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MoS2 can be used for piezoresistive sensors because of its excellent mechanical and electrical properties. Herein, MoS2 nanoparticles with sulfur vacancies synergistically coupled with grain clusters to boost piezoresistive properties are fabricated. Moreover, we have demonstrated that they can be regulated efficiently for gauge factor (GF) from 2.97 to 9.99. In particular, the MoS2 nanoparticles with sulfur vacancies of 31.8% and grain cluster of 29.6 nm at the annealing temperature of 500 °C are compatible with synergistic optimization. The abundant sulfur vacancies provide many free electrons as carriers, benefiting the electron transport capability, and the conductive channels formed by the larger grain clusters endow structural stability and significant piezoresistive properties of the nanoparticles. This work demonstrates the promise of MoS2 nanoparticles as novel piezoresistive advanced materials. [ABSTRACT FROM AUTHOR]

Granular metals (GMs), consisting of metal nanoparticles separated by an insulating matrix, frequently serve as a platform for fundamental electron transport studies. However, few technologically mature devices incorporating GMs have been realized, in large part because intrinsic defects (e.g., electron trapping sites and metal/insulator interfacial defects) frequently impede electron transport, particularly in GMs that do not contain noble metals. Here, we demonstrate that such defects can be minimized in molybdenum–silicon nitride (Mo–SiNx) GMs via optimization of the sputter deposition atmosphere. For Mo–SiNx GMs deposited in a mixed Ar/N2 environment, x-ray photoemission spectroscopy shows a 40%–60% reduction of interfacial Mo-silicide defects compared to Mo–SiNx GMs sputtered in a pure Ar environment. Electron transport measurements confirm the reduced defect density; the dc conductivity improved (decreased) by 104–105 and the activation energy for variable-range hopping increased 10×. Since GMs are disordered materials, the GM nanostructure should, theoretically, support a universal power law (UPL) response; in practice, that response is generally overwhelmed by resistive (defective) transport. Here, the defect-minimized Mo–SiNx GMs display a superlinear UPL response, which we quantify as the ratio of the conductivity at 1 MHz to that at dc, Δ σ ω. Remarkably, these GMs display a Δ σ ω up to 107, a three-orders-of-magnitude improved response than previously reported for GMs. By enabling high-performance electric transport with a non-noble metal GM, this work represents an important step toward both new fundamental UPL research and scalable, mature GM device applications. [ABSTRACT FROM AUTHOR]

2D Janus Rashba semiconductors, which break both the mirror symmetry in the crystal structure and the spin degeneracy in the energy band, provide a promising platform to optimize thermoelectric performance. Herein, we use first-principles and Boltzmann transport theory to investigate the electron and phonon transport properties for Janus semiconductors of monolayer Si2AsSb and Si2SbBi. The strong Rashba spin-splitting is found in both Janus monolayers especially for Si2SbBi, which decreases the bandgaps and makes the valence bands more dispersive, resulting in decreased p-type Seebeck coefficient and increased p-type electrical conductivity. The lattice thermal conductivities of both monolayers are not low due to the weak phonon anharmonicity, strong chemical bonding, and long phonon relaxation time. The low lattice thermal conductivity of Si2SbBi than Si2AsSb mainly originates from the low phonon group velocity. Both monolayers exhibit better thermoelectric performance in n-type than in p-type. The competition among Seebeck coefficient, electrical conductivity, and electronic thermal conductivity makes the difference of optimal thermoelectric figure of merits in n-type without and with Rashba spin–orbit coupling slight for Si2AsSb, but it is significant for Si2SbBi. Within Rashba spin–orbit coupling, the optimal figure of merits at 700 K reach 0.65 and 0.59 for Si2AsSb and Si2SbBi, respectively, which indicate the potential thermoelectric applications, and will stimulate the broad study on thermoelectric properties of 2D Janus Rashba semiconductors. [ABSTRACT FROM AUTHOR]

Noting that the conventional collision-dominated electron transport perspective is only relevant when the length scale over which the transit occurs is greater than the electron's mean free path, one can conceptually partition the electron transport "space" into collision-dominated and ballistic electron transport regimes. As the boundaries between these regimes are quite porous, in this analysis, we devise a means of quantitatively examining the transition between electron transport regimes as the length scale is reduced on a continuum basis. Our approach introduces a collision-dominated fractional scattering parameter, this parameter quantifying the fraction of the total scattering rate that arises purely from bulk scattering processes, contact scattering also contributing to the total scattering rate. We pursue this analysis for two conventional semiconductors of interest, silicon and gallium arsenide. A determination of the dependence of the results on both the length scale and the crystal temperature is pursued. Finally, for the specific case of room temperature, a comparison with the results of experiment is performed. [ABSTRACT FROM AUTHOR]

In this manuscript, carrier transport simulation methods are proposed for devices with the coexistence of quantum transport and diffusive transport by combining the nonequilibrium Green's function method with the drift-diffusion transport simulation method. Current continuity between quantum transport and drift-diffusion transport is ensured by setting quantum transport current as the connection boundary condition of drift-diffusion simulation or by introducing quantum transport-induced carrier generation rates to drift-diffusion simulation. A comprehensive study of our method and the method combining the Wentzel–Kramers–Brillouin (WKB) method with the drift-diffusion transport simulation method is performed for n-type tunnel oxide passivating contact solar cell to investigate their applicable conditions and balance the accuracy and computational cost. As the oxide barrier width, barrier height, and electron effective mass increase, or the doping concentration in the electron transport layer decreases to the extent that the blocking effect of the oxide barrier on light-generated electrons becomes significant, method I is more accurate since the transmission coefficient near the conduction band edge calculated by WKB is overestimated; otherwise, method II is more suitable due to its low computational cost without the loss of accuracy. In addition, the differences between current densities, carrier densities, and Shockley–Read–Hall recombination rates simulated under the two current continuity conditions for the solar cell with different carrier mobilities are also further explored and analyzed. [ABSTRACT FROM AUTHOR]

