Journal articles: 'Two Dimensional Electron Gas System (2DEG)'

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Shimizu, Sunao, Mohammad Saeed Bahramy, Takahiko Iizuka, Shimpei Ono, Kazumoto Miwa, Yoshinori Tokura, and Yoshihiro Iwasa. "Enhanced thermopower in ZnO two-dimensional electron gas." Proceedings of the National Academy of Sciences 113, no. 23 (May 24, 2016): 6438–43. http://dx.doi.org/10.1073/pnas.1525500113.

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Control of dimensionality has proven to be an effective way to manipulate the electronic properties of materials, thereby enabling exotic quantum phenomena, such as superconductivity, quantum Hall effects, and valleytronic effects. Another example is thermoelectricity, which has been theoretically proposed to be favorably controllable by reducing the dimensionality. Here, we verify this proposal by performing a systematic study on a gate-tuned 2D electron gas (2DEG) system formed at the surface of ZnO. Combining state-of-the-art electric-double-layer transistor experiments and realistic tight-binding calculations, we show that, for a wide range of carrier densities, the 2DEG channel comprises a single subband, and its effective thickness can be reduced to ∼ 1 nm at sufficiently high gate biases. We also demonstrate that the thermoelectric performance of the 2DEG region is significantly higher than that of bulk ZnO. Our approach opens up a route to exploit the peculiar behavior of 2DEG electronic states and realize thermoelectric devices with advanced functionalities.

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Najafi, M. N., S. Tizdast, Z. Moghaddam, and M. Samadpour. "Flicker noise in two-dimensional electron gas." Physica Scripta 96, no. 12 (November 30, 2021): 125259. http://dx.doi.org/10.1088/1402-4896/ac3c11.

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Abstract Using the method developed in a recent paper (2019 Euro. Phys. J. B 92 1–28) we consider 1/f noise in two-dimensional electron gas (2DEG). The electron coherence length of the system is considered as a basic parameter for discretizing the space, inside which the dynamics of electrons is described by quantum mechanics, while for length scales much larger than it the dynamics is semi-classical. For our model, which is based on the Thomas-Fermi–Dirac approximation, there are two control parameters: temperature T and the disorder strength (Δ). Our Monte Carlo studies show that the system exhibits 1/f noise related to the electronic avalanche size, which can serve as a model for describing the experimentally observed flicker noise in 2DEG. The power spectrum of our model scales with the frequency with an exponent in the interval 0.3 < α PS < 0.6. We numerically show that the electronic avalanches are scale-invariant with power-law behaviors in and out of the metal-insulator transition line.

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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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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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Xu, W., and C. Zhang. "Electrical Generation of Spontaneous Optical Emission in Electrically Modulated Two-Dimensional Electron Gases at Low-Temperatures." International Journal of Modern Physics B 12, no. 05 (February 20, 1998): 579–90. http://dx.doi.org/10.1142/s021797929800034x.

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A detailed theoretical study is presented for spontaneous optical emission from a two-dimensional electron gas (2DEG) in the presence of a unidirectional spatially periodic modulation at low temperatures. The momentum- and energy-balance equations for electron–photon interactions in the device system are solved self-consistently using the Boltzmann equation, from which we can obtain the frequency and the intensity of the electromagnetic radiation generated. The results obtained indicate that: (1) in an electrically modulated 2DEG at low temperatures, a strong electromagnetic radiation emission up to W/cm2 can be generated by applying a small d.c. electric field; (2) the radiation emission is generated indirectly in the occupied subbands through electronic transitions around the Fermi level; (3) the frequency of the radiation generated is at about 0.1 THz; (4) in the low frequency regime, spontaneous multiphoton emissions can be observed; and (5) this type of optical emission depends strongly on the sample parameters such as the electron density of the 2DEG and the modulation length.

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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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Bhattacharya, Sanchari, Soumyasree Jena, and Sanjoy Datta. "Emergent Phenomena in KTaO₃/SrTiO₃ Heterostructure." Journal of Physics: Conference Series 2518, no. 1 (June 1, 2023): 012019. http://dx.doi.org/10.1088/1742-6596/2518/1/012019.

