journal articles: 'Two Dimensional Electron Systems (2DES)'

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Satou, Akira, and Koichi Narahara. "Numerical Characterization of Dyakonov-Shur Instability in Gated Two-Dimensional Electron Systems." International Journal of High Speed Electronics and Systems 25, no. 03n04 (September 2016): 1640024. http://dx.doi.org/10.1142/s0129156416400243.

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We numerically analyze the system based on the essentially non-oscillatory shock capturing scheme in order to characterize the Dyakonov-Shur (DS) instability in a gated two-dimensional electron gas system (2DES). The predictions of the linearized model are examined for a 2DES sandwiched by the top and back metallic gates. By solving Poisson equation self-consistently, the dispersive properties of plasma wave are properly estimated. Special attention is paid to the impact of dispersion to nonlinear dynamics of plasma-wave oscillation. A single-gated 2DES is also investigated for demonstrating the DS instability in practical devices.

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Freeman, M. L., Tzu-Ming Lu, and L. W. Engel. "Resistively loaded coplanar waveguide for microwave measurements of induced carriers." Review of Scientific Instruments 93, no. 4 (April 1, 2022): 043901. http://dx.doi.org/10.1063/5.0085112.

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We describe the use of a coplanar waveguide (CPW) whose slots are filled with a resistive film, a resistively loaded CPW (RLCPW), to measure two-dimensional electron systems (2DESs). The RLCPW applied to the sample hosting the 2DES provides a uniform metallic surface serving as a gate to control the areal charge density of the 2DES. As a demonstration of this technique, we present measurements on a Si metal–oxide–semiconductor field-effect transistor and a model that successfully converts microwave transmission coefficients into conductivity of a nearby 2DES capacitively coupled to the RLCPW. We also describe the process of fabricating the highly resistive metal film required for fabrication of the RLCPW.

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D’Antuono, M., A. Kalaboukhov, R. Caruso, S. Wissberg, S. Weitz Sobelman, B. Kalisky, G. Ausanio, M. Salluzzo, and D. Stornaiuolo. "Nanopatterning of oxide 2-dimensional electron systems using low-temperature ion milling." Nanotechnology 33, no. 8 (November 30, 2021): 085301. http://dx.doi.org/10.1088/1361-6528/ac385e.

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Abstract We present a ‘top-down’ patterning technique based on ion milling performed at low-temperature, for the realization of oxide two-dimensional electron system devices with dimensions down to 160 nm. Using electrical transport and scanning Superconducting QUantum Interference Device measurements we demonstrate that the low-temperature ion milling process does not damage the 2DES properties nor creates oxygen vacancies-related conducting paths in the STO substrate. As opposed to other procedures used to realize oxide 2DES devices, the one we propose gives lateral access to the 2DES along the in-plane directions, finally opening the way to coupling with other materials, including superconductors.

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Verseils, Marine, Alexandre Voute, Benjamin Langerome, Maxime Deutsch, Jean-Blaise Brubach, Alexei Kalaboukhov, Alessandro Nucara, Paolo Calvani, and Pascale Roy. "Grazing-angle reflectivity setup for the low-temperature infrared spectroscopy of two-dimensional systems." Journal of Synchrotron Radiation 26, no. 6 (September 11, 2019): 1945–50. http://dx.doi.org/10.1107/s1600577519010920.

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A new optical setup is described that allows the reflectivity at grazing incidence to be measured, including ultrathin films and two-dimensional electron systems (2DES) down to liquid-helium temperatures, by exploiting the Berreman effect and the high brilliance of infrared synchrotron radiation. This apparatus is well adapted to detect the absorption of a 2DES of nanometric thickness, namely that which forms spontaneously at the interface between a thin film of LaAlO3 and its SrTiO3 substrate, and to determine its Drude parameters.

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PHONG, TRAN CONG, VO THANH LAM, and LUONG VAN TUNG. "CALCULATION OF THE INTENSITY-DEPENDENT ABSORPTION SPECTRUM IN TWO-DIMENSIONAL ELECTRON SYSTEMS." Modern Physics Letters B 25, no. 11 (May 10, 2011): 863–72. http://dx.doi.org/10.1142/s0217984911026061.

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General analytic expression for the intensity-dependent absorption coefficient (IDAC) of an intense electromagnetic wave (IEMW) in two-dimensional electron systems (2DES) is obtained by using the quantum kinetic equation (QKE) for electrons in the case of electron–optical phonon scattering in a doped semiconductor superlattice (DSSL). The dependence of IDAC on the amplitude E0 and the photon energy ℏΩ of an IEMW, the energy ℏωp and the temperature for a specific n-i-p-i superlattice of GaAs : Si / GaAs : Be is achieved due to a numerical method. The computational results show that not only the dependence of IDAC on ℏΩ but also the dependence of IDAC on ℏωp can be applied to optically detect the electric subbands in a DSSL.

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CHEBOTAREV, ANDREY, and GALINA CHEBOTAREVA. "CYCLOTRON RESONANCE VANISHING EFFECT AND THz DETECTION." International Journal of High Speed Electronics and Systems 18, no. 04 (December 2008): 959–69. http://dx.doi.org/10.1142/s0129156408005916.

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Experimental measurements of photoresistivity under terahertz (THz) radiation in low magnetic fields at conditions of cyclotron resonance (CR) in two-dimensional electron system (2DES) of GaAs / AlGaAs nanostructures are presented and discussed. We report the experimental discovery of "CR-vanishing effect" (CRV) in GaAs / AlGaAs heterostructures with high mobility as a well-defined gap on CR-line that is independent on incident THz power. Our analysis shows that the CRV may appear in systems with well correlated state of 2D electrons such as plasma waves and others. Fundamental nature of these correlated states of electrons in 2DES is discussed. Future THz detectors utilizing the new correlated states in 2DES may expand horizons for supersensitive detection in sub-THz and THz frequencies ranges.

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Cangas, R., and M. A. Hidalgo. "Influence of the Spin–Orbit Interaction on the Magnetotransport Properties of a Two-Dimensional Electron System." SPIN 05, no. 03 (September 2015): 1530003. http://dx.doi.org/10.1142/s2010324715300030.

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In this paper, we review the contribution of the Rashba spin–orbit coupling to the magnetoconduction of a two-dimensional electron system (2DES) confined in an inversion layer under quantum Hall regime (low temperature and low defects and impurities). The study is based on a semi-classical model for the magnetoconductivities of the 2DES. This model reproduces the measurements of the Shubnikov-de Haas (SdH) oscillations obtained in systems confined in III–V heterostructures, and also the quantum Hall magnetoconductivity (magnetoresistivity). We also discuss the Rashba and Zeeman competition and its effect on the magnetoconductivity.

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MORGENSTERN, MARKUS. "PROBING THE LOCAL DENSITY OF STATES OF DILUTE ELECTRON SYSTEMS IN DIFFERENT DIMENSIONS." Surface Review and Letters 10, no. 06 (December 2003): 933–62. http://dx.doi.org/10.1142/s0218625x0300575x.