Current–voltage characteristics, space- and time-resolved optical emission spectroscopy, and 1D fluid modeling are used to examine the effect of dual-frequency sheath oscillations on the ion and electron transport in dielectric barrier discharges sustained by a combination of low frequency (LF, 50 kHz, 650 V) and radiofrequency (RF, 5.3 MHz, 195 V) voltages, exhibiting the α-to-γ mode transition. On one hand, when polarities of the LF and RF voltages are opposite, an electric field near the LF cathode (due to LF cathode sheath) drives the secondary electrons to the plasma bulk and an opposite electric field between the sheath edge and the LF anode attracts the electrons toward the LF cathode (to maintain quasi-neutrality in the plasma bulk). At the sheath edge, electrons become trapped and ions drift toward the cathode and the anode simultaneously according to their position in the gap. On the other hand, when the RF voltage has the same polarity as the LF voltage, the total applied voltage increases and this yields to enhanced production of electrons and ions in the sheath. To maintain quasi-neutrality in the bulk, the electric field along the gap exhibits the same polarity as the one in the sheath, allowing electrons created in the sheath to be evacuated toward the LF anode. The behavior of the LF cathode is, therefore, controlled by the LF sheath, and, thus, by the LF voltage amplitude, while the behavior in the bulk and at the anode alternates on the time scale of the RF voltage. [ABSTRACT FROM AUTHOR]

Efficient thermoelectric energy conversion at the nanoscale could power the Internet of Things and cool nanoelectronic circuits and improve the performance of quantum applications. Width-modulated nanowaveguides are suitable for these purposes because their thermoelectric efficiency can be geometrically tuned and integrated into the nanoelectronics industry processes. They are attracting increasing research interest stimulated by theoretical predictions for exceptional performance. To validate their potential, a better understanding of the effect of width modulation on thermoelectric efficiency is needed. So far, it is considered that (a) the thermoelectric efficiency increases monotonically with increasing width-mismatch due to decreasing phonon thermal conduction taking place without significantly affecting electron transport, (b) width-mismatch dominates the effect of width modulation in transport, and (c) phonons play the main role in increasing the thermoelectric efficiency. Here, we demonstrate counterevidence based on an investigation of the effect of width modulation on electrons so far overlooked. We reveal that (a) the thermoelectric efficiency varies non-monotonically with the modulation mismatch due to quantum effects on electron transport, (b) the modulation mismatch is quantified by the size-mismatch of the modulation rather than by the width-mismatch, and (c) it is electrons rather than phonons that play the main role in optimizing width modulation for maximum thermoelectric efficiency when quantum effects dominate. Our findings indicate that research should reorient from large width-mismatch toward optimal modulation-mismatch width-modulated nanostructures to enhance thermoelectric efficiency due to quantum effects. Our work provides new insight for designing nanowaveguides for efficient thermoelectric energy conversion at the nanoscale. [ABSTRACT FROM AUTHOR]

Electron emission and transport through and over potential barriers is an essential process requiring modeling and simulation to meet the design needs and characterization of an exceedingly broad range of technologically important devices and processes. The simulation and description of thermal, field, and photoemission, and the related concerns of space–charge affected electron flow, often make use of specialized formulations developed in the early days of quantum mechanics. Advancements in the utilization of electron sources and particularly the simulation of devices and applications using advanced particle-in-cell and trajectory methods for beam optics codes create a strong need for a pedagogical account of the emission models to ensure correct numerical evaluation of their equations. This Tutorial starts from simple phenomenological accounts and progressively builds to comprehensive models emphasizing straightforward and often rapid calculation. It recommends formulations to supplant the canonical Richardson–Laue–Dushman (thermal), Fowler–Nordheim (field), Fowler–DuBridge (photo), and Baroody (secondary) equations and provides a useful formulation of space–charge affected flow commonly described by the Child–Langmuir relation that takes into account cathode dependence on surface field. [ABSTRACT FROM AUTHOR]

We report on the study of electron transport and band offset across β -Ga 2 O 3 /4H-SiC N–n isotype heterojunction. N-type β -Ga 2 O 3 of thickness 2.7 μ m was grown using low-pressure chemical vapor deposition using germanium (Ge) as the dopant on an n-type 4H-SiC substrate. The grown epilayer having (− 201) orientation was verified through XRD. Temperature-dependent I–V and C–V measurements were performed (50–300 K) to investigate the transport properties across the heterojunction. First, lateral diodes were fabricated on β -Ga 2 O 3 , and from C–V, n-doping was estimated to be 2.3 × 10 17 cm − 3 in the epilayer while the Schottky barrier height was estimated to be 1.75 eV. In top-down I–V sweeps, the reverse current across the heterojunction exhibited marginal dependence on temperature, indicating a possible tunnelling-based transport mechanism, while the forward current exhibited an exponential dependence on both temperature and the applied bias. The band diagram indicated the formation of a two-dimensional electron gas (2DEG) at the hetero-interface, which was indirectly confirmed using C–V measurement and TCAD simulation at low temperatures. From the position of the Fermi level in SiC and band diagram, a conduction band offset of 0.4–0.5 eV was estimated between β -Ga 2 O 3 and 4H-SiC. [ABSTRACT FROM AUTHOR]