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Abstract KTaO3 has become a new material of attraction for exploring various exotic properties at its surface and interfaces. To explore the substrate effect of KTaO3, we have studied a new heterostructure made by KTaO3 and SrTiO3. KTaO3 is a 5d polar perovskite with the complementary planes of KO− and TaO 2 + , whereas SrTiO3 is a 3d non-polar perovskite with alternative stacking SrO0 and TiO 2 0 . By taking the epitaxial layers of SrTiO3 on top of KTaO3, we have created two different interfaces along (0 0 1), which are KO − / TiO 2 0 and TaO 2 + / SrO 0 . We have studied these two interfaces by using density functional theory. In KO − / TiO 2 0 interface, the signature of two-dimensional hole gas (2DHG) has been found. Though the interface turns to insulator when epitaxial layers reach beyond 4.5 u.c. The other one, i.e., TaO 2 + / SrO 0 interface, shows the typical behaviour of two-dimensional electron gas (2DEG), only at the epitaxial layer 2.5 uc. The presence of both types of carriers in a single system for different kinds of interfaces has great use in various device applications.

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Чумаков, Н. К., И. А. Черных, A. Б. Давыдов, И. С. Езубченко, Ю. В. Грищенко, Л. Л. Лев, И. О. Майборода, et al. "Квантовая когерентность и эффект Кондо в двумерном электронном газе магнитно-нелегированных гетероструктур AlGaN/GaN." Физика и техника полупроводников 54, no. 9 (2020): 962. http://dx.doi.org/10.21883/ftp.2020.09.49840.34.

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Abstract The unusual observation of the Kondo effect in the two-dimensional electron gas (2DEG) of magnetically undoped AlGaN/GaN heterostructures is reported. The temperature-dependent zero-field resistivity data exhibits an upturn below 120 K, while the standard low-temperature weak localization and then weak antilocalization behaviour is revealed at T → 0. Magnetic transport investigations of the system are performed in the temperature range of 0.1–300 K and at magnetic fields up to 8 T, applied perpendicularly to the 2DEG plane. The experimental data are analyzed in terms of the multichannel Kondo model for d _0 magnetic materials and weak localization theory taking into account the spin-orbit interaction.

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Shih, Chien-Fu, Liann-Be Chang, Ming-Jer Jeng, Yu-Li Hsieh, Ying-Chang Li, and Zi-Xin Ding. "GaN 2DEG Varactor-Based Impulse Suppression Module for Protection Against Malicious Electromagnetic Interference." Journal of Electronic Materials 49, no. 11 (April 10, 2020): 6798–805. http://dx.doi.org/10.1007/s11664-020-08110-0.

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Abstract A GaN-based metal–semiconductor–metal varactor with a two-dimensional electron gas (2DEG) layer is proposed and fabricated. The capacitance variation of this fabricated varactor biased at different external voltages is studied and measured, and the frequency-dependent capacitance and resistance of the varactor are simulated by a corresponding empirical formula. A high-frequency protective filter is further constructed and placed under a large pulsed-current injection in a malicious electromagnetic interference immunity test. The results show that the proposed GaN-based module can reduce the large pulsed current to an acceptably small level. Thus, the GaN-based 2DEG varactor is an attractive candidate for applications designed to protect the upcoming 5G high-frequency system from risks such as electrostatic discharge, lightning, and electromagnetic pulses.

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Muraguchi, Masakazu, Yoko Sakurai, Yukihiro Takada, Yasuteru Shigeta, Mitsuhisa Ikeda, Katsunori Makihara, Seiichi Miyazaki, Shintaro Nomura, Kenji Shiraishi, and Tetsuo Endoh. "Collective Electron Tunneling Model in Si-Nano Dot Floating Gate MOS Structure." Key Engineering Materials 470 (February 2011): 48–53. http://dx.doi.org/10.4028/www.scientific.net/kem.470.48.

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We study the sweep speed dependence of electron injection voltage in Si-Nano-Dots (Si-NDs) floating gate MOS Capacitor by using our collective tunneling model, which models the tunneling between two-dimensional electron gas (2DEG) and the Si-NDs. We clarify the sweep speed dependence of electron injection energy with a numerical calculation based on our collective tunneling model, that we developed to emulate the experiment in this system, and obtained a new insight into the origin of sweep speed dependence. We revealed that our model can reproduce the sweep speed dependence of electron tunneling. This insight is useful for designing future nano-electronic devices.

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Kumar, Avinash, and Uttam Singisetti. "Full-band Monte Carlo simulation of two-dimensional electron gas in (Al_xGa_1−x)₂O₃/Ga₂O₃ heterostructures." Journal of Applied Physics 132, no. 20 (November 28, 2022): 205701. http://dx.doi.org/10.1063/5.0109577.