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Scanning tunneling spectroscopy at T = 6 K is used to investigate the local density of states (LDOS) of electron systems belonging to the bulk conduction band of InAs. In particular, the three-dimensional electron system (3DES) of the n-doped material, an adsorbate-induced two-dimensional electron system (2DES) and the tip-induced quantum dot (0DES) are investigated at B = 0 T and B = 6 T. It is found that the 3DES at B = 0 T can be described by Bloch states weakly interacting with the potential disorder provided by ionized dopants. The 2DES at B = 0 T exhibits much stronger LDOS corrugations, stressing the tendency for weak localization in the potential disorder. In a magnetic field, 3DES and 2DES show drift states, which are expected in 2D, but are surprising in 3D, where they point to a new electron phase consisting of droplets of quasi-2D systems. The 0DES at B = 0 T reveals quantized states in accordance with Hartree calculations. At B = 6 T it exhibits Landau states with exchange enhanced spin splitting. These states are used to investigate the influence of potential disorder on the exchange enhancement, which visualizes the nonlocality of the exchange interaction.

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BAENNINGER, MATTHIAS, ARINDAM GHOSH, MICHAEL PEPPER, HARVEY E. BEERE, IAN FARRER, and DAVID A. RITCHIE. "MAGNETIC FIELD INDUCED INSTABILITIES IN LOCALIZED TWO-DIMENSIONAL ELECTRON SYSTEMS." International Journal of Modern Physics B 23, no. 12n13 (May 20, 2009): 2708–12. http://dx.doi.org/10.1142/s0217979209062232.

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The results of extensive transport studies in localized regime of mesoscopic two-dimensional electron systems (2DES) with varying disorder are presented. A quick overview of previously achieved result is given. The main focus is on the observation of density dependent instabilities manifested by strong resistance oscillations induced by high perpendicular magnetic fields B⊥. While the amplitude of the oscillations is strongly enhanced with increasing B⊥, their position in electron density remains unaffected. The temperature dependence of resistivity shows a transition from an activated behaviour at high temperature to a saturated behaviour at low T. In the positions of resistance minima, the T dependence can even become metal-like (dρ/dT > 0). The activation energies obtained from the high T behaviour exhibit a formation of plateaux in connection with the resistance oscillations when analyzed as a function of electron density. We suggest the interplay between a strongly interacting electron phase and the background disorder as a possible explanation for our observation.

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DOHI, M., R. YONAMINE, K. OTO, and K. MURO. "POTENTIAL IMAGING IN QUANTUM HALL DEVICES BY OPTICAL FIBER BASED POCKELS MEASUREMENT." International Journal of Modern Physics B 21, no. 08n09 (April 10, 2007): 1414–18. http://dx.doi.org/10.1142/s0217979207042926.

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We have developed an optical-fiber-based Hall potential imaging system using the Pockels effect in GaAs/AlGaAs two dimensional electron systems (2DES) in the quantum Hall regime to investigate current distributions. The mapping of the Hall potential shows the current concentration at the bulk region of 2DES samples, where the critical current depends on the channel width sub-linearly. We report in detail the experimental techniques of the imaging system operating in high magnetic fields.

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Hatke, A. T., H. Deng, Yang Liu, L. W. Engel, L. N. Pfeiffer, K. W. West, K. W. Baldwin, and M. Shayegan. "Wigner solid pinning modes tuned by fractional quantum Hall states of a nearby layer." Science Advances 5, no. 3 (March 2019): eaao2848. http://dx.doi.org/10.1126/sciadv.aao2848.

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We studied a bilayer system hosting two-dimensional electron systems (2DESs) in close proximity but isolated from one another by a thin barrier. One 2DES has low electron density and forms a Wigner solid (WS) at high magnetic fields. The other has much higher density and, in the same field, exhibits fractional quantum Hall states (FQHSs). The WS spectrum has resonances which are understood as pinning modes, oscillations of the WS within the residual disorder. We found the pinning mode frequencies of the WS are strongly affected by the FQHSs in the nearby layer. Analysis of the spectra indicates that the majority layer screens like a dielectric medium even when its Landau filling is ~1/2, at which the layer is essentially a composite fermion (CF) metal. Although the majority layer is only ~ one WS lattice constant away, a WS site only induces an image charge of ~0.1e in the CF metal.

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DAHAN, PINCHAS, and ISRAEL VAGNER. "HIGH FIELD RESONANT TUNING OF THE NUCLEAR SPIN-QUBIT RELAXATION RATE IN 2DES WITH MAGNETIC IMPURITIES: STRONG SCATTERING LIMIT." International Journal of Modern Physics B 18, no. 27n29 (November 30, 2004): 3865–70. http://dx.doi.org/10.1142/s021797920402761x.

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The strong scattering limit of the magnetic field dependence of the local phonon-assisted nuclear spin relaxation rate, (NSRR), in two dimensional electron systems, (2DES) with magnetic impurities is calculated. It is shown that the NSRR can be tuned resonantly, by external magnetic field, due to the possibility of matching the electron Zeeman splitting with the energy spacing between the localized vibrational modes created by the lattice distortion around the impurity. This new resonance phenomenon could be used to manipulate, with high precision, the relaxation and decoherence times of nuclear spin based quantum information processing devices.

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13

Meng, You, Fangzhou Li, Changyong Lan, Xiuming Bu, Xiaolin Kang, Renjie Wei, SenPo Yip, et al. "Artificial visual systems enabled by quasi–two-dimensional electron gases in oxide superlattice nanowires." Science Advances 6, no. 46 (November 2020): eabc6389. http://dx.doi.org/10.1126/sciadv.abc6389.

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Rapid development of artificial intelligence techniques ignites the emerging demand on accurate perception and understanding of optical signals from external environments via brain-like visual systems. Here, enabled by quasi–two-dimensional electron gases (quasi-2DEGs) in InGaO3(ZnO)3 superlattice nanowires (NWs), an artificial visual system was built to mimic the human ones. This system is based on an unreported device concept combining coexistence of oxygen adsorption-desorption kinetics on NW surface and strong carrier quantum-confinement effects in superlattice core, to resemble the biological Ca2+ ion flux and neurotransmitter release dynamics. Given outstanding mobility and sensitivity of superlattice NWs, an ultralow energy consumption down to subfemtojoule per synaptic event is realized in quasi-2DEG synapses, which rivals that of biological synapses and now available synapse-inspired electronics. A flexible quasi-2DEG artificial visual system is demonstrated to simultaneously perform high-performance light detection, brain-like information processing, nonvolatile charge retention, in situ multibit-level memory, orientation selectivity, and image memorizing.

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WEXLER, CARLOS, and ORION CIFTJA. "NOVEL LIQUID CRYSTALLINE PHASES IN QUANTUM HALL SYSTEMS." International Journal of Modern Physics B 20, no. 07 (March 20, 2006): 747–78. http://dx.doi.org/10.1142/s0217979206033632.

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Since 1999, experiments have shown a plethora of surprising results in the low-temperature magnetotransport in intermediate regions between quantum Hall (QH) plateaus: the extreme anisotropies observed for half-filling, or the re-entrant integer QH effects at quarter filling of high Landau levels (LL); or even an apparent melting of a Wigner Crystal (WC) at filling factor ν = 1/7 of the lowest LL. A large body of seemingly distinct experimental evidence has been successfully interpreted in terms of liquid crystalline phases in the two-dimensional electron system (2DES). In this paper, we present a review of the physics of liquid crystalline states for strongly correlated two-dimensional electronic systems in the QH regime. We describe a semi-quantitative theory for the formation of QH smectics (stripes), their zero-temperature melting onto nematic phases and ultimate anisotropic-isotropic transition via the Kosterlitz–Thouless (KT) mechanism. We also describe theories for QH-like states with various liquid crystalline orders and their excitation spectrum. We argue that resulting picture of liquid crystalline states in partially filled LL-s is a valuable starting point to understand the present experimental findings, and to suggest new experiments that will lead to further elucidation of this intriguing system.