In recent years, organic–inorganic hybrid perovskite (PVK) devices have attracted widespread attention with their high absorption coefficient and low-cost fabrication process. Formamidinium lead iodide (FAPbI3) perovskite solar cells (PSCs) have been reported to obtain high power conversion efficiencies (PCEs) due to the narrow bandgap. Zinc oxide (ZnO) has better electrical conductivity and high transmittance than tin (IV) dioxide (SnO2). However, the deprotonation behavior of ZnO limits its use in formamidinium (FA) or methylammonium (MA) devices, so it is mostly used in all-inorganic PSCs. In this work, to avoid the deprotonation behavior of ZnO, we prepared FAPbI3 PSCs using ZnO/SnO2 as bilayer electron transporting layers (ETLs), which improved the conductivity of the ETLs and promoted electron extraction and transfer. In addition, the decrease in the oxygen vacancy (Ov) on the bilayer ETLs contributed to the suppression of the non-radiative recombination of the device, thus enabling the achievement of a higher fill factor. As a result, the modified ETLs increased the PCE of FAPbI3 PSCs from 20.24% to 21.42% and improved the stability of the devices. The PCE of unpackaged devices increased steadily to 21.91% when stored in an N2 atmosphere for 183 days. [ABSTRACT FROM AUTHOR]

Rutile-type wide and ultrawide band-gap oxide semiconductors are emerging materials for high-power electronics and deep ultraviolet optoelectronics applications. A rutile-type GeO2-SnO2 alloy (r-GexSn1–xO2) recently found is one of such materials. Herein, we report low-temperature electron transport properties of r-GexSn1−xO2 thin films with x = 0.28 and 0.41. Based on resistivity and magnetoresistance measurements, along with the theory of quantum interference, it is suggested that Efros–Shklovskii variable-range hopping, i.e., hopping over the states within the Coulomb gap, is dominant at lower temperatures (T ≤ 10 and 15 K) in both r-Ge0.41Sn0.59O2 and r-Ge0.28Sn0.72O2. The negative and positive magnetoresistances observed at low temperatures are attributable to the quantum interference and field-induced spin alignment, respectively. The magnetoresistance measurements at higher temperatures suggest that both Mott variable–range hopping and thermally activated band conduction occur at T < 100 K and that almost pure thermally activated band conduction takes place at T ≥ 150 K. [ABSTRACT FROM AUTHOR]

Rutile-type wide and ultrawide band-gap oxide semiconductors are emerging materials for high-power electronics and deep ultraviolet optoelectronics applications. A rutile-type GeO2-SnO2 alloy (r-GexSn1–xO2) recently found is one of such materials. Herein, we report low-temperature electron transport properties of r-GexSn1−xO2 thin films with x = 0.28 and 0.41. Based on resistivity and magnetoresistance measurements, along with the theory of quantum interference, it is suggested that Efros–Shklovskii variable-range hopping, i.e., hopping over the states within the Coulomb gap, is dominant at lower temperatures (T ≤ 10 and 15 K) in both r-Ge0.41Sn0.59O2 and r-Ge0.28Sn0.72O2. The negative and positive magnetoresistances observed at low temperatures are attributable to the quantum interference and field-induced spin alignment, respectively. The magnetoresistance measurements at higher temperatures suggest that both Mott variable–range hopping and thermally activated band conduction occur at T < 100 K and that almost pure thermally activated band conduction takes place at T ≥ 150 K. [ABSTRACT FROM AUTHOR]

The lattice mismatch, defect, and weak interlayer coupling severely constrain the practical application of van der Waals heterojunctions (vdWHs) in the field of optoelectronic devices. Here, we introduced the 2D ferroelectric (FE) material AgBiP2Se6 to construct defect-free, low lattice-mismatched AgBiP2Se6/MoSe2 heterojunctions with different polariton directions (I, II, III). The AgBiP2Se6 layer can provide an excellent FE electric field to enhance the interlayer coupling and stiffness. The larger interlay stiffness reduces the probability of electron–phonon scattering and then results in significant carrier mobility (∼0.5 × 104 cm2 V−1 s−1) for configurations I and II. Phase transition of FE to paraelectric AgBiP2Se6 in the AgBiP2Se6/MoSe2 heterojunctions can be achieved under specific biaxial strain, which can effectively regulate the electronic structure. Applying the strain and electric field can regulate the bandgap and band alignment of configurations I and II. The photoelectric conversion efficiency of configuration I can reach as high as 20.54% under 2% biaxial strain. Furthermore, configuration II holds a nearly free electron state near the Fermi level under an electric field, which can act as a favorable electron transport channel. A design to strengthen interlayer coupling in the FE-based AgBiP2Se6/MoSe2 heterojunction has been proposed, and it can provide a new way to break through the traditional bottleneck in the development of optoelectronic devices. [ABSTRACT FROM AUTHOR]

We demonstrate a high electron conductivity (>102 S/cm and up to 103 S/cm) of tungsten suboxide W18O52.4−52.9 (or equivalently WO2.91−2.94) nanotubes (2–3 nm in diameter, ∼μm long). The conductivity is measured in the temperature range of 120–300 K by a four-probe scanning tunneling microscope in ultrahigh vacuum. The nanotubes are synthesized by a low-temperature and low-cost solvothermal method. They self-assemble in bundles of hundreds of nanotubes forming nanowires (∼μm long, few tens nm wide). We observe a large anisotropy of the conductivity with a ratio (longitudinal conductivity/perpendicular conductivity) of ∼105. A large fraction of them (∼65%–95%) shows a metallic-like, thermal activation-less electron transport behavior. Few of them, with a lower conductivity from 10 to 102 S/cm, display a variable range hopping behavior. In this latter case, a hopping barrier energy of ∼0.24 eV is inferred in agreement with the calculated energy level of the oxygen vacancy below the conduction band. This result is in agreement with a relative average concentration of oxygen vacancies of ∼3%, for which a semiconductor-to-metal transition was theoretically predicted. These tungsten suboxide nanostructures are prone to a wide range of applications in nanoelectronics. [ABSTRACT FROM AUTHOR]

Within the framework of an electron transport regime classification scheme, we aim to explore the boundaries that occur between the ballistic, collision-dominated, space-charge injection, and non-space-charge injection electron transport regimes that are experienced by an electron within a semiconducting device, mapping out where these different electron transport regimes are. We do this by determining the electron's mean free path and the relevant screening length. In order to make this analysis concrete, we perform this analysis for four representative semiconductor material systems, including silicon, gallium arsenide, the 4H-phase of silicon carbide, and the wurtzite phase of gallium nitride. The entire analysis is performed using a two-dimensional approach, this being representative of the electron transport that is experienced by an electron in the vicinity of a two-dimensional electron gas. Finally, following an evaluation of the dependence of the ballistic mobility on the device length scale for all four materials, an evaluation of the effective mobility as a function of the channel-length scale is pursued, a Matthiessen-rule based approach being employed for the purposes of this analysis. [ABSTRACT FROM AUTHOR]

The electron transport characteristics of magnetic and non-magnetic ferroelectric tunnel junctions based on Hf 0.5 Zr 0.5 O 2 are investigated in this study. A modified linear approach to the Thomas–Fermi interfacial screening model is employed to simulate these properties. This method is developed by leveraging the quantum approximation of the quasiclassical spin-resolved point-like contact formalism. The oxygen vacancies, voltage-induced screening, and electrostriction effect are the key phenomena exploited to build the potential profile and hence to simulate the resistive switching characteristics of the ferroelectric tunnel junctions. To validate its precision, the model is extensively verified with experimental data. The obtained model is generalized to reproduce mono-domain and multi-domain ferroelectric switching, featuring its effectiveness for non-volatile storage devices and ferroelectric-field effect transistors. [ABSTRACT FROM AUTHOR]

A memristor is a two-terminal electrical component with the scope of future computing applications and analog electronics. In this report, bismuth sulfide decorated one-dimensional carbon nitride nanotube was synthesized and characterized with various analytical techniques. The electrical property of the synthesized material was measured using a two-terminal metal–insulator–metal type of device that exhibited the resistive switching characteristics with the ON to OFF ratio of 2 × 103. The electron transport mechanism of the device was followed by Schottky emission and Poole–Frenkel emission for a low conductance state and Ohmic conduction behavior at the high conductance state. A decrease in the trap depth was identified in the simulation study with increasing applied potential and that supported the proposed mechanism. Read endurance and retention behavior of the device are stable in nature, supported by the statistical analysis. Furthermore, a hybrid logic gate was designed using two identical memristors, one CMOS inverter, one resistor, one voltage divider, and a buffer gate. The designed logic gate exhibited stable nand and nor gate operation based on the control signal. [ABSTRACT FROM AUTHOR]

A theoretical treatment of the multiple scattering problem for electrons in heavily doped semiconductors is developed for the purpose of resolving a long-standing discrepancy between theory and experiment on electron transport in semiconductors and semimetals. The scattering strength term in the traditional Brooks–Herring formula for ionized impurity scattering is modified to take into account the effect of the spatial proximity of ionized donors leading to an additional scattering term proportional to the cube of ionized impurity concentration, whereas the Brooks–Herring theory varies strictly linearly with the ionized impurity concentration. Comparisons between theory and experiment for GaAs, GaN, ZnO, and α-Sn are presented, showing significant improvement overall. In some cases, improvements greater than an order of magnitude are achieved. The agreement between theory and experiment for heavily doped ZnO over the temperature range of 21–322 K is within about 1%, depending on temperature. [ABSTRACT FROM AUTHOR]

Reducing the gap between the electrodes to the nanoscale and utilizing quantum effects are an effective way to enhance the performance of a thermionic energy device. In this work, we establish the model of a photon-enhanced thermionic emission system with a nanoscale vacuum gap, where the electron transport due to electron tunneling and the near-field radiation resulting from photon tunneling are introduced. Analytical expressions for the thermionic emission current, electron tunneling current, and heat flux due to the near-field radiation are provided. By using the energy and particle balance equations, the electron concentration and the temperature of the cathode are determined. The impacts of the voltage, electron affinity, and gap distance on the performance are further analyzed. Results show that the suggested system can achieve high efficiency at the low-temperature cathode. Up to 34.7% of solar-to-electricity efficiency is possible at a cathode temperature of 472.5 K. The proposed model provides a strategy for designing highly efficient thermionic emission devices operating at low temperatures. [ABSTRACT FROM AUTHOR]

Rotating plasma structures, or "spokes," in magnetized discharges characterized by perpendicular electric and magnetic fields have been seen in a growing number of studies and are believed to be the result of gradient-driven drift instabilities. Under certain conditions, we have shown [Ito and Cappelli, Appl. Phys. Lett. 94, 211501 (2009)] the spoke's rotation to be opposite to the E × B direction, i.e., retrograde in its expected direction. Recently [Marcovati et al., J. Appl. Phys. 127, 223301 (2020)], we have linked such counter-intuitive rotation to a local inversion of the electric field. Here, we give further experimental evidence for this inversion and attempt to provide an explanation for a relatively distinct transition seen between retrograde and positive (prograde) drift. In the experiments, a partially magnetized plasma forms inside a magnetron device of ≈ 10 mm radius operated with argon. Discharge current–voltage measurements are acquired for a range of argon fill pressure and inter-electrode spacing. We find two branches of operation—a low current branch of negative resistance, coinciding with the retrograde spoke rotation, and a higher current branch of positive resistance, coincident with prograde spoke rotation. We postulate that at low discharge currents, high magnetic field confinement leads to a large density gradient, causing more electron transport to the anode than that demanded by the external circuit. At higher currents, anomalous axial electron transport (across the magnetic field lines) becomes dominant, eliminating the conditions for field inversion. The current thresholds for the field inversion are found to be sensitive to the argon pressure and inter-electrode spacing. [ABSTRACT FROM AUTHOR]

Different from conventional ferromagnetic methods, producing a spin-polarized current through electrical ways in spintronic devices can greatly increase operating speed, reduce power consumption, and improve device integration. Inspired by recent experimental progress on the synthesis of a heptauthrene molecule, we investigate its spin-dependent transport contacted with Au electrodes through first-principles calculations. By applying a gate voltage, the transmission can be switched between completely spin-up and spin-down polarized states, achieving an electrically controlled dual-spin filter. Furthermore, a fine tuning on the spin polarization, between 100% and − 100%, can also be realized, where the transport with any ratio of spin-up to spin-down electron quantities can be realized beyond the traditional devices. The peculiar transmission spectra and their shift are found to play crucial roles, where transmission peaks distribute on both sides of the Fermi level with opposite spin components. Such a spin-polarization modulating effect is found to be robust to the molecule-electrode contacting site, indicating it is an intrinsic feature of such systems. Moreover, the dimension of the device is at the single-molecule level, suggesting great application potential. [ABSTRACT FROM AUTHOR]

All-solid-state electric double-layer (EDL) thin-film transistors (TFTs) consisting of solution-processed LaZrO gate insulators and sputtered InO channels with thicknesses of 10–200 nm were prepared, and their microstructures and electrical properties were investigated. In addition, mobility, carrier concentration, and their gate-voltage dependence in the InO layer were analyzed during a transistor operation to clarify the electron transport properties. It was confirmed that LaZrO was amorphous and that InO crystallized and had an In2O3 bixbyite structure. The transfer conductance increased with the InO thickness, and its normalized value was maximized (3.6 mS/V) at an InO thickness of 200 nm. The maximum capacitance of LaZrO was 31 μF/cm2, strongly suggesting the formation of an EDL. Solid EDL-TFTs operated stably without deterioration at gate voltages up to 5 V, which usually degrade liquid-electrolyte EDL transistors via electrolysis. Assuming the formation of a 1-nm-thick EDL, the concentration of carrier electrons induced during the transistor operation was estimated to be 1019–1021 cm−3. Moreover, the mobility increased with the InO thickness and reached a maximum value of 68 cm2/(V s) at an InO thickness of 120 nm. The conduction electrons were significantly affected by grain boundary scattering and surface scattering, in addition to scattering within the crystal grain. An increase in the InO thickness, which improved the crystallinity in the crystal grain, reduced the barrier height and the effect of grain boundary scattering. [ABSTRACT FROM AUTHOR]

In this work, we have made experimental measurements of multiple-hump total electron emission yield (TEEY) curves on SiO2 thin films. A Monte-Carlo electron transport model, published in Gibaru et al., J. Electron Spectrosc. Relat. Phenom. 261, 147265 (2022), has been developed to analyze the physical reasons of such atypical behavior. It is shown that the multiple-hump TEEY curves of thin dielectric layers are due to internal recombination effects. However, such kind of phenomenon is demonstrated to be strongly correlated to the incident current density. This analysis reveals that the double-hump TEEY curves observed commonly on insulators are also most probably a measurement artifact, tied to the operating parameters of the electron gun. A careful choice of experimental parameters can eliminate this artifact, by using a constant current density that is also low enough to limit recombination effects. [ABSTRACT FROM AUTHOR]

Partially magnetized low-temperature plasmas (LTP) in an E × B configuration, where the applied magnetic field is perpendicular to the self-consistent electric field, have become increasingly relevant in industrial applications. Hall thrusters, a type of electrostatic plasma propulsion, are one of the main LTP technologies whose advancement is hindered by the not-fully-understood underlying physics of operation, particularly, with respect to the plasma instabilities and the associated electron cross field transport. The development of Hall thrusters with unconventional magnetic field topologies has imposed further questions regarding the instabilities' characteristics and the electrons' dynamics in these modern cross field configurations. Accordingly, we present in this effort a detailed parametric study of the influence of three factors on the plasma processes in the radial-azimuthal coordinates of a Hall thruster, namely, the magnetic field gradient, secondary electron emission, and plasma number density. The studies are carried out using the reduced-order particle-in-cell code developed by the authors. The setup of the radial-azimuthal simulations largely follows a well-defined benchmark case from the literature in which the magnetic field is oriented along the radius, and a constant axial electric field is applied perpendicular to the simulation plane. The salient finding from our investigations is that, in the studied cases corresponding to elevated plasma densities, a long-wavelength azimuthal mode with the frequency of about 1 MHz is developed. Moreover, in the presence of strong magnetic field gradients, this mode results from an inverse energy cascade and induces a significant electron cross field transport as well as a notable heating of the ions. [ABSTRACT FROM AUTHOR]

Quantum dot light-emitting devices (QLEDs) are potential candidates for lighting and display applications. The charge transport mechanism which plays an essential part in the performance of these devices, however, needs to be explored and analyzed for further improvement. The imbalance of the injection and transport of charge carriers within the device adversely affects the efficiency and stability of the device. Charge balance can be improved by better charge injection of holes while suppressing the excessive electrons. A simple and effective strategy to achieve this is using double transport layers or doped transport layers to modulate the band alignment and injection of charge carriers. Here, we propose a new structure and investigate the physical processes within a QLED with a double hole transport layer for improved charge injection of holes and a doped electron transport layer for controlled charge injection of electrons. We find that the process of charge injection, tunneling, and recombination is significantly improved within the quantum dot layer and a better charge balance is achieved in the emissive layer. Through the theoretical simulation model, useful results are obtained which pave the way for designing high-performing QLEDs. [ABSTRACT FROM AUTHOR]

Monte Carlo statistical ray-tracing methods are commonly employed to simulate carrier transport in nanostructured materials. In the case of a large degree of nanostructuring and under linear response (small driving fields), these simulations tend to be computationally overly expensive due to the difficulty in gathering the required flux statistics. Here, we present a novel Monte Carlo ray-tracing algorithm with computational efficiency of at least an order of magnitude compared to existing algorithms. Our new method, which is a hybrid of the analytical Boltzmann transport equation and Monte Carlo used a reduced number of ray-tracing particles, avoids current statistical challenges, such as the subtraction of two opposite going fluxes, the application of a driving force altogether, and the large simulation time required for low-energy carriers. We demonstrate the algorithm's efficiency and power in accurate simulations in large domain nanostructures with multiple defects. We believe that the new method we present is indeed more robust and user friendly compared to common methods and can enable the efficient study of transport in nanostructured materials under low-field steady-state conditions. [ABSTRACT FROM AUTHOR]

Nanostructured negative electron affinity GaAs photocathodes for a polarized electron source are studied using finite difference time domain optical simulation. The structures studied are nanosquare columns, truncated nanocones, and truncated nanopyramids. Mie-type resonances in the 700–800 nm waveband, suitable for generation of polarized electrons, are identified. At resonance wavelengths, the nanostructures can absorb up to 99% of the incident light. For nanosquare columns and truncated nanocones, the maximum quantum efficiency (QE) at 780 nm obtained from simulation is 27%, whereas for simulated nanopyramids, the QE is ∼21%. The high photocathode quantum efficiency is due to the shift of Mie resonance toward the longer wavelength, leading to increased light absorption. The field profile distribution shows the excitation of dipole and quadrupole modes within the nanostructures at resonant frequencies. This leads to enhanced photoabsorption and photoelectron generation closer to emission surfaces than for a flat photocathode. The enhanced photoabsorption and reduced electron transport distance for the nanostructured photocathode enhance its QE compared to that for the flat surface wafer. [ABSTRACT FROM AUTHOR]

β -Gallium oxide (Ga 2 O 3) is an extensively investigated ultrawide-bandgap semiconductor for potential applications in power electronics and radio frequency switching. The room temperature bulk electron mobility (∼ 200 cm 2 V − 1 s − 1 ) 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– 2 × 10 7 cm s − 1 (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. [ABSTRACT FROM AUTHOR]

High-quality single-crystalline multiterminal tungsten nanostructures were fabricated on MgO/GaAs (001) substrates using subtractive lithography. Single-crystalline tungsten films with a thickness of d = 80 nm and low roughness were grown using sequential epitaxy of MgO (001) and W (001) layers on GaAs (001) via pulsed laser deposition. The temperature dependence of bridge-type nanostructure electron conductivity indicates that they are high-quality metal conductors. The electron mean free path reached 760 nm at low temperatures and was approximately an order of magnitude greater than the tungsten film thickness. Strong non-local effects resulting from ballistic electron transport were observed in the multiterminal cross-type W (001) nanostructures with an arm width Wc = 400 nm below T = 80 K. Such effects can be explained by the exponential damping of ballistic properties of nanostructures as a function of the electron mean free path in the wide temperature range 4.2–100 K. Simulations predict that the ballistic effects in such nanostructures can be significant even at room temperature with an arm width approaching 10 nm and a size ratio of Wc/d ∼ 1. [ABSTRACT FROM AUTHOR]

This work performs a numerical study of electron transport through the fundamental logic gate in valleytronics—a valley valve consisting of two or increasing number of valley filters. Various typical effects on the transport are investigated, such as those due to interface scattering, long- and short-range impurity scattering, edge roughness, strain, inter-filter spacing, or increasing number of valley filters. For illustration, we consider the class of specific valves built from graphene quantum wire valley filters in single layer or bilayer graphene, with the filters subject to separate control of in-plane, transverse electric fields. The nearest-neighbor tight-binding model of graphene is used to formulate the corresponding transport problem, and the algorithm of the recursive Green's function method is applied to solve for the corresponding transmission coefficient. In the case of two-filter valves, the result explicitly demonstrates the existence of a pronounced on-off contrast in electron transmission between the two configurations of valves, namely, one with identical and the other with opposite valley polarities in the two constituent filters. The contrast is shown to be enhanced when increasing the number of filters in valves. Signatures of Fano–Fabry–Pérot type resonances in association with interface scattering and inter-filter spacing are illustrated. Electron backscattering due to impurities is found to be sizably suppressed, with the valve performance showing considerable robustness against edge roughness scattering. On the other hand, the presence of a uniaxial strain modifies the electron transmission and results in an interesting quasi-periodic modulation of transmission as we vary the strain strength. [ABSTRACT FROM AUTHOR]

We systematically studied the intrinsic electron transport of the recently fabricated two-dimensional (2D) monolayer MoSi2N4 and WSi2N4 (belong to the MA2Z4 family, where M is a transition metal; A is Si or Ge; and Z is N, P, or As) by using the Boltzmann transport theory with the scattering rates calculated from first-principles calculations. It is found that both materials have moderate room temperature electron mobility of 87 cm2/V s for MoSi2N4 and 119 cm2/V s for WSi2N4. Our detailed analysis shows that their electron mobility difference is attributed to the different average effective mass. Moreover, by comparing studies with monolayer MoS2 and WS2, we reveal that the polar optical phonon pattern of MoSi2N4 and WSi2N4 is governed by the antiparallel silicon–nitrogen bond oscillation, different from MoS2 and WS2, in which is governed by the antiparallel transition metal–sulfur bond oscillation. This feature is arising from the large electronegativity difference between N and Si. Nitrogen has the fourth largest electronegativity, so it always tends to attract plenty of electrons from Si and thus Si has a large Born effective charge, thereby resulting in strong Fröhlich interaction. We further found that all the 2D semiconducting MA2Z4 have large Born effective charges, thereby indicating a generally strong electron–phonon coupling strength. [ABSTRACT FROM AUTHOR]

The McKelvey–Shockley (McK–S) flux method is a semi-classical transport theory that captures ballistic and non-equilibrium effects and can treat carrier flow from the nano-scale to the macro-scale. This work introduces a revised formulation of the McK–S flux equations for electron transport, in order to resolve the energy dependence of the fluxes, capture the effect of electric field, and include acoustic/optical phonon scattering. This updated McK–S formalism is validated by simulating electron transport across a finite-length semiconductor under the influence of a constant electric field under varying conditions, from ballistic to diffusive and from near-equilibrium to non-equilibrium, and benchmarked against solutions of the Boltzmann transport equation (BTE). The McK–S results display good agreement with those of the BTE, including the directed fluxes and heating profiles, with the electron density showing larger differences when far from equilibrium. Compared to other more rigorous techniques, the McK–S flux method is physically intuitive and computationally efficient and, thus, well suited to treat systems that are complex and/or span multiple length scales. [ABSTRACT FROM AUTHOR]

We systematically studied the intrinsic electron transport of the recently fabricated two-dimensional (2D) monolayer MoSi2N4 and WSi2N4 (belong to the MA2Z4 family, where M is a transition metal; A is Si or Ge; and Z is N, P, or As) by using the Boltzmann transport theory with the scattering rates calculated from first-principles calculations. It is found that both materials have moderate room temperature electron mobility of 87 cm2/V s for MoSi2N4 and 119 cm2/V s for WSi2N4. Our detailed analysis shows that their electron mobility difference is attributed to the different average effective mass. Moreover, by comparing studies with monolayer MoS2 and WS2, we reveal that the polar optical phonon pattern of MoSi2N4 and WSi2N4 is governed by the antiparallel silicon–nitrogen bond oscillation, different from MoS2 and WS2, in which is governed by the antiparallel transition metal–sulfur bond oscillation. This feature is arising from the large electronegativity difference between N and Si. Nitrogen has the fourth largest electronegativity, so it always tends to attract plenty of electrons from Si and thus Si has a large Born effective charge, thereby resulting in strong Fröhlich interaction. We further found that all the 2D semiconducting MA2Z4 have large Born effective charges, thereby indicating a generally strong electron–phonon coupling strength. [ABSTRACT FROM AUTHOR]

We use a multi-scale modeling to study the time-dependent dielectric breakdown of an amorphous (a-) HfO 2 insulator in a metal–oxide–metal capacitor. We focus on the role played by electron injection in the creation of oxygen vacancies, which eventually form the percolation path responsible for dielectric breakdown. In this scenario, the electron transport through the dielectric occurs by multi-phonon trap assisted tunnelling (MPTAT) between O vacancies. Energy parameters characterizing the creation of oxygen vacancies and the MPTAT process are calculated using density functional theory employing a hybrid density functional. The results demonstrate that the formation of neutral O vacancies facilitated by electron injection into the oxide represents a crucial step in the degradation process dominating the kinetics at common breakdown fields. We further show the importance of the so-called "energetic correlation" effect, where pre-existing O vacancies locally increase the generation rate of additional vacancies accelerating the oxide degradation process. This model gives realistic breakdown times and Weibull slopes and provides a detailed insight into the mechanism of dielectric breakdown and atomistic and electronic structures of percolation paths in a-HfO 2. It offers a new understanding of degradation mechanisms in oxides used in the current MOSFET technology and can be useful for developing future resistive switching and neuromorphic nanodevices. [ABSTRACT FROM AUTHOR]

The advent of high-power Hall thrusters and the increasing interest toward their use as a primary propulsion system for various missions have given a new boost to the efforts aiming at self-consistent predictive modeling of this thruster technology. In this article, we present a novel approach, which allows enhancing the predictive capability of one-dimensional particle-in-cell (PIC) simulations to self-consistently capture the wave-induced electron transport due to the azimuthal instabilities in Hall thrusters. The so-called "pseudo-2D" PIC scheme resulting from this approach is extensively tested in several operating conditions. The results are compared against a well-established 2D3V axial–azimuthal reference case in terms of the axial profiles of the time-averaged plasma properties, the azimuthal electric field fluctuations and their dispersion features, and the contributions of the force terms in the electron azimuthal momentum equation to the cross-field mobility. We have demonstrated that the pseudo-2D PIC provides a prediction of the above aspects that compares very closely in almost all conditions with those from the full-2D simulation. In addition, the sensitivity of the pseudo-2D simulation results to the numerical parameters associated with our approach is assessed in detail. The outcomes of these analyses have casted light on the next steps to further improve the approach. [ABSTRACT FROM AUTHOR]

Research of lead-free perovskite solar cells (PSCs) has gained attention with an urgent intent to eliminate toxic lead in perovskite materials. The prime intention of this research is to supplement the current research progress with a comparative analysis of various lead-free PSCs through numerical simulation analysis using solar cell capacitance simulator (SCAPS)-1D software. Lead-based toxicity and instability have been one of the major hurdles in restricting perovskite solar cells from being commercialized. This study caters in substituting the need for toxic lead (Pb)-based PSCs with more efficient Pb-free PSCs. The device simulation is carried out in the n-i-p configuration of FTO/[6,6]- phenyl-C61-butyric acid methyl ester/perovskite layer/poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine/Au using six distinct Pb-free perovskites. The impact of various active layers, including hole and electron transport thicknesses and the concentration of doping on solar device performances, has been minutely probed and optimized. CsSnI3 based PSC shows the best power conversion efficiency of 28.97% among all Pb-free devices. This makes very evident its probability to achieve high-performance Pb-free solar devices experimentally at par with lead-based perovskite solar cells in future research. [ABSTRACT FROM AUTHOR]

Atomistic determination of carrier scattering properties is essential for designing nano-electronic devices in two-dimensional (2D) materials. Traditional quantum scattering theory is developed in an asymptotic limit, thus making it inapplicable for 2D materials and heterostructures. Here, we introduce a new paradigm of non-asymptotic quantum scattering theory to obtain the carrier scattering properties at finite distances from active scattering centers. We develop an atomistic multiscale formalism built on the k = p Hamiltonian, supplemented with parameters from first-principles electronic structure calculations. We apply this framework to investigate electron transport in lateral transition-metal dichalcogenide heterostructures and demonstrate enhanced high mobility of the order of 103 cm2 V-1 s-1 at room temperature. The non-asymptotic quantum scattering formalism provides a new frontier to design high-performance mesoscopic devices in 2D materials. [ABSTRACT FROM AUTHOR]

Secondary electron yield (SEY) modeling of Ni(110) surface has been carried out with and without the inclusion of wavevector-dependent harmonic corrections (which alter both the inelastic mean free path and stopping power) and is compared to available experimental data. The correction is shown to improve predictions of the inelastic electron mean free path in Ni and yield better agreement with experimental SEY data. It is found that the SEY is strongly dependent on the presence of adsorbates on surfaces. An increase of hydrogen on the surface, for example, is predicted to result in a significant enhancement in the secondary electron yield, with the positional placement of hydrogen layers on or near the Ni surface influencing the SEY. Using first-principles calculations, the permittivities work function and adsorption energy of various Ni systems have also been calculated, and have shown to compare favorably with available experimental data, and have been used in the present Monte Carlo calculations of electron transport. [ABSTRACT FROM AUTHOR]

MgSnN2 with an average wurtzite structure (wz-MgSnN2) has recently emerged as a pseudo-III-nitride semiconductor, studied for applications in tandem solar cells, green light-emitting diodes, and other optoelectronic devices. This compound has only been researched recently, and, therefore, its charge-carrier transport properties are poorly understood. Understanding these properties is essential for optoelectronic applications. In this study, we grew wz-Mg1−xSn1+xN2 biaxially oriented polycrystalline films with x = −0.08 to 0.29 by reactive sputtering and investigated the charge-carrier transport properties using both direct current and optical techniques. We regarded the wz-Mg1−xSn1+xN2 films as magnesium tin oxynitride films (wz-MTNO) because a certain amount of oxygen was unintentionally incorporated into the sputtered wz-Mg1−xSn1+xN2 films. The wz-MTNO layers were n-type degenerate semiconductors with an electron density (ne) of the order of 1020 cm−3. In films with ne > 8 × 1020 cm−3, optically extracted resistivities (ρopt) obtained via a Drude-fit analysis of the infrared transmittance and reflectance spectra were almost identical to the direct-current resistivities (ρdc), indicating that the contribution of grain boundary scattering to the electron transport was negligible. However, the contribution of grain boundary scattering became unignorable with decreasing ne. The Drude-fit analysis also allowed the determination of the conduction-band effective mass (mc*) for the first time. A band edge mass of mc*/m0 ≈ 0.2 (m0 denotes the free-electron mass) was obtained in the wz-MTNO layers with |x| < 0.1. As x was increased from −0.18 to 0.29, mc*/m0 substantially increased from 0.18 to 0.56, indicating that the conduction-band dispersion decreased. That is, the conduction-band dispersion may be affected by the cation composition x. The findings of this study will provide important information to establish this material as a practical nitride semiconductor. [ABSTRACT FROM AUTHOR]

Plasma structure and electron cross field in the z – θ plane of a Hall thruster E × B plasma under an azimuthally inhomogeneous magnetic field are studied by both experimental and numerical approaches. The work is intended to identify a primary role of electron dynamics on the structure formation by manipulating only the strongly magnetized electrons. The plasma potential distribution shows an axial–azimuthal variation; a low magnetic field region results in spatial potential saturation further downstream. The plasma density structure shows a 1D-like azimuthal variation with less axial deformation. A dense region is observed near the location of ∇ B > --> 0 , where electrons are expected to undergo the ∇ B and curvature drift toward the anode where neutrals are introduced. The potential structure is in close correlation to the Hall parameter distribution, indicating that electron dynamics plays a primary role in plasma structure formation, and via multiple consecutive stepwise physical steps, it eventually affects the density structure formation. In the z – θ space, the cross-field transport by E × B and diamagnetic drifts dominantly determines the electron flow and increases the overall axial electron mobility due to the azimuthal inhomogeneity. It is shown that most of the current is carried by the largest structure, but as the macroscopic structure fades out downstream, small structures grow and share the current. By considering the conservation laws, we show that a relation between azimuthal distributions of physical properties is formed to conserve the axial flux by a balance of specific forces, a balance between the resistive force and the magnetic force in the near-anode region and a balance between the electric/pressure force and the magnetic force in the acceleration and plume region, which differs from the Boltzmann relation satisfied in the radial dimension. Based on this principle, with a simplified test case having a uniform plasma density distribution, we show an analytic relation between azimuthal distributions of the magnetic field and the plasma potential and confirm the relation by a 2D hybrid simulation. [ABSTRACT FROM AUTHOR]

The magnetic field of a magnetron serves to increase the residence time of electrons in the ionization region and thereby enables the discharge to be sustained at low working gas pressures. This hinders the electrons to reach the anode which is necessary to close the electrical circuit. At high atom densities in the ionization region, and in the presence of an electric field, collisions of electrons with heavy species consecutively push electrons across the magnetic field lines, which is known as the classical cross-field transport mechanism. At low atom densities in the ionization region, collisions are rare and the classical cross-field transport mechanism is insufficient to carry the discharge current. This gives rise to plasma instabilities, called spokes, that locally provide pathways for electrons to escape from the near-target region and across the magnetic field lines. Here, we show experimentally, for the case of a high power impulse magnetron sputtering discharge with an aluminum target, how spokes gradually disappear with the increase in local gas density. We present an analytical model that shows that under these high gas density conditions, the classical electron transport mechanism is indeed strong enough to solely carry the discharge current. This highlights the importance of the local gas density in the ionization region for the intensity of spokes in a magnetron sputtering discharge and suggests ways for process optimization. [ABSTRACT FROM AUTHOR]

The effect of keeper geometry on the transport of electrons is investