Electron Gas Research Articles

Spin-dependent conductance and magnetoresistance ratio in two magnetic-barrier structures

An improved transfer matrix method is developed with modular matrices for rectangular electric and magnetic vector potentials, as well as the δ-function like potentials. As an example, the spin-dependent conductance in two-dimensional electron gas under modulation of two magnetic barriers are recalculated and compared with those illustrated in (Wang et al. Chin. Phys. B 19, 037301(2010)). The previous results are found inaccurate, their transfer matrix was derived for slowly varying magnetic vector potential, which is inappropriate for δ-function like Zeeman interaction potentials. Furthermore, the last transfer matrix of eq. (4) is also found incorrect, and the Zeeman interaction is wrongly expressed and mistakenly enhanced about (1/0.067 ≈ 15) times. Our improved method here is general and is demonstrated very fast forevaluating various spin-dependent transport properties in complex hybrid magnetic–electric structures.

Pseudo-proper two-dimensional electron gas formation

Abstract In spite of the interest in the two-dimensional electron gases (2DEGs) experimentally found at surfaces and interfaces, important uncertainties remain about the observed insulator–metal transitions (IMTs). Here we show how an explicit pseudo-proper coupling of carrier sources with a relevant soft mode significantly affects the transition. The analysis presented here for 2DEGs at polar interfaces is based on group theory, Landau–Ginzburg theory, and illustrated with first-principles calculations for the prototypical case of the LaAlO 3 / SrTiO 3 interface, for which such a structural transition has recently been observed. This direct coupling implies that the appearance of the soft mode is always accompanied by carriers. For sufficiently strong coupling an avalanche-like first-order IMT is predicted.

Heterojunction-engineered carrier transport in elevated-metal metal-oxide thin-film transistors

This study investigates the carrier transport of heterojunction channel in oxide semiconductor thin-film transistor (TFT) using the elevated-metal metal-oxide (EMMO) architecture and indium−zinc oxide (InZnO). The heterojunction band diagram of InZnO bilayer was modified by the cation composition to form the two-dimensional electron gas (2DEG) at the interface quantum well, as verified using a metal−insulator−semiconductor (MIS) device. Although the 2DEG indeed contributes to a higher mobility than the monolayer channel, the competition and cooperation between the gate field and the built-in field strongly affect such mobility-boosting effect, originating from the carrier inelastic collision at the heterojunction interface and the gate field-induced suppression of quantum well. Benefited from the proper energy-band engineering, a high mobility of 84.3 cm2·V−1·s−1, a decent threshold voltage (V th) of −6.5 V, and a steep subthreshold swing (SS) of 0.29 V/dec were obtained in InZnO-based heterojunction TFT.

High conductivity coherently strained quantum well XHEMT heterostructures on AlN substrates with delta doping

Polarization-induced two-dimensional electron gases (2DEGs) in AlN/GaN/AlN quantum well high-electron-mobility transistors on ultrawide bandgap AlN substrates offer a promising route to advance microwave and power electronics with nitride semiconductors. The electron mobility in thin GaN quantum wells embedded in AlN is limited by high internal electric field and the presence of undesired polarization-induced two-dimensional hole gases (2DHGs). To enhance the electron mobility in such heterostructures on AlN, previous efforts have resorted to thick, relaxed GaN channels with dislocations. In this work, we introduce n-type compensation δ-doping in a coherently strained single-crystal (Xtal) AlN/GaN/AlN heterostructure to counter the 2DHG formation at the GaN/AlN interface, and simultaneously lower the internal electric field in the well. This approach yields a δ-doped XHEMT structure with a high 2DEG density of ∼3.2×1013 cm−2 and a room temperature (RT) mobility of ∼855 cm2/Vs, resulting in the lowest RT sheet resistance 226.7 Ω/□ reported to date in coherently strained AlN/GaN/AlN HEMT heterostructures on the AlN platform.

Gate tunable edge magnetoplasmon resonators

AbstractQuantum Hall systems are platforms of choice to study topological properties of condensed matter systems and anyonic exchange statistics. In this work we have developed a tunable radiofrequency edge magnetoplasmonic resonator controlled by both the magnetic field and a set of electrostatic gates, meant to serve as a versatile platform for future interferometric devices designed to evidence non-abelian anyons. In our device, gates allow us to change both the size of the resonant cavity and the electronic density of the two-dimensional electron gas. We show that we can continuously control the frequency response of our resonator, making it possible to develop an edge magnetoplasmon interferometer. As we reach smaller sizes of our resonator, finite size effects caused by the measurement probes manifest. In the future, such device will be a valuable tool to investigate the properties of non-abelian anyons in the fractional quantum Hall regime.