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[Formula: see text]-Gallium oxide (Ga[Formula: see text]O[Formula: see text]) is an extensively investigated ultrawide-bandgap semiconductor for potential applications in power electronics and radio frequency switching. The room temperature bulk electron mobility ([Formula: see text]) is comparatively low and is limited by the 30 phonon modes originating from its 10-atom primitive cell. The theoretically calculated saturation velocity in bulk is 1–[Formula: see text] (comparable to GaN) and is limited by the low field mobility. This work explores the high field electron transport (and hence the velocity saturation) in the 2DEG based on the first principles calculated parameters. A self-consistent calculation on a given heterostructure design gives the confined eigenfunctions and eigenenergies. The intrasubband and the intersubband scattering rates are calculated based on the Fermi’s golden rule considering longitudinal optical (LO) phonon–plasmon screening. The high field characteristics are extracted from the full-band Monte Carlo simulation of heterostructures at 300 K. The overall system is divided into a 2D and a 3D region mimicking the electrons in the 2DEG and the bulk, respectively. The electron transport is treated through an integrated Monte Carlo program which outputs the steady state zone population, transient dynamics, and the velocity–field curves for a few heterostructure designs. The critical field for saturation does not change significantly from bulk values, however, an improved peak velocity is calculated at a higher 2DEG density. The velocity at low 2DEG densities is impacted by the antiscreening of LO phonons which plays an important role in shaping the zone population. A comparison with the experimental measurements is also carried out and possible origins of the discrepancies with experiments is discussed.

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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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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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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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Kaur, Amandeep, Kousik Bera, Santosh Kumar Yadav, S. M. Shivaprasad, Anushree Roy, and Subhabrata Dhar. "Understanding the origin of mobility enhancement in wedge-shaped c-GaN nanowall networks utilizing spectroscopic techniques." Journal of Applied Physics 132, no. 19 (November 21, 2022): 194305. http://dx.doi.org/10.1063/5.0122101.

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Recently, the electron mobility in wedge-shaped c-GaN nanowall networks has been estimated to cross the theoretical mobility limit for bulk GaN. Significant blue-shift of the bandgap has also been observed. Both the findings are explained in terms of two-dimensional electron gas (2DEG) formed at the central vertical plane of the walls due to the polarization charges at the two inclined faces. Carrier concentration and mobility have earlier been determined from thermoelectric power and conductivity measurements with the help of a statistical model. Due to the network nature of the system, direct measurements of these quantities from Hall experiments are not possible. Search for a better way to estimate mobility in this system thus becomes important. Since, strain can also lead to the blue-shift of the bandgap, it is also imperative to evaluate carefully the role of strain. Here, using Raman spectroscopy, we have estimated carrier concentration and mobility in these nanowall networks with varied average tip-widths. Depth distribution of strain and luminescence characteristics are also studied. The study reveals that strain has no role in the bandgap enhancement. Moreover, the electron mobility, which is determined from the lineshape analysis of the A1(LO)-plasmon coupled mode in Raman spectra, has been found to be significantly higher than the theoretical limit of mobility for bulk GaN for the same electron concentration. These results thus corroborate the picture of polarization induced vertical 2DEG formation in these walls as predicted theoretically.

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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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Huang, Angus, Sheng-Hsiung Hung, and Horng-Tay Jeng. "Strain Induced Metal–Insulator Transition of Magnetic SrRuO3 Single Layer in SrRuO3/SrTiO3 Superlattice." Applied Sciences 8, no. 11 (November 3, 2018): 2151. http://dx.doi.org/10.3390/app8112151.

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Ferromagnetic phase in a two-dimensional system plays an important role not only in applications but also in studies of phase transition theory. Among numerous ferromagnetic materials, Sr Ru O 3 is famous for its half-metallicity, itinerant ferromagnetism and non-Fermi liquid metalicity. Single layer Sr Ru O 3 in Sr Ru O 3 / Sr Ti O 3 (SRO/STO) superlattice has been predicted as a two-dimensional half-metallic ferromagnetic system based on density functional theory (DFT). However, experiments show that metal–insulator transition associated with ferro–antiferromagnetism (FM–AFM) transition occurs when the thickness of SRO is less than 4 u.c. Combining DFT calculations with Monte Carlo simulations, we demonstrate in this work that the bulk ferromagnetic metallicity can be realized in single layer SRO in SRO/STO superlattice by manipulating the strain effect to trigger the metal–insulator transition, achieving two-dimensional (2D) half-metallic SRO thin film beyond the experimental observation of AFM insulator.Our results pave a new route to fulfill the ultrathin spin-polarized-2D electron gas (SP-2DEG).