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Du, Shuo, Yang Guo, Xin Huang, Chi Sun, Zhaoqian Zhang, Leyong Hu, Ruixuan Zheng, et al. "Strain lithography for two-dimensional materials by electron irradiation." Applied Physics Letters 120, no. 9 (February 28, 2022): 093104. http://dx.doi.org/10.1063/5.0082556.

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Strain engineering, aiming to tune physical properties of semiconductors, provides a promising paradigm for modern micro/nanoelectronics. Two-dimensional materials (2DMs) are the ideal candidates for the next generation of strain engineered devices because of their intrinsic exceptional mechanical flexibility and strength. However, conventional strain modulation methods in 2DMs cannot satisfy the demand of future device applications, because strained structures by these methods lack consistency, reproducibility, and design flexibility. Here, based on the photoresist degeneration induced by electron irradiation, we present a non-contact approach to accurately and directly write the strains with designed patterns from the nanometer to micrometer scale in 2DMs. Profit from controllable manipulation of the electron beam, the developed strategy offers a capability for constructing tensile, compress, or complex strains in MoSe2 monolayers; hence, unique electronic structures for unique physical properties can be designed. Aside from 2DMs, this approach is also appropriate for other types of materials such as Au, α-Si, and Al2O3. Its flexibility and IC-compatibility allow our strain lithography methodology promising in accelerating the potential applications of 2DMs in extensive fields ranging from nanoelectromechanical systems, high-performance sensing, and nontraditional photovoltaics to quantum information science.

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XU, W. "FAR-INFRARED EMISSION BY HEATED ELECTRONS IN A TWO-DIMENSIONAL SEMICONDUCTOR SYSTEM." Modern Physics Letters B 10, no. 06 (March 10, 1996): 181–88. http://dx.doi.org/10.1142/s0217984996000225.

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In this letter, we present a detailed theoretical study that explores the possibility to use AlGaAs/GaAs-based two-dimensional semiconductor systems (2DSSs) as the far-infrared (FIR) generators at zero-magnetic field and by electrically heated electrons. A simple model from which the intensity of FIR radiation can be calculated as a function of photon frequency is developed by calculating the electron-energy-loss induced by hot-electron interaction with electromagnetic field, mediated by electron-phonon scattering. The main results obtained from the present study are: (1) in a 2DSS, FIR radiation is mainly generated among the different electronic subbands; (2) the polarization of FIR generated from a 2DSS is along the growth direction; (3) the intensity of FIR radiation increases rapidly with increasing energy excitation, i.e., with electron temperature; (4) the frequency of electromagnetic wave generated is around ω~|εm– εn|/ħ with εn the electronic subband energy; and (5) for an AlGaAs-GaAs-AlGaAs single quantum well structure, the frequency of the FIR emission can be tuned by varying the width of the well layer. We have also studied the influence of electron density, lattice temperature, etc. on the FIR emission by heated electrons in 2DSSs.

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Javaid Iqbal, Muhammad, Dirk Reuter, Andreas Dirk Wieck, and Caspar van der Wal. "Characterization of low-resistance ohmic contacts to a two-dimensional electron gas in a GaAs/AlGaAs heterostructure." European Physical Journal Applied Physics 89, no. 2 (February 2020): 20101. http://dx.doi.org/10.1051/epjap/2020190202.

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The study of electron transport in low-dimensional systems is of importance, not only from a fundamental point of view, but also for future electronic and spintronic devices. In this context heterostructures containing a two-dimensional electron gas (2DEG) are a key technology. In particular GaAs/AlGaAs heterostructures, with a 2DEG at typically 100 nm below the surface, are widely studied. In order to explore electron transport in such systems, low-resistance ohmic contacts are required that connect the 2DEG to macroscopic measurement leads at the surface. Here we report on designing and measuring a dedicated device for unraveling the various resistance contributions in such contacts, which include pristine 2DEG series resistance, the 2DEG resistance under a contact, the contact resistance itself, and the influence of pressing a bonding wire onto a contact. We also report here a recipe for contacts with very low resistance values that remain below 10 Ω for annealing times between 20 and 350 s, hence providing the flexibility to use this method for materials with different 2DEG depths. The type of heating, temperature ramp rate and gas forming used for annealing is found to strongly influence the annealing process and hence the quality of the resulting contacts.

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Jin, Eric N., Lior Kornblum, Charles H. Ahn, and Frederick J. Walker. "Integrating 2D electron gas oxide heterostructures on silicon using rare-earth titanates." MRS Advances 1, no. 4 (2016): 287–92. http://dx.doi.org/10.1557/adv.2016.95.

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ABSTRACTIntegrating oxide heterostructures on silicon has the potential to leverage the multifunctionalities of oxide systems into semiconductor device technology. We present the growth and characterization of two-dimensional electron gas (2DEG) oxide systems LaTiO3/SrTiO3 (LTO/STO) and GdTiO3/SrTiO3 (GTO/STO) on Si(001). We show interface-based conductivity in the oxide films and measure high electron densities ranging from ∼9 × 1013 cm-2 interface-1 in GTO/STO/Si to ∼9 × 1014 cm-2 interface-1 in LTO/STO/Si. We attribute the higher measured carrier density in the LTO/STO films to a higher concentration of interface-bound oxygen vacancies arising from a lower oxygen partial pressure during growth. These vacancies donate conduction electrons and result in an increased measured carrier density. The integration of such 2DEG oxide systems with silicon provides a bridge between the diverse electronic properties of oxide systems and the established semiconductor platform and points toward new devices and functionalities.

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An, Yuan, Kailin Ren, Luqiao Yin, and Jianhua Zhang. "Modeling on Monolithic Integration Structure of AlGaN/InGaN/GaN High Electron Mobility Transistors and LEDs: 2DEG Density and Radiative Recombination." Electronics 12, no. 5 (February 22, 2023): 1087. http://dx.doi.org/10.3390/electronics12051087.

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The monolithic integration structure of the AlGaN/InGaN/GaN−based high electron mobility transistor (HEMT) and light−emitting diode (LED) is attractive in LED lighting and visible light communication (VLC) systems owing to the reduction in parasitic elements by removing metal interconnections. Due to the band−offset and polarization effect, inserting a certain thickness in the InGaN layer into the traditional AlGaN/GaN single heterostructure increases the density of 2DEG to nearly twice the original. At the same time, inserting the InGaN quantum well layer can also improve the luminous efficiency of LED. In this paper, the physical models of two−dimensional electron gas (2DEG) densities and the threshold voltage of AlGaN/InGaN/GaN HEMTs are established and verified with experimental results from the literature. According to the calculation results, the two−dimensional electron gas (2DEG) density in the AlGaN/InGaN/GaN HEMT is 1.47 × 1013 cm−2, and the two−dimensional hole gas (2DHG) density is 0.55 × 1013 cm−2, when Al % = 0.2, In % = 0.1, dAlGaN = 20 nm. In addition, a physical model for the radiative recombination rate in the monolithic integration structure of HEMT−LED is proposed. This work provides a design guideline for AlGaN/InGaN/GaN HEMT and its application in visible light communication systems.

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NITTA, JUNSAKU. "SPIN RELATED TRANSPORT IN RASHBA 2DEG SYSTEMS." International Journal of Modern Physics B 22, no. 01n02 (January 20, 2008): 107. http://dx.doi.org/10.1142/s021797920804613x.