A Novel Isolation Approach for GaN-Based Power Integrated Devices.

This paper introduces a novel technology for the monolithic integration of GaN-based vertical and lateral devices. This approach is groundbreaking as it facilitates the drive of high-power GaN vertical switching devices through lateral GaN HEMTs with minimal losses and enhanced stability. A significant challenge in this technology is ensuring electrical isolation between the two types of devices. We propose a new isolation method designed to prevent any degradation of the lateral transistor's performance. Specifically, high voltage applied to the drain of the vertical GaN power FinFET can adversely affect the lateral GaN HEMT's performance, leading to a shift in the threshold voltage and potentially compromising device stability and driver performance. To address this issue, we introduce a highly doped n+ GaN layer positioned between the epitaxial layers of the two devices. This approach is validated using the TCAD-Sentaurus simulator, demonstrating that the n+ GaN layer effectively blocks the vertical electric field and prevents any depletion or enhancement of the 2D electron gas (2DEG) in the lateral GaN HEMT. To our knowledge, this represents the first publication of such an innovative isolation strategy between vertical and lateral GaN devices.

Enhanced non-equilibrium Peltier cooling through electron gas expansion: A Monte Carlo simulation study

We demonstrate enhanced Peltier cooling at the nanoscale using geometrical constriction. This nozzle structure leads to electron expansion under an applied bias, which in turn results in additional cooling. This extra cooling enhances the overall Peltier effect when the electrons are out of equilibrium with the lattice. An ensemble Monte Carlo simulation is used to demonstrate the non-equilibrium expansion of an electron gas using nanoscale trapezoidal geometric confinement. The proposed device operates under steady-state conditions, providing enhanced cooling compared to a one-dimensional flat geometry. We observe a five-fold increase in both the maximum cooling temperature and cooling power density, reaching more than 5 kW/cm2, when comparing the trapezoidal geometry to the regular flat geometry.

Measurement of fast neutron induced (n,γ) reaction cross-section of 68Zn, 96Zr, 121Sb and 123Sb in the energy range of 1 to 2 MeV

The (n,γ) reaction cross-section for the elements 68Zn, 96Zr, 121Sb and 123Sb, present in the reactor structural/shielding materials, was measured by neutron activation technique in the neutron energy region of 1–2 MeV as very limited data is available in this energy range. Further, the neutron spectrum peaks in this energy region for the fast breeder reactors and proposed accelerator driven sub-critical systems. The natural strontium (natSr) element was used as a neutron flux monitor by considering effective combined reaction cross-section for 86Sr(n,γ)87Srm and 87Sr(n,n′)87Srm reactions. The pellets of mixture of sample and monitor were irradiated by a quasi-mono energetic fast neutron beam, generated by 7Li(p,n)7Be reaction at FOTIA, Bhabha Atomic Research Centre, Mumbai, India. The activity of activation products was measured by off-line gamma-ray spectrometry using High Purity Germanium Detector (HPGe). The present data with improved uncertainty and covariance analysis enhance the cross-section data base for better constraining the evaluated data and theoretical models. The theoretical (n,γ) reaction cross-sections were calculated using TALYS 1.96, which could reasonably explain the present data with the Fermi gas level density prescription.

Effects of Band Nonparabolicity on the Resonance Peaks of the Single-Particle Entropy of a Two-Dimensional Electron Gas

Effects of Band Nonparabolicity on the Resonance Peaks of the Single-Particle Entropy of a Two-Dimensional Electron Gas

Low Disorder and High Mobility 2DEG in Si/SiGe Fabricated in 200 mm BiCMOS Pilot line

Spin qubits based on quantum dots built on Si/SiGe heterostructures are a leading contender for achieving large-scale quantum computation. The quality of quantum dots fabricated on these heterostructures is directly connected to the quality of the 2D electron gas (2DEG) confined in the strained Silicon quantum well. The properties of such 2DEG can be readily assessed using Hall bar-shaped field-effect transistors (HB-FETs) and magneto-transport measurements, enabling a faster feedback loop for heterostructure optimization process. In this work, we present our recent progress in enabling silicon-based quantum computation by demonstrating fundamental components for 2DEG characterization, all developed in IHP's 200 mm BiCMOS pilot line. We demonstrate fully functional HB-FETs on Si/SiGe heterostructures grown on 200 mm silicon wafers, showcasing state-of-the-art 2DEG with maximum carrier mobility exceeding 300,000 cm²/Vs and a percolation threshold of 6.3×1010 cm⁻². These results will help advance spin qubit research based on Si/SiGe heterostructures.

Investigation of the production routes of 81,82m,83,84 Rb isotopes through proton-induced nuclear reactions on 82,83,84,86 Kr

Investigations using nuclear reaction models are significant and have considerable consequences in terms of understanding nuclear reaction processes and their nature. The nuclear data on radionuclides created by the cyclotron find application in nuclear diagnostics and therapeutic treatments. The excitation function of proton-induced nuclear reactions on 82,83,84,86 Kr for the generation of medically beneficial short-lived radioisotopes 81,82m,83,84 Rb from threshold energy to 50 MeV has been investigated using Koning–Delaroche optical model potential with nuclear level density (NLD) from both the phenomenological and microscopic nuclear models incorporated in TALYS1.96 code. The phenomenological constant temperature + Fermi gas model, back-shifted Fermi gas model, generalised superfluid model, and microscopic NLD from the Skyrme–Hartree–Fock–Bogoliubov, Gogny–Hartree–Fock–Bogoliubov, and temperature-dependent Gogny–Hartree–Fock–Bogoliubov NLD tables have been used to calculate the excitation function. The calculated excitation functions are compared with the experimental data from EXFOR and the TALYS evaluated nuclear data library (TENDL2023). An analysis is carried out by estimating the mean deviation D-value between the theoretical and experimental cross-sections, and the NLD model corresponding to the best result is used for the estimation of activity and production yield for each reaction channel.

Ce-doped ZnO nanonails synthesized by a simple thermal evaporation method for photocatalytic degradation

One-dimensional (1D) nanomaterials have garnered significant scientific and technological attention due to their potential applications in electronics devices, gas sensing, energy conversion, and photocatalysis. However, the development of a simple and low-cost technique for 1D nanostructure synthesis remains a challenge. The doping of ZnO nanostructures has proven to be an effective way to improve their internal properties. In this work, one-dimensional ZnO and Ce-doped ZnO nanorods and nanonails were synthesized by a simple thermal evaporation method using different weight ratios of ZnS and CeO2 precursor powders in a catalyst-free process. The effects of cerium doping concentration on the structural, morphological, and optical properties of the as-prepared samples were investigated. XRD analysis confirmed that the crystal structure was converted from the cubic ZnS phase to the hexagonal ZnO phase with increasing annealing temperatures. The UV–Vis spectra showed that the optical absorption edge of Ce-doped ZnO samples was slightly red-shifted. Additionally, the band gap energy decreases with increasing cerium concentration. SEM images showed that the morphology of the structures obtained changed from nanorods to nanonails as the Ce content increased. The incorporation of Ce ions into the ZnO matrix has been successfully confirmed by HRTEM, Raman, and EDX analysis. Photocatalytic activity studies showed that Ce-doped ZnO samples exhibited significantly enhanced photocatalytic performance compared to pure ZnO for the degradation of rhodamine B under UV radiation. These results may suggest the use of heterogeneous photocatalysis as an efficient, cheap, and environment-friendly alternative for the removal of pollutants from water and the use of Ce-doped ZnO as a promising candidate.

Numerical analysis on the performance enhancement in AlGaN/GaN vertical CAVET with InGaN/AlN/InGaN hybrid current blocking layer

Abstract In this paper, we propose an enhanced superjunction AlGaN/GaN vertical current aperture vertical electron transistor (CAVET) that integrates a novel hybrid InGaN/AlN/InGaN current blocking layer (CBL) situated above the P-column, directly beneath the channel. The incorporation of InGaN substantially elevates the device’s saturation output current by introducing a subchannel beneath the AlGaN/GaN heterojunction conducting channel. Nonetheless, the introduction of AlN engenders a two-dimensional hole gas of opposite polarization direction via the GaN/AlN heterojunction, which aids in depleting the two-dimensional electron gas within the channel, thereby mitigating the issue of negative threshold voltage (V th) bias occasioned by the subchannel introduced by InGaN. The outcomes demonstrate that the maximum saturation output current (I d) for the proposed architecture is 361.5 mA mm−1, with a V th of 1.63 V, marking increases of 98.6% and 0.08% over the traditional superjunction CAVET, respectively. Simultaneously, the breakdown voltage (V br) of the designed device is recorded at 12 064 V, and the specific on-resistance (R on,sp) is 6.45 Ω·mm, showcasing a enhancement figure of merit of 32.9% in comparison to the traditional superjunction CAVET.

Enhanced capability of model fitting to nuclear level density and heat capacity: testing on 93−98Mo nuclei

We propose an improved fitting approach that improves reliability in studying the nuclear level density (NLD) and thermodynamic quantities. The proposed method, which relies on the fact that experimental fluctuations or outliers, if they exist, should not be involved in the fitting process, is validated with a set of data artificially generated with anomalous data points being intentionally inserted. In order to showcase the advantages of the proposed technique, we have applied it to re-investigate the back-shifted Fermi gas (BSFG) level density parameters and thermodynamic quantities, particularly the heat capacities, of 93−98Mo isotopes. We have found that the range of values for the level density parameter of 93Mo (approximately from 8.5 to 9.0 MeV−1) is notably smaller than that obtained for the other isotopes of Mo (approximately from 10.5 to 11.5 MeV−1). This observation is different from previous predictions, in which the values of level density parameter of all Mo isotopes are in the same range. This is because among the Mo isotopes under examination, 93Mo (N = 51 neutrons) has the smallest number of valence neutrons, namely only a single neutron away from the closed N = 50 shell. In addition, thanks to the proposed method, we have discussed the effects of data fluctuations on the BSFG NLDs and thermodynamic quantities of 93−98Mo isotopes, from which our recommendation for future works is announced. On top of that, we should notice that the proposed approach can be further applied to any work involving the fitting of a phenomenological model to empirical data.

Fully polarized Fermi systems at finite temperature.

We propose a simple model of an interacting, fully spin-polarized Fermi gas in dimensions d=2 and d=3, and derive the approximate expression for the energy spectrum and the corresponding formula for the Helmholtz free energy. We analyze the thermodynamics of the system and find the lines of first-order phase transitions between the low- and high-density phases terminating at critical points. The properties of the corresponding phase diagrams are qualitatively different for d=2 and 3, and sensitively depend on the interparticle attraction, which marks a departure from the standard van der Waals theory. The differences originate from the Pauli exclusion principle and are embedded in the fermionic nature of the system under study.

Unveiling the tunable electronic, optoelectronic, and strain-sensitive gas sensing properties of Janus ZrBrCl: Insights from DFT study

Janus monolayers materials exhibit extraordinary physical and chemical properties because of crystal field changes caused by their asymmetric structures. Here, we investigate the electronic, switching, optoelectronic, and strain-sensitive gas-sensing properties of a Janus ZrBrCl monolayer via density-functional theory and the nonequilibrium Green’s function methods. The electronic properties can be tuned by applying biaxial strain and electric fields. In particular, the band gap can be changed from indirect to direct via applied a + 8 % biaxial tensile strain. It can be transformed from a semiconductor to a metal with an applied −14 % biaxial compressive strain, with a 1011 switching ratio. In addition, a biaxial strain and an electric field can modulate visible light absorption and photocurrents. Under a −12 % biaxial compressive strain, the absorption coefficient increased to 5.26 × 105 cm−1 from the intrinsic 4.08 × 105 cm−1. Across biaxial strains from −4% to + 4 %, the photocurrent density peak displayed red and blue shifts, respectively, with increasing tensile and compressive strains. NH3, NO2, and NO physically adsorb on the Br side of the ZrBrCl monolayer. Maximum gas sensitivity values of a ZrBrCl sensor are 52 % in the zigzag direction and 21 % in the armchair direction. After application of the −14 % biaxial strain, the maximum values respectively increased to 76 % and 179 %. The biaxial compressive strain-sensitive gas-sensing properties are driven by changes in the electrostatic potential difference between the Br and Cl surfaces. These findings indicate promising candidate materials for high-performance switching and optoelectronic devices, and also provide a strategy for improved gas sensors.

Improving spin manipulation in HgTe/CdTe quantum wells via electrical means

We present a theoretical investigation of electron transport properties through a two-dimensional electron gas (2DEG) HgTe/CdTe quantum wells (QWs) heterostructure that incorporate two Rashba-modulated regions. Our study demonstrates that the transmission can be effectively tuned by varying the Rashba spin-orbit coupling (RSOC) strength, Fermi energy, and electrical voltage. Efficient spin-conserving and spin-flip transmission can be achieved by adjusting the RSOC modulation strength. Furthermore, fully spin-polarized spin or current transmission with PZ=±1, as well as complete spin-flip conversion with a rate of Tsf=1 are attained by fine-tuning the amplitudes of the two Rashba modulations using gate voltage or adjusting the RSOC strength. This electrical mechanism provides a convenient approach to electrically manipulate both spin and charge currents, which holds promise for low-power device applications.

Discovering the incorporation limits for wurtzite AlPyN1−y grown on GaN by metalorganic vapor phase epitaxy

We report on the growth of AlPN on GaN/sapphire templates by metalorganic vapor phase epitaxy using tertiarybutylphosphine (tBP) and NH3 as group-V precursors. P is easy to incorporate into the group-III lattice site, forming PAl anti-site defects and shrinking lattice constants that are even beyond AlN since Al is larger than P. We found that higher temperatures favor P incorporation on the N-sublattice, forming AlPyN1−y, while growth temperatures below 1000 °C result in dominant P incorporation on the Al-sublattice, forming PAl anisites. Similarly, larger NH3 flows stabilize GaN, leading to flat interfaces, but favor the formation of PAl. Furthermore, the P incorporation into AlPyN1−y is non-linear. At very low tBP flows, it initially increases to reach a maximum. Further increasing the tBP flow increases mostly the incorporation of P on the Al-sublattice, and the c-lattice constant decreases again. This leaves a small window of low V/III ratios below 5 and low P/N ratios of 1% or smaller, leading up to ∼4% P incorporation at typical growth temperatures of GaN. However, at such low V/III ratios, GaN is not stable even with N2 carrier gas and requires optimized switching sequences to minimize its decomposition and preserve flat interfaces. Eventually, a 10 nm coherent layer of AlP0.01N0.99 could be reproducibly grown on top of GaN channels with a smooth surface, an abrupt AlPN/GaN interface, and a two-dimensional electron gas with an electron mobility of ∼675 cm2/V s and a sheet carrier density of 1.5 × 1013 cm−2 at room temperature.

Contact potential difference in the absence of current through the sample in the quantum hall effect regime in InGaAs/InAlAs heterostructure

The paper presents experimental results of the appearance of voltage at potential contacts in the absence of an external current through the sample in the plateau region of the quantum Hall effect in a heterostructure with an InGaAs/InAlAs quantum well. The occurrence of voltage is associated with the non-equivalence of edge current in potential contact areas in a magnetic field in a system with a two-dimensional electron gas.

Integrating NiSe2-MoSe2 heterojunctions with N-doped porous carbon substrate architecture for an enhanced electrocatalytic water splitting device

The development of sustainable energy technologies relies on the exploitation of efficient and durable electrocatalysts for water splitting at high current densities. Our work presents a novel bifunctional catalyst, denoted as NM@NC/CC, which combines the benefits of NiSe2-MoSe2 heterojunctions with nitrogen-enriched porous carbon derived from metal-organic frameworks (MOFs). The integration of these components is designed to harness their combined advantages, which include enhanced electron transfer, improved mass and gas evolution dynamics, and an increased number of catalytically active sites. These features collectively optimize the energetics for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). As a result, the catalyst facilitates rapid kinetics for the overall water-splitting process. The NM@NC/CC demonstrates low overpotentials, requiring only 91 mV for the HER and 280 mV for the OER to reach a current density of 10 mA cm−2. Even at higher current densities of 100 mA cm−2 for HER and 50 mA cm−2 for OER, the overpotentials are only 159 mV and 350 mV, respectively. Additionally, a two-electrode setup using this catalyst achieves a current density of 10 mA cm−2 with a minimal cell voltage of 1.56 V. The insights gained from this study will contribute to the advancement of electrocatalysts for energy conversion technologies.