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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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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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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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Li, J. Z., J. Li, J. Y. Lin, and H. X. Jiang. "Correlation Between Sheet Carrier Density-Mobility Product and Persistent Photoconductivity in AlGaN/GaN Modulation Doped Heterostructures." MRS Internet Journal of Nitride Semiconductor Research 5, S1 (2000): 626–32. http://dx.doi.org/10.1557/s1092578300004853.

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High quality Al0.25Ga0.75N/GaN modulation-doped heterojunction field-effect transistor (MOD-HFET) structures grown on sapphire substrates with high sheet carrier density and mobility products (nsμ > 1016/Vs at room temperature) have been grown by metal organic chemical vapor deposition (MOCVD). The optimized structures were achieved by varying structural parameters, including the AlGaN spacer layer thickness, the Si-doped AlGaN barrier layer thickness, the Si-doping concentration, and the growth pressure. In these structures, the persistent photoconductivity (PPC) effect associated with the two-dimensional electron gas (2DEG) system was invariantly observed. As a consequence, the characteristic parameters of the 2DEG were sensitive to light and the sensitivity was associated with permanent photoinduced increases in the 2DEG carrier mobility (μ) and sheet carrier density (ns). However, we observed that the magnitude of the PPC and hence the photoinduced instability associated with these heterostructures were a strong function of only one parameter, the product of ns and μ, which is the most important parameter for the HFET device design. For a fixed excitation photon dose, the ratio of the low temperature PPC to the dark conductivity level was observed to decrease from 200% to 3% as the nsμ (300 K) product was increased from 0.048 × 1016/Vs to 1.4 × 1016/Vs. Based on our studies, we suggest that the magnitude of the low temperature PPC can be used as a sensitive probe for monitoring the electronic quality of the AlGaN/GaN HFET structures.

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Chen, Zhesheng, Jelena Sjakste, Jingwei Dong, Amina Taleb-Ibrahimi, Jean-Pascal Rueff, Abhay Shukla, Jacques Peretti, Evangelos Papalazarou, Marino Marsi, and Luca Perfetti. "Ultrafast dynamics of hot carriers in a quasi–two-dimensional electron gas on InSe." Proceedings of the National Academy of Sciences 117, no. 36 (August 26, 2020): 21962–67. http://dx.doi.org/10.1073/pnas.2008282117.

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Two-dimensional electron gases (2DEGs) are at the base of current nanoelectronics because of their exceptional mobilities. Often the accumulation layer forms at polar interfaces with longitudinal optical (LO) modes. In most cases, the many-body screening of the quasi-2DEGs dramatically reduces the Fröhlich scattering strength. Despite the effectiveness of such a process, it has been recurrently proposed that a remote coupling with LO phonons persists even at high carrier concentration. We address this issue by perturbing electrons in an accumulation layer via an ultrafast laser pulse and monitoring their relaxation via time- and momentum-resolved spectroscopy. The cooling rate of excited carriers is monitored at doping level spanning from the semiconducting to the metallic limit. We observe that screening of LO phonons is not as efficient as it would be in a strictly 2D system. The large discrepancy is due to the remote coupling of confined states with the bulk. Our data indicate that the effect of such a remote coupling can be mimicked by a 3D Fröhlich interaction with Thomas–Fermi screening. These conclusions are very general and should apply to field effect transistors (FET) with high-κ dielectric gates, van der Waals heterostructures, and metallic interfaces between insulating oxides.

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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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XIA, J. S., E. D. ADAMS, N. S. SULLIVAN, W. PAN, H. L. STORMER, and D. C. TSUI. "SAMPLE COOLING AND ROTATION AT ULTRA-LOW TEMPERATURES AND HIGH MAGNETIC FIELDS." International Journal of Modern Physics B 16, no. 20n22 (August 30, 2002): 2986–89. http://dx.doi.org/10.1142/s0217979202013390.

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A rotator, made from polycarbonate and operated hydraulically using liquid helium, has been developed at the High B/T Facility of the National High Magnetic Field Laboratory (NHMFL) in Gainesville, It can be tilted more than 90 degrees by applying a pressure of several bars. The frictional heating was found to be negligible down to 8.0 mK. The sintered silver powder heat exchangers, specially designed for the cooling of the two-dimensional electron gas (2DEG) system in the fractional quantum Hall effect (FQHE) experiment,1,2 are also attached to the rotator. We have conducted an angular-dependent study of the even-denominator FQHE state at ν = 5/2. Our preliminary data showed that the rotator performed well at ultra-low temperatures and high magnetic fields. This technique should be applicable for other transport measurements at such extreme experimental conditions.

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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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MAHFOUZI, FARZAD, and BRANISLAV K. NIKOLIĆ. "HOW TO CONSTRUCT THE PROPER GAUGE-INVARIANT DENSITY MATRIX IN STEADY-STATE NONEQUILIBRIUM: APPLICATIONS TO SPIN-TRANSFER AND SPIN-ORBIT TORQUES." SPIN 03, no. 02 (June 2013): 1330002. http://dx.doi.org/10.1142/s2010324713300028.

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Experiments observing spin density and spin currents (responsible for, e.g., spin-transfer torque) in spintronic devices measure only the nonequilibrium contributions to these quantities, typically driven by injecting unpolarized charge current or by applying external time-dependent fields. On the other hand, theoretical approaches to calculate these quantities operate with both the nonequilibrium (carried by electrons around the Fermi surface) and the equilibrium (carried by the Fermi sea electrons) contributions to them. Thus, an unambiguous procedure should remove the equilibrium contributions, thereby rendering the nonequilibrium ones which are measurable and satisfy the gauge-invariant condition according to which expectation values of physical quantities should not change when electric potential everywhere is shifted by a constant amount. Using the framework of nonequilibrium Green functions, we delineate such procedure which yields the proper gauge-invariant nonequilibrium density matrix in the linear-response and elastic transport regime for current-carrying steady state of an open quantum system connected to two macroscopic reservoirs. Its usage is illustrated by computing: (i) conventional spin-transfer torque (STT) in asymmetric F/I/F magnetic tunnel junctions (MTJs); (ii) unconventional STT in asymmetric N/I/F semi-MTJs with the strong Rashba spin–orbit coupling (SOC) at the I/F interface and injected current perpendicular to that plane; and (iii) current-driven spin density within a clean ferromagnetic Rashba spin-split two-dimensional electron gas (2DEG) which generates SO torque in laterally patterned N/F/I heterostructures when such 2DEG is located at the N/F interface and injected charge current flows parallel to the plane. We also compare our results for these three examples with those that would be obtained using improper expressions for the density matrix, which are often found in the literature but which arbitrarily mix nonequilibrium and equilibrium expectation values due to a violation of the gauge invariance.

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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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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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DIDUCK, QUENTIN, HIROSHI IRIE, and MARTIN MARGALA. "A ROOM TEMPERATURE BALLISTIC DEFLECTION TRANSISTOR FOR HIGH PERFORMANCE APPLICATIONS." International Journal of High Speed Electronics and Systems 19, no. 01 (March 2009): 23–31. http://dx.doi.org/10.1142/s0129156409006060.

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The Ballistic Deflection Transistor (BDT) is a novel device that is based upon an electron steering and a ballistic deflection effect. Composed of an InGaAs - InAlAs heterostructure on an InP substrate, this material system provides a large mean free path and high mobility to support ballistic transport at room temperature. The planar nature of the device enables a two step lithography process, as well, implies a very low capacitance design. This transistor is unique in that no doping junction or barrier structure is employed. Rather, the transistor utilizes a two-dimensional electron gas (2DEG) to achieve ballistic electron transport in a gated microstructure, combined with asymmetric geometrical deflection. Motivated by reduced transit times, the structure can be operated such that current never stops flowing, but rather is only directed toward one of two output drain terminals. The BDT is unique in that it possesses both a positive and negative transconductance region. Experimental measurements have indicated that the transconductance of the device increases with applied drain-source voltage. DC measurements of prototype devices have verified small signal voltage gains of over 150, with transconductance values from 45 to 130 mS/mm depending upon geometry and bias. Gate-channel separation is currently 80nm, and allows for higher transconductance through scaling. The six terminal device enables a normally differential mode of operation, and provides two drain outputs. These outputs, depending on gate bias, are either complementary or non-complementary. This facilitates a wide variety of circuit design techniques. Given the ultralow capacitive design, initial estimates of ft, for the device fabricated with a 430nm gate width, are over a THz.

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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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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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Zhang, Peng, Patrick Wong, Yang Zhou, John D. Albrecht, Matt Hodek, and David Smithe. "Space charge waves in a two-dimensional electron gas." Journal of Applied Physics 131, no. 14 (April 14, 2022): 144302. http://dx.doi.org/10.1063/5.0085104.

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This paper uses field theory to derive the exact dispersion relation of space charge waves in a two-dimensional electron gas (2DEG) located in a dielectric or a dissimilar dielectric waveguide. It is found that the dispersion of a 2DEG can be modeled accurately using the free-electron sheet model, which is further confirmed by the almost identical polarizability of a 2DEG and of a free-electron sheet with zero drift velocity. Transitions among the well-known 2DEG dispersion, the beam mode in vacuum electronics, and Gould–Trivelpiece mode in plasma physics are demonstrated by varying the 2DEG density and direct current drift velocity. The effects of waveguide dimensions are also presented. Our method is general and can be applied to find the dispersion relation of 2DEG with arbitrary drift velocity (governed by electric field and scattering) in more complex circuits. Our study provides insight into the design of electromagnetic wave devices and circuits involving a 2DEG.

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ASHKINADZE, B. M., E. LINDER, E. COHEN, and L. N. PFEIFFER. "MICROWAVE-MODULATED PHOTOLUMINESCENCE OF A TWO-DIMENSIONAL ELECTRON GAS." International Journal of Modern Physics B 21, no. 08n09 (April 10, 2007): 1541–48. http://dx.doi.org/10.1142/s0217979207043166.

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The primary effect of microwave (mw) irradiation on a two dimensional electron gas (2DEG) is heating due to mw absorption by the electrons. At low lattice temperatures, pronounced secondary effects are observed: mw-induced modification of the photoluminescence (PL) spectrum and mw-induced resistance oscillations (MIRO). We present an experimental study of mw-modulated PL (MPL) spectroscopy in modulation-doped GaAs/AlGaAs QW's At low magnetic field strengths (B < 0.5 T ), the analysis of the MPL spectra indicates that they arise of a redistribution of the photoexcited holes within the energy states of the top valence band. This is caused by absorbing low-energy acoustic phonons that are emitted by the mw-heated 2DEG. We propose that these nonequilibrium phonons also affect the 2DEG mobility leading to the MIRO's. For B > 0.5 T and intense mw-irradiation, new optically detected resonances (ODRs) are observed at magnetic fields that depend on the 2DEG density and approximately correspond to integer electron filling factors. We argue that these resonances result from a slight 2DEG density increase under mw irradiation with a concurent, low-energy PL spectral shift due to a small bandgap narrowing.

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Lee, Sang Woon. "Two-Dimensional Electron Gas at SrTiO3-Based Oxide Heterostructures via Atomic Layer Deposition." Journal of Nanomaterials 2016 (2016): 1–9. http://dx.doi.org/10.1155/2016/1671390.

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Two-dimensional electron gas (2DEG) at an oxide interface has been attracting considerable attention for physics research and nanoelectronic applications. Early studies reported the formation of 2DEG at semiconductor interfaces (e.g., AlGaAs/GaAs heterostructures) with interesting electrical properties such as high electron mobility. Besides 2DEG formation at semiconductor junctions, 2DEG was realized at the interface of an oxide heterostructure such as the LaAlO3/SrTiO3(LAO/STO) heterojunction. The origin of 2DEG was attributed to the well-known “polar catastrophe” mechanism in oxide heterostructures, which consist of an epitaxial LAO layer on a single crystalline STO substrate among proposed mechanisms. Recently, it was reported that the creation of 2DEG was achieved using the atomic layer deposition (ALD) technique, which opens new functionality of ALD in emerging nanoelectronics. This review is focused on the origin of 2DEG at oxide heterostructures using the ALD process. In particular, it addresses the origin of 2DEG at oxide interfaces based on an alternative mechanism (i.e., oxygen vacancies).

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Xu, W. "Dynamical Properties of a Terahertz Driven Two-dimensional Electron Gas." Australian Journal of Physics 53, no. 1 (2000): 87. http://dx.doi.org/10.1071/ph99041.

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In this paper, I present a detailed theoretical study on how a nanostructure, such as a semiconductor-based two-dimensional electron gas (2DEG), interacts with a linearly polarised intense laser field. A tractable method in dealing with the time-dependent many-body problem has been developed, from which the electron Green's function, the electron density–density correlation function and the inverse dielectric function matrix for a 2DEG driven by intense laser fields have been obtained. Using these results, the influence of terahertz laser radiation on dynamical properties such as plasmon and optical spectra in a 2DEG is investigated. The results obtained from this study can be used for the case where the intense terahertz radiation is provided by recently developed free-electron laser sources.

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Feng, Qian, Peng Shi, Jie Zhao, Kai Du, Yu Kun Li, Qing Feng, and Yue Hao. "Transport Properties of Two-Dimensional Electron Gas in Cubic AlGaN/GaN Heterostructures." Advanced Materials Research 873 (December 2013): 777–82. http://dx.doi.org/10.4028/www.scientific.net/amr.873.777.

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We presented a theoretical study of the dependence of 2DEG mobility on temperature, barrier thickness, Al content, donor concentration to reveal the internal physics of 2DEG mobility in cubic AlGaN/GaNheterostructures. The 2DEG mobility is modeled as a combined effect of the scattering mechanisms including acoustic phonons, ionized impurity, dislocation, alloy disorder and interface roughness scattering.The variation of mobility results mainly from the change of 2DEG density and temperature. It reveals the dominant scattering mechanismsare dislocation and alloy disorder scattering atlow temperature.Acoustic phonons scattering becomes the major limit at 300k. Impurity scattering plays the key role when donor density rises. We find a maximum mobility with a structure of 25% Al content and 4-5nm barrier thickness.

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VYURKOV, VLADIMIR, ANDREY VETROV, and VICTOR RYZHII. "PSEUDO-GAP AND SPIN POLARIZATION IN A TWO-DIMENSIONAL ELECTRON GAS." International Journal of Nanoscience 02, no. 06 (December 2003): 619–24. http://dx.doi.org/10.1142/s0219581x03001747.

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Tunneling (one-particle excitation) density of states in the vicinity of Fermi level of a two-dimensional electron gas (2DEG) subjected to an external parallel and zero magnetic field is calculated. It reveals a pseudo-gap recently observed in the experiments. The gap originates in spin polarization of 2DEG. Nonmonotonic dependence of energy on a Landau level filling factor (density) for perpendicular magnetic field was also obtained. It implies the tunneling current peculiarities at filling factors of about 1/2 and 1. The Ising-like model of the exchange interaction in 2DEG was exploited instead of the conventional one. It was crucial to achieve even a qualitative agreement with experimental data.

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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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Zhou, Zhang-Wei, Jiu-Xun Sun, and Muhammad Ammar Khan. "Accurate ground-state variational wavefunction for the two-dimensional electron gas." International Journal of Modern Physics B 28, no. 21 (June 24, 2014): 1450148. http://dx.doi.org/10.1142/s0217979214501483.

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A variational wavefunction with two parameters is proposed for the two-dimensional electron gas (2DEG). The new wavefunction does not contain noninteger power of coordinate, and all integrals involving wavefunction can be analytically evaluated. This overcomes the shortcoming of the one proposed by Grinberg [ Phys. Rev. B 32, 4028 (1985)] which contains noninteger power of coordinate. The parameters have been determined by minimizing the average energy of an electron. The numerical results of energy and average separation of carriers for the ground state are in excellent agreement with the exact self-consistent (sc) results with average errors 0.21% and 0.57%. The accuracy is several times better than the wavefunction proposed of Grinberg with average errors 1.07% and 1.41%. The results also show that the triangular approximation for electric potential is correct as the density of 2DEG is low, but it deviates from the real situation as the density of 2DEG is high.

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Fossum, E. R., J. I. Song, and D. V. Rossi. "Two-dimensional electron gas charged-coupled devices (2DEG-CCD's)." IEEE Transactions on Electron Devices 38, no. 5 (May 1991): 1182–92. http://dx.doi.org/10.1109/16.78396.

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Usagawa, Toshiyuki, and Nobuko Mishima Araki. "Device analysis of two-dimensional electron gas (2DEG)FET." Electronics and Communications in Japan (Part II: Electronics) 71, no. 4 (1988): 59–71. http://dx.doi.org/10.1002/ecjb.4420710408.

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WANG, Y., A. P. LIU, J. BAO, X. G. XU, and Y. JIANG. "SPIN INJECTION INTO TWO-DIMENSIONAL ELECTRON GAS THROUGH A SPIN-FILTERING INJECTOR." Modern Physics Letters B 22, no. 16 (June 30, 2008): 1535–45. http://dx.doi.org/10.1142/s0217984908016273.

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In this paper, large spin polarization and magnetoconductance in a ferromagnet (FM)/ferromagnetic insulator (FI)/two-dimensional electron gas (2DEG)/non-magnetic insulator (I)/FM hybrid structure are theoretically predicted by introducing a spin-filtering injector. In the framework of coherent tunneling model, the electron transmission probability, spin polarization and magnetoconductance in the hybrid structure all oscillate with the electron density within the 2DEG channel. A complete single-mode spin injection would be realized by designing a well-defined geometry to adjust the competition between the spin-dependent tunneling of the conductive electrons and spin-filtering effect of the FI barrier.

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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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Rathore, Saad Ullah, Sima Dimitrijev, Hamid Amini Moghadam, and Faisal Mohd-Yasin. "Equations for the Electron Density of the Two-Dimensional Electron Gas in Realistic AlGaN/GaN Heterostructures." Nanomanufacturing 1, no. 3 (December 2, 2021): 171–75. http://dx.doi.org/10.3390/nanomanufacturing1030012.

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This paper presents equations for the electron density of the two-dimensional electron gas (2DEG) in AlGaN/GaN heterostructures in three realistic scenarios: (1) AlGaN/GaN heterostructure with surface exposed to ambient with mobile ions, (2) metal gate deposited on the AlGaN surface, and (3) a thick dielectric passivation layer on the AlGaN surface. To derive the equations, we analyzed these scenarios by applying Gauss’s law. In contrast to the idealistic models, our analysis shows that the 2DEG charge density is proportional to the difference between spontaneous polarization of AlGaN and GaN, whereas surprisingly, it is independent of the piezoelectric polarization.

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Lv, Meng, Guo Lin Yu, Yong Gang Xu, Tie Lin, Ning Dai, and Jun Hao Chu. "Magnetotransport Investigations of Two-Dimensional Electron Gas for AlGaN/GaN Heterostructure." Advanced Materials Research 1058 (November 2014): 132–35. http://dx.doi.org/10.4028/www.scientific.net/amr.1058.132.

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Magnetotransport properties are investigated in two-dimensional electron gas (2DEG) of AlGaN/GaN heterostructure, including the Drude conductance, the Shubnikov-de Haas (SdH) oscillations and the change with temperature, the electron-electron interaction (EEI) and the change with temperature, the weak antilocalization (WAL) and the change with temperature etc.

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Yu, Chen-hui, Qing-zhou Luo, Xiang-dong Luo, and Pei-sheng Liu. "Donor-Like Surface Traps on Two-Dimensional Electron Gas and Current Collapse of AlGaN/GaN HEMTs." Scientific World Journal 2013 (2013): 1–6. http://dx.doi.org/10.1155/2013/931980.

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The effect of donor-like surface traps on two-dimensional electron gas (2DEG) and drain current collapse of AlGaN/GaN high electron mobility transistors (HEMTs) has been investigated in detail. The depletion of 2DEG by the donor-like surface states is shown. The drain current collapse is found to be more sensitive to the addition of positive surface charges. Surface trap states with higher energy levels result in weaker current collapse and faster collapse process. By adopting an optimized backside doping scheme, the electron density of 2DEG has been improved greatly and the current collapse has been greatly eliminated. These results give reference to the improvement in device performance of AlGaN/GaN HEMTs.

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49

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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50

Sharbati, Samaneh, Iman Gharibshahian, Thomas Ebel, Ali A. Orouji, and Wulf-Toke Franke. "Analytical Model for Two-Dimensional Electron Gas Charge Density in Recessed-Gate GaN High-Electron-Mobility Transistors." Journal of Electronic Materials 50, no. 7 (April 20, 2021): 3923–29. http://dx.doi.org/10.1007/s11664-021-08842-7.

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AbstractA physics-based analytical model for GaN high-electron-mobility transistors (HEMTs) with non-recessed- and recessed-gate structure is presented. Based on this model, the two-dimensional electron gas density (2DEG) and thereby the on-state resistance and breakdown voltage can be controlled by varying the barrier layer thickness and Al mole fraction in non-recessed depletion-mode GaN HEMTs. The analytical model indicates that the 2DEG charge density in the channel increases from 2.4 × 1012 cm−2 to 1.8 × 1013 cm−2 when increasing the Al mole fraction from x = 0.1 to 0.4 for an experimental non-recessed-gate GaN HEMT. In the recessed-gate GaN HEMT, in addition to these parameters, the recess height can also control the 2DEG to achieve high-performance power electronic devices. The model also calculates the critical recess height for which a normally-ON GaN switch becomes normally-OFF. This model shows good agreement with reported experimental results and promises to become a useful tool for advanced design of GaN HEMTS.

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Journal articles on the topic 'Two Dimensional Electron Gas System (2DEG)'

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