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Transport in mesoscopic conductors is determined not only by orbital motion of carriers but also by quantum interference effect. However, it is well known that the quantum interference such as weak localization is much modified in the presence of spin-orbit interaction (SOI), leading to weak anti-localization. We discuss the origin of the Rashba SOI and spin related mesoscopic transport in InGaAs based two dimensional electron gases (2DEG) affected by the Rashba SOI. It is experimentally shown that the strength of the Rashba SOI in InGaAs 2DEG systems can be controlled by the gate voltage.1 The spin dynamics in solid systems is commonly determined by the competition between Zeeman effect and SOI. The spin relaxation time and dephasing time are studied from weak anti-localization analysis as a function of the relative strength of the Zeeman energy (EZ) and the Rashba SOI energy (E SOI ). The (EZ) was introduced by applying magnetic field parallel to the 2DEG plane. This in-pane magnetic field does not affect the orbital motion of electrons. The spin relaxation time increases with the Zeeman energy. The dephasing time associated with the spin-induced time reversal symmetry (TRS) breaking saturates when EZ becomes comparable to E SOI . Moreover, we show that the spin-induced TRS breaking mechanism is a universal function of the ratio EZ/E SOI within the experimental accuracy.2 Note from Publisher: This article contains the abstract only.

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FARID, BEHNAM. "ON THE RESPONSE OF COMPOSITE FERMIONS TO WEAK ELECTROSTATIC POTENTIALS." International Journal of Modern Physics B 18, no. 22 (September 20, 2004): 3047–55. http://dx.doi.org/10.1142/s0217979204026378.

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We establish that the response to static perturbations of two-dimensional electron systems (2DESs), exposed to magnetic field B, in states with the Landau-level filling fractions ν e close to one such as 1/2, is singularly different from that of 2DESs at small ‖B‖. Thus in addition to demonstrating the severe inadequacy of the treatment of composite fermions as non-interacting particles, we show, in contradiction to a recent theoretical finding, that the physical origin of the observed behavior of the dc longitudinal magneto-resistivity for ν e ≈1/2 in periodically modulated 2DESs remains to be determined.

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Chauhan, Prashant, Candice Thomas, Tyler Lindemann, Geoffrey C. Gardner, J. Gukelberger, M. J. Manfra, and N. P. Armitage. "Measurements of cyclotron resonance of the interfacial states in strong spin–orbit coupled 2D electron gases proximitized with aluminum." Applied Physics Letters 120, no. 14 (April 4, 2022): 142105. http://dx.doi.org/10.1063/5.0087401.

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Two dimensional electron gases (2DEGs) in InAs quantum wells proximitized by aluminum are promising platforms for topological qubits based on Majorana zero modes. However, there are still substantial uncertainties associated with the nature of electronic states at the interface of these systems. It is challenging to probe the properties of these hybridized states as they are buried under a relatively thick aluminum layer. In this work, we have investigated a range of InAs/In1−xGaxAs heterostructures with Al overlayers using high precision time-domain THz spectroscopy (TDTS). Despite the thick metallic overlayer, we observe a prominent cyclotron resonance in a magnetic field that can be associated with the response of the interfacial states. Measurements of the THz range complex Faraday rotation allow the extraction of the sign and magnitude of the effective mass, density of charge carriers, and scattering times of the 2DEG despite the close proximity of the aluminum layer. We discuss the extracted band parameters and connect their values to the known physics of these materials.

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Rodríguez, Eduardo Martín, and Estrella González R. "GaAs/AlGaAs nanoheterostructures: Simulation and application on high mobility transistors." Ingeniería e Investigación 31, no. 1 (January 1, 2011): 144–53. http://dx.doi.org/10.15446/ing.investig.v31n1.20535.

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This work analyses the features of GaAs/AlGaAs heterostructure, highlighting semiconductor junction properties. Charge confinement was produced when two materials having different band-gap were fixed; such high electron concentration is called two-dimensional electron gas (2DEG). Device simulation for smart integrated systems (DESSIS) is simulation software which uses physical models and robust numerical methods for simulating semiconductor devices and 3-5 element heterostructures. Results for different heterostructure doping profiles and voltages are presented in this work. High electron mobility transistors (HEMTs) are one of the most important applications for heterostructures; they work on 30 to 300 GHz frequency ranges. These transistors are simulated in this work; a 1 A/mm2 high current density was obtained in the channel, such value being comparable to other values reported for similar transistors.

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Thalhammer, Stefan, Andreas Hörner, Matthias Küß, Stephan Eberle, Florian Pantle, Achim Wixforth, and Wolfgang Nagel. "GaN Heterostructures as Innovative X-ray Imaging Sensors—Change of Paradigm." Micromachines 13, no. 2 (January 19, 2022): 147. http://dx.doi.org/10.3390/mi13020147.

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Direct conversion of X-ray irradiation using a semiconductor material is an emerging technology in medical and material sciences. Existing technologies face problems, such as sensitivity or resilience. Here, we describe a novel class of X-ray sensors based on GaN thin film and GaN/AlGaN high-electron-mobility transistors (HEMTs), a promising enabling technology in the modern world of GaN devices for high power, high temperature, high frequency, optoelectronic, and military/space applications. The GaN/AlGaN HEMT-based X-ray sensors offer superior performance, as evidenced by higher sensitivity due to intensification of electrons in the two-dimensional electron gas (2DEG), by ionizing radiation. This increase in detector sensitivity, by a factor of 104 compared to GaN thin film, now offers the opportunity to reduce health risks associated with the steady increase in CT scans in today’s medicine, and the associated increase in exposure to harmful ionizing radiation, by introducing GaN/AlGaN sensors into X-ray imaging devices, for the benefit of the patient.

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Tan, Yuting, Vladimir Dobrosavljević, and Louk Rademaker. "How to Recognize the Universal Aspects of Mott Criticality?" Crystals 12, no. 7 (June 30, 2022): 932. http://dx.doi.org/10.3390/cryst12070932.

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In this paper we critically discuss several examples of two-dimensional electronic systems displaying interaction-driven metal-insulator transitions of the Mott (or Wigner–Mott) type, including dilute two-dimension electron gases (2DEG) in semiconductors, Mott organic materials, as well as the recently discovered transition-metal dichalcogenide (TMD) moiré bilayers. Remarkably similar behavior is found in all these systems, which is starting to paint a robust picture of Mott criticality. Most notable, on the metallic side a resistivity maximum is observed whose temperature scale vanishes at the transition. We compare the available experimental data on these systems to three existing theoretical scenarios: spinon theory, Dynamical Mean Field Theory (DMFT) and percolation theory. We show that the DMFT and percolation pictures for Mott criticality can be distinguished by studying the origins of the resistivity maxima using an analysis of the dielectric response.

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ZIMBOVSKAYA, NATALIYA A., and JOSEPH L. BIRMAN. "DEFORMED FERMI SURFACE THEORY OF MAGNETO–ACOUSTIC RESPONSE IN MODULATED QUANTUM HALL SYSTEMS NEAR ν=1/2." International Journal of Modern Physics B 13, no. 08 (March 30, 1999): 859–68. http://dx.doi.org/10.1142/s0217979299000722.

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We develop a magneto-transport theory for the nonlocal response of a two-dimensional electron gas (2DEG) in the Fractional Quantum Hall Regime near ν=1/2 in the presence of a periodic density modulation. We introduce a new generic model of a deformed Composite Fermion–Fermi Surface (CF–FS). Our model permits us to explain recent surface acoustic wave observations of anisotropic anomalies1 in sound velocity and attenuation, such as appearance of peaks and anisotropy, which originate from contributions to the conductivity tensor due to regions of the CF–FS which are flattened by the applied modulation. The calculated magnetic field and wave vector dependence of the CF conductivity, velocity shift and attenuation agree with experiments.

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Sheu, Gene, Yu-Lin Song, Ramyasri Mogarala, Dupati Susmitha, and Kutagulla Issac. "Breakdown Behavior of Metal Contact Positions in GaN HEMT with Nitrogen-Implanted Gate Using TCAD Simulation." Micromachines 13, no. 2 (January 22, 2022): 169. http://dx.doi.org/10.3390/mi13020169.

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In this study, the breakdown behavior of a calibrated depletion mode AlGaN/GaN transistor with a nitrogen-implanted gate region was simulated and analyzed using Sentaurus TCAD simulation, with particular emphasis on the metal contact design rule for a GaN-based high-electron-mobility transistor (HEMT) device with a variety of 2DEG concentrations grown on a silicon substrate. The breakdown behaviors for different source/drain contact schemes were investigated using Sentaurus simulation. The metal contact positions within the source and drain exhibited different piezoelectric effects and induced additional polarization charges for the 2DEG (two-dimensional electron gas). Due to the variation of source/drain contact schemes, electron density has changed the way to increase the electric field distribution, which in turn increased the breakdown voltage. The electric field distribution and 2DEG profiles were simulated to demonstrate that the piezoelectric effects at different metal contact positions considerably influence the breakdown voltage at different distances between drain metal contacts. When the contact position was far away from the AlGaN/GaN, the breakdown voltage of the nitrogen-implanted gated device decreased by 41% because of the relatively low electron density and weak induced piezoelectric effect. This reduction is significant for a 20 μm source-drain length. The minimum critical field used for the breakdown simulation was 4 MV/cm. The simulated AlGaN/GaN device exhibits different breakdown behaviors at different metal contact positions in the drain.

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Zavjalov, Alexey, Sergey Tikhonov, and Denis Kosyanov. "TiO2–SrTiO3 Biphase Nanoceramics as Advanced Thermoelectric Materials." Materials 12, no. 18 (September 7, 2019): 2895. http://dx.doi.org/10.3390/ma12182895.

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The review embraces a number of research papers concerning the fabrication of oxide thermoelectric systems, with TiO2−SrTiO3 biphase ceramics being emphasized. The ceramics is particularly known for a two-dimensional electron gas (2DEG) forming spontaneously on the TiO2/SrTiO3 heterointerface (modulation doping), unlike ordinary 2DEG occurrence on specially fabricated thin film. Such effect is provided by the SrTiO3 conduction band edge being 0.40 and 0.20 eV higher than that for anatase and rutile TiO2, respectively. That is why, in the case of a checkered arrangement of TiO2 and SrTiO3 grains, the united 2D net is probably formed along the grain boundaries with 2DEG occurring there. To reach such conditions, there should be applied novelties in the field of ceramics materials science, because it is important to obtain highly dense material preserving small (nanoscale) grain size and thin interface boundary. The review also discusses some aspects of reactive spark plasma sintering as a promising method of preparing perovskite-oxide TiO2−SrTiO3 thermoelectric materials for high-temperature applications.

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Niu, Di, Quan Wang, Wei Li, Changxi Chen, Jiankai Xu, Lijuan Jiang, Chun Feng, et al. "The Influence of the Different Repair Methods on the Electrical Properties of the Normally off p-GaN HEMT." Micromachines 12, no. 2 (January 26, 2021): 131. http://dx.doi.org/10.3390/mi12020131.

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The influence of the repair process on the electrical properties of the normally off p-GaN high-electron-mobility transistor (HEMT) is studied in detail in this paper. We find that the etching process will cause the two-dimensional electron gas (2DEG) and the mobility of the p-GaN HEMT to decrease. However, the repair process will gradually recover the electrical properties. We study different repair methods and different repair conditions, propose the best repair conditions, and further fabricate the p-GaN HEMTs devices. The threshold voltage of the fabricated device is 1.6 V, the maximum gate voltage is 7 V, and the on-resistance is 23 Ω·mm. The device has a good performance, which proves that the repair conditions can be successfully applied to the fabricate of the p-GaN HEMT devices.

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Fang, Yi, Ling Chen, Yuqi Liu, and Hong Wang. "Reduction in RF Loss Based on AlGaN Back-Barrier Structure Changes." Micromachines 13, no. 6 (May 26, 2022): 830. http://dx.doi.org/10.3390/mi13060830.

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We designed a high electron mobility transistor (HEMT) epitaxial structure based on an AlGaN/GaN heterojunction, utilizing Silvaco TCAD, and selected AlGaN with an aluminum composition of 0.1 as the back-barrier of the AlGaN/GaN heterojunction. We enhanced the confinement of the two-dimensional electron gas (2DEG) by optimizing the structural parameters of the back barrier, so that the leakage current of the buffer layer is reduced. Through these optimization methods, a lower drain leakage current and a good radio frequency performance were obtained. The device has a cut-off frequency of 48.9 GHz, a maximum oscillation frequency of 73.20 GHz, and a radio frequency loss of 0.239 dB/mm (at 6 GHz). This work provides a basis for the preparation of radio frequency devices with excellent frequency characteristics and low RF loss.

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Bartoš, I., and B. Rosenstein. "Deviations from Quantized Hall Conductivity and Current Density Distribution in Finite 2DEG Samples." International Journal of Modern Physics B 11, no. 22 (September 10, 1997): 2683–706. http://dx.doi.org/10.1142/s0217979297001325.

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Simple expressions for local and total Hall conductivities in finite two dimensional electron systems under magnetic field are obtained from the Kubo formula. The deviations of the Hall conductivity from integer values are always negative and their magnitude is inversely proportional to the effective width of the sample and proportional to the slope of the Landau branch dispersion relation at the Fermi level, Eq. (22). We also calculate the local conductivity in finite samples. The conductivity density is constant in the bulk and sums up to an integer value. Its spatial distribution is terminated in the bulk in a universal manner. Illustrations for simple models of the confinement barrier, as well as relation to recent experimental data for quantum wires are given.

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32

Fauzi, Najihah, Rahil Izzati Mohd Asri, Mohamad Faiz Mohamed Omar, Asrulnizam Abd Manaf, Hiroshi Kawarada, Shaili Falina, and Mohd Syamsul. "Status and Prospects of Heterojunction-Based HEMT for Next-Generation Biosensors." Micromachines 14, no. 2 (January 27, 2023): 325. http://dx.doi.org/10.3390/mi14020325.

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High electron mobility transistor (HEMT) biosensors hold great potential for realizing label-free, real-time, and direct detection. Owing to their unique properties of two-dimensional electron gas (2DEG), HEMT biosensors have the ability to amplify current changes pertinent to potential changes with the introduction of any biomolecules, making them highly surface charge sensitive. This review discusses the recent advances in the use of AlGaN/GaN and AlGaAs/GaAs HEMT as biosensors in the context of different gate architectures. We describe the fundamental mechanisms underlying their operational functions, giving insight into crucial experiments as well as the necessary analysis and validation of data. Surface functionalization and biorecognition integrated into the HEMT gate structures, including self-assembly strategies, are also presented in this review, with relevant and promising applications discussed for ultra-sensitive biosensors. Obstacles and opportunities for possible optimization are also surveyed. Conclusively, future prospects for further development and applications are discussed. This review is instructive for researchers who are new to this field as well as being informative for those who work in related fields.

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Anda, André, Darius Abramavičius, and Thorsten Hansen. "Two-dimensional electronic spectroscopy of anharmonic molecular potentials." Physical Chemistry Chemical Physics 20, no. 3 (2018): 1642–52. http://dx.doi.org/10.1039/c7cp06583c.

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Two-dimensional electronic spectroscopy (2DES) is a powerful tool in the study of coupled electron–phonon dynamics, yet very little is known about how nonlinearities in the electron–phonon coupling, arising from anharmonicities in the nuclear potentials, affect the spectra.

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34

Yashchyshyn, Yevhen, Paweł Bajurko, Jakub Sobolewski, Pavlo Sai, Aleksandra Przewłoka, Aleksandra Krajewska, Paweł Prystawko, et al. "Graphene/AlGaN/GaN RF Switch." Micromachines 12, no. 11 (October 31, 2021): 1343. http://dx.doi.org/10.3390/mi12111343.

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RF switches, which use a combination of graphene and two-dimensional high-density electron gas (2DEG) in the AlGaN/GaN system, were proposed and studied in the frequency band from 10 MHz to 114.5 GHz. The switches were integrated into the coplanar waveguide, which allows them to be used in any system without the use of, e.g., bonding, flip-chip and other technologies and avoiding the matching problems. The on-state insertion losses for the designed switches were measured to range from 7.4 to 19.4 dB, depending on the frequency and switch design. Although, at frequencies above 70 GHz, the switches were less effective, the switching effect was still evident with an approximately 4 dB on–off ratio. The best switches exhibited rise and fall switching times of ~25 ns and ~17 ns, respectively. The use of such a switch can provide up to 20 MHz of bandwidth in time-modulated systems, which is an outstanding result for such systems. The proposed equivalent circuit describes well the switching characteristics and can be used to design switches with required parameters.

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35

Raja, P. Vigneshwara, Nandha Kumar Subramani, Florent Gaillard, Mohamed Bouslama, Raphaël Sommet, and Jean-Christophe Nallatamby. "Identification of Buffer and Surface Traps in Fe-Doped AlGaN/GaN HEMTs Using Y21 Frequency Dispersion Properties." Electronics 10, no. 24 (December 13, 2021): 3096. http://dx.doi.org/10.3390/electronics10243096.

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The buffer and surface trapping effects on low-frequency (LF) Y-parameters of Fe-doped AlGaN/GaN high-electron mobility transistors (HEMTs) are analyzed through experimental and simulation studies. The drain current transient (DCT) characterization is also carried out to complement the trapping investigation. The Y22 and DCT measurements reveal the presence of an electron trap at 0.45–0.5 eV in the HEMT structure. On the other hand, two electron trap states at 0.2 eV and 0.45 eV are identified from the LF Y21 dispersion properties of the same device. The Y-parameter simulations are performed in Sentaurus TCAD in order to detect the spatial location of the traps. As an effective approach, physics-based TCAD models are calibrated by matching the simulated I-V with the measured DC data. The effect of surface donor energy level and trap density on the two-dimensional electron gas (2DEG) density is examined. The validated Y21 simulation results indicate the existence of both acceptor-like traps at EC –0.45 eV in the GaN buffer and surface donor states at EC –0.2 eV in the GaN/nitride interface. Thus, it is shown that LF Y21 characteristics could help in differentiating the defects present in the buffer and surface region, while the DCT and Y22 are mostly sensitive to the buffer traps.

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36

WEIS, JÜRGEN. "Hall Potential Profiles in Quantum Hall Samples Measured by a Low-Temperature Scanning Force Microscope." International Journal of Modern Physics B 21, no. 08n09 (April 10, 2007): 1297–306. http://dx.doi.org/10.1142/s0217979207042768.

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Our measurements of the Hall potential distribution in GaAs/AlGaAs quantum Hall samples using a scanning force microscope at a temperature of 1.4 K are reviewed. The results emphasize the important role of compressible and incompressible strips, running along the edges of the two-dimensional electron system (2DES), for the quantum Hall effect. At the interface line between the 2DES and its alloyed metal contact with good ohmic behavior, a partial depletion of the electron concentration in the 2DES in front of contact is identified, causing for certain magnetic field regimes an incompressible strip lying in parallel to the interface line and therefore isolating the compressible 2DES bulk from the 2DES edge with the contact.

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37

Ye, Tianyu, R. G. Mani, and W. Wegscheider. "Microwave Reflection From The Microwave Photo-Excited High Mobility GaAs/AlGaAs Two-Dimensional Electron System." MRS Proceedings 1617 (2013): 19–24. http://dx.doi.org/10.1557/opl.2013.1158.

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ABSTRACTWe examine the microwave reflection from the high mobility GaAs/AlGaAs two-dimensional electron system (2DES). Strong correlations have been observed between the microwave induced magnetoresistance oscillations and the microwave reflection oscillations in a concurrent measurement of the microwave illuminated magnetoresistance and the microwave reflection from the 2DES. The correlations were followed as a function of the microwave frequency and the microwave power dependent. Different existing theories are considered to explain the results.

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38

Nakata, H., K. Fujii, M. Saitoh, and T. Ohyama. "Photoluminescence of Two-Dimensional Electron System in Modulation-Doped GaAs Quantum Well." International Journal of Modern Physics B 15, no. 28n30 (December 10, 2001): 3897–900. http://dx.doi.org/10.1142/s0217979201008949.

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We have carried out the photoluminescence measurements of two-dimensional electron system (2DES) in modulation-doped GaAs quantum well. It was found that the H band caused by radiative recombination between 2DES and holes shows a high energy tail below 4.2 K. We explain that the tail originates in the apparent breaking of the momentum conservation law, and that its reason is the electron scattering by neutral donors with the Bohr radius of ~10 nm. The distance between the adjacent donors, 80nm, is obtained from the coupling of the Landau levels in the different 2DES's. Excitonic effect is suggested by nonlinear dependence of the peak energy of the H band on magnetic fields and the lineshape analysis of the H band.

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39

Zhang, Penghao, Luyu Wang, Kaiyue Zhu, Qiang Wang, Maolin Pan, Ziqiang Huang, Yannan Yang, et al. "Non-Buffer Epi-AlGaN/GaN on SiC for High-Performance Depletion-Mode MIS-HEMTs Fabrication." Micromachines 14, no. 8 (July 29, 2023): 1523. http://dx.doi.org/10.3390/mi14081523.

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A systematic study of epi-AlGaN/GaN on a SiC substrate was conducted through a comprehensive analysis of material properties and device performance. In this novel epitaxial design, an AlGaN/GaN channel layer was grown directly on the AlN nucleation layer, without the conventional doped thick buffer layer. Compared to the conventional epi-structures on the SiC and Si substrates, the non-buffer epi-AlGaN/GaN structure had a better crystalline quality and surface morphology, with reliable control of growth stress. Hall measurements showed that the novel structure exhibited comparable transport properties to the conventional epi-structure on the SiC substrate, regardless of the buffer layer. Furthermore, almost unchanged carrier distribution from room temperature to 150 °C indicated excellent two-dimensional electron gas (2DEG) confinement due to the pulling effect of the conduction band from the nucleation layer as a back-barrier. High-performance depletion-mode MIS-HEMTs were demonstrated with on-resistance of 5.84 Ω·mm and an output current of 1002 mA/mm. The dynamic characteristics showed a much smaller decrease in the saturation current (only ~7%), with a quiescent drain bias of 40 V, which was strong evidence of less electron trapping owing to the high-quality non-buffer AlGaN/GaN epitaxial growth.

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Ye, Tianyu, Ramesh Mani, and Werner Wegscheider. "Microwave reflection study of ultra-high mobility GaAs/AlGaAs 2D-electron system at large filling factors." MRS Proceedings 1635 (2014): 69–74. http://dx.doi.org/10.1557/opl.2014.107.

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ABSTRACTThe microwave-induced magnetoresistance oscillations are exhibited by the GaAs/AlGaAs two dimensional electron system (2DES) under microwave and terahertz photo-excitation at liquid helium temperatures. Such oscillations are presently understood in terms of various theories. In order to identify the relative physical contributions, we have concurrently examined magnetotransport and microwave reflection from the 2DES. For the reflection measurements, a sensitive microwave detector was assimilated into the standard experimental setup. Here, we correlate changes in reflection with the concurrent transport response of the photo-excited 2DES.

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41

Patrizi, Barbara, Concetta Cozza, Adriana Pietropaolo, Paolo Foggi, and Mario Siciliani de Cumis. "Synergistic Approach of Ultrafast Spectroscopy and Molecular Simulations in the Characterization of Intramolecular Charge Transfer in Push-Pull Molecules." Molecules 25, no. 2 (January 20, 2020): 430. http://dx.doi.org/10.3390/molecules25020430.

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The comprehensive characterization of Intramolecular Charge Transfer (ICT) stemming in push-pull molecules with a delocalized π-system of electrons is noteworthy for a bespoke design of organic materials, spanning widespread applications from photovoltaics to nanomedicine imaging devices. Photo-induced ICT is characterized by structural reorganizations, which allows the molecule to adapt to the new electronic density distribution. Herein, we discuss recent photophysical advances combined with recent progresses in the computational chemistry of photoactive molecular ensembles. We focus the discussion on femtosecond Transient Absorption Spectroscopy (TAS) enabling us to follow the transition from a Locally Excited (LE) state to the ICT and to understand how the environment polarity influences radiative and non-radiative decay mechanisms. In many cases, the charge transfer transition is accompanied by structural rearrangements, such as the twisting or molecule planarization. The possibility of an accurate prediction of the charge-transfer occurring in complex molecules and molecular materials represents an enormous advantage in guiding new molecular and materials design. We briefly report on recent advances in ultrafast multidimensional spectroscopy, in particular, Two-Dimensional Electronic Spectroscopy (2DES), in unraveling the ICT nature of push-pull molecular systems. A theoretical description at the atomistic level of photo-induced molecular transitions can predict with reasonable accuracy the properties of photoactive molecules. In this framework, the review includes a discussion on the advances from simulation and modeling, which have provided, over the years, significant information on photoexcitation, emission, charge-transport, and decay pathways. Density Functional Theory (DFT) coupled with the Time-Dependent (TD) framework can describe electronic properties and dynamics for a limited system size. More recently, Machine Learning (ML) or deep learning approaches, as well as free-energy simulations containing excited state potentials, can speed up the calculations with transferable accuracy to more complex molecules with extended system size. A perspective on combining ultrafast spectroscopy with molecular simulations is foreseen for optimizing the design of photoactive compounds with tunable properties.

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Wang, Hongyue, Yijun Shi, Yajie Xin, Chang Liu, Guoguang Lu, and Yun Huang. "Improving Breakdown Voltage and Threshold Voltage Stability by Clamping Channel Potential for Short-Channel Power p-GaN HEMTs." Micromachines 13, no. 2 (January 25, 2022): 176. http://dx.doi.org/10.3390/mi13020176.

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This paper proposes a novel p-GaN HEMT (P-HEMT) by clamping channel potential to improve breakdown voltage (BV) and threshold voltage (VTH) stability. The clamping channel potential for P-HEMT is achieved by a partially-recessed p-GaN layer (PR p-GaN layer). At high drain bias, the two-dimensional electron gas (2DEG) channel under the PR p-GaN layer is depleted to withstand the drain bias. Therefore, the channel potential at the drain-side of the p-GaN layer is clamped to improve BV and VTH stability. Compared with the conventional p-GaN HEMT (C-HEMT), simulation results show that the BV is improved by 120%, and the VTH stability induced by high drain bias is increased by 490% for the same on-resistance. In addition, the influence of the PR p-GaN layers’ length, thickness, doping density on BV and VTH stability is analyzed. The proposed device can be a good reference to improve breakdown voltage and threshold voltage stability for short-channel power p-GaN HEMTs.

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CHEN, YONG P., Z. H. WANG, R. M. LEWIS, P. D. YE, L. W. ENGEL, D. C. TSUI, L. N. PFEIFFER, and K. W. WEST. "AC MAGNETOTRANSPORT IN REENTRANT INSULATING PHASES OF TWO-DIMENSIONAL ELECTRONS NEAR 1/5 AND 1/3 LANDAU FILLINGS." International Journal of Modern Physics B 18, no. 27n29 (November 30, 2004): 3553–56. http://dx.doi.org/10.1142/s0217979204027001.

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We have measured high frequency magnetotransport of a high quality two-dimensional electron system (2DES) near the reentrant insulating phase (RIP) at Landau fillings (ν) between 1/5 and 2/9. The magnetoconductivity in the RIP has resonant behavior around 150 MHz, showing a peak at ν~0.21. Our data support the interpretation of the RIP as due to some pinned electron solid. We have also investigated a narrowly confined 2DES recently found to have a RIP at 1/3<ν<1/2 and we have revealed features, not seen in DC transport, that suggest some intriguing interplay between the 1/3 FQHE and RIP.

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De Sio, Antonietta, Xuan Trung Nguyen, and Christoph Lienau. "Signatures of Strong Vibronic Coupling Mediating Coherent Charge Transfer in Two-Dimensional Electronic Spectroscopy." Zeitschrift für Naturforschung A 74, no. 8 (August 27, 2019): 721–37. http://dx.doi.org/10.1515/zna-2019-0150.

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AbstractThe role of molecular vibrations for the persistence of quantum coherences, recently observed in photoinduced charge transfer reactions in both biological and artificial energy conversion systems at room temperature, is currently being intensely discussed. Experiments using two-dimensional electronic spectroscopy (2DES) suggest that vibrational motion – and its coupling to electronic degrees of freedom – may play a key role for such coherent dynamics and potentially even for device function. In organic photovoltaics materials, strong coupling of electronic and vibrational motion is predicted, especially for ubiquitous C=C stretching vibrations. The signatures of such strong vibronic couplings in 2DES are, however, debated. Here we analyse the effect of strong vibronic coupling in model simulations of 2DES spectra and dynamics for an electronic dimer coupled to a single high-frequency vibrational mode. This system represents the simplest conceivable model for a prototypical donor–acceptor interface in the active layer of organic solar cells. The vibrational mode is chosen to mimic C=C stretching vibrations with typical large vibronic couplings predicted in organic photovoltaics materials. Our results show that the decisive signatures of strong vibronic coupling mediating coherent charge transfer between donor and acceptor are not only temporally oscillating cross-peaks, but also most importantly characteristic peak splittings in the 2DES spectra. The 2DES pattern thus directly reflects the new eigenstates of the system that are formed by strong mixing of electronic states and vibrational mode.

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Anna, Jessica M., Yin Song, Rayomond Dinshaw, and Gregory D. Scholes. "Two-dimensional electronic spectroscopy for mapping molecular photophysics." Pure and Applied Chemistry 85, no. 7 (April 26, 2013): 1307–19. http://dx.doi.org/10.1351/pac-con-12-10-21.

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We demonstrate the ability of two-dimensional electronic spectroscopy (2DES) to map ultrafast energy transfer and dynamics in two systems: the pigment–protein complex photosystem I (PSI) and aggregates of the conjugated polymer poly(3-hexylthiophene) (P3HT). A detailed description of our experimental set-up and data processing procedure is also given.

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Nanayakkara, T. R., R. L. Samaraweera, A. Kriisa, U. Kushan Wijewardena, S. Withanage, C. Reichl, W. Wegscheider, and R. G. Mani. "Influence of microwave photo-excitation on the transport properties of the high mobility GaAs/AlGaAs 2D electron system." MRS Advances 4, no. 61-62 (2019): 3347–52. http://dx.doi.org/10.1557/adv.2020.30.

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ABSTRACTWe examined the influence of the microwave power on the diagonal resistance in the GaAs/AlGaAs two dimensional electron system (2DES), in order to extract the electron temperature and determine microwave induced heating as a function of the microwave power. The study shows that microwaves produce a small discernable increase in the electron temperature both at null magnetic field and at finite magnetic fields in the GaAs/AlGaAs 2DES. The heating effect at null field appears greater in comparison to the examined finite field interval, although the increase in the electron temperature in the zero-field limit appears smaller than theoretical predictions.

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Wang, Haiping, Haifan You, Jiangui Yang, Minqiang Yang, Lu Wang, Hong Zhao, Zili Xie, and Dunjun Chen. "Simulation Study on the Structure Design of p-GaN/AlGaN/GaN HEMT-Based Ultraviolet Phototransistors." Micromachines 13, no. 12 (December 13, 2022): 2210. http://dx.doi.org/10.3390/mi13122210.

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This work investigates the impacts of structural parameters on the performances of p-GaN/AlGaN/GaN HEMT-based ultraviolet (UV) phototransistors (PTs) using Silvaco Atlas. The simulation results show that a larger Al content or greater thickness for the AlGaN barrier layer can induce a higher two-dimensional electron gas (2DEG) density and produce a larger photocurrent. However, they may also lead to a larger dark current due to the incomplete depletion of the GaN channel layer. The depletion conditions with various Al contents and thicknesses of the AlGaN layer are investigated in detail, and a borderline between full depletion and incomplete depletion was drawn. An optimized structure with an Al content of 0.23 and a thickness of 14 nm is achieved for UV-PT, which exhibits a high photocurrent density of 92.11 mA/mm, a low dark current density of 7.68 × 10−10 mA/mm, and a large photo-to-dark-current ratio of over 1011 at a drain voltage of 5 V. In addition, the effects of other structural parameters, such as the thickness and hole concentration of the p-GaN layer as well as the thickness of the GaN channel layer, on the performances of the UV-PTs are also studied in this work.

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Sun, Youlei, Ying Wang, Jianxiang Tang, Wenju Wang, Yifei Huang, and Xiaofei Kuang. "A Breakdown Enhanced AlGaN/GaN Schottky Barrier Diode with the T-Anode Position Deep into the Bottom Buffer Layer." Micromachines 10, no. 2 (January 26, 2019): 91. http://dx.doi.org/10.3390/mi10020091.

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In this paper, an AlGaN/GaN Schottky barrier diode (SBD) with the T-anode located deep into the bottom buffer layer in combination with field plates (TAI-BBF FPs SBD) is proposed. The electrical characteristics of the proposed structure and the conventional AlGaN/GaN SBD with gated edge termination (GET SBD) were simulated and compared using a Technology Computer Aided Design (TCAD) tool. The results proved that the breakdown voltage (VBK) in the proposed structure was tremendously improved when compared to the GET SBD. This enhancement is attributed to the suppression of the anode tunneling current by the T-anode and the redistribution of the electric field in the anode–cathode region induced by the field plates (FPs). Moreover, the T-anode had a negligible effect on the two-dimensional electron gas (2DEG) in the channel layer, so there is no deterioration in the forward characteristics. After being optimized, the proposed structure exhibited a low turn-on voltage (VT) of 0.53 V and a specific on-resistance (RON,sp) of 0.32 mΩ·cm2, which was similar to the GET SBD. Meanwhile, the TAI-BBF FP SBD with an anode-cathode spacing of 5 μm achieved a VBK of 1252 V, which was enhanced almost six times compared to the GET SBD with a VBK of 213 V.

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TAKEHANA, K., Y. IMANAKA, T. TAKAMASU, and M. HENINI. "INFLUENCE OF NEARBY QD LAYER ON 2DES IN QUANTUM HALL REGIME." International Journal of Modern Physics B 21, no. 08n09 (April 10, 2007): 1445–49. http://dx.doi.org/10.1142/s0217979207042987.

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We have investigated transport properties in high magnetic field of a gated two-dimensional electron system (2DES) separated by a thin barrier from a layer of self-assembled InAs quantum dots (QDs) in the quantum Hall regime. The quality of 2DES was found to be high enough to observe both integer and fractional quantum Hall effect (QHE), despite the proximity of the QD layer to the 2DES. However, significant suppression of the magnetoresistance (ρ xx ) and Hall resistance (ρ xy ) were observed in higher magnetic field range of filling factor ν < 1 when a positive voltage was applied to the front gate. The gate voltage dependence of ρ xx and ρ xy shows a well-defined hysteresis loop at the narrow gate voltage range between -0.2 and +0.2 V at ν < 1, while no anomaly was observed at ν > 1. We deduce that charging and discharging of QDs occurs when the gate voltage is varied around Vg ~ 0 V, which indicates that the electron charge states of the QDs affect the transport properties of the nearby 2DES only at ν < 1. We infer that the spin-flip process induces a non-equilibrium state in the 2DEG, which causes the suppression of ρ xx and ρ xy .

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Takaoka, Sadao, Kenichi Oto, and Kazuo Murase. "Magnetocapacitance Investigation of Quantum Hall Effect and Edge States." International Journal of Modern Physics B 11, no. 22 (September 10, 1997): 2593–619. http://dx.doi.org/10.1142/s0217979297001295.

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Abstract:

The quantum Hall effect for the GaAs/AlGaAs heterostrcture is investigated by an ac capacitance measurement between the two-dimensional electron system (2DES) and the gate on GaAs/AlGaAs. The capacitance minima at the quantum Hall plateaus are mainly determined not by the 2DES area under the gate but by the edge length of 2DES. There exists the high conductive region due to the edge states along the 2DES boundary, when the bulk conductivity σxx is small enough at low temperatures and high magnetic fields. From the temperature and frequency dependence of the capacitance minima, it is found that the measured capacitance consists of the contribution from the edge states and that of the bulk state, which is treated as a distributed circuit of a resistive plate with the conductivity σxx. The evaluated width of edge states from the capacitance is much larger than the magnetic length and the cyclotron radius expected from the one-electron picture. This wide width of edge states can be explained by the compressible-incompressible strip model, in which the screening effect is taken into account. Further the bulk conductivity of less than 10-12 S (S=1/Ω) is measured by the capacitance of the Corbino geometry sample, where the edge states are absent and the capacitance is determined by only σxx in this geometry. The localization of the bulk state is investigated by the obtained σxx.

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Journal articles on the topic 'Two Dimensional Electron Systems (2DES)'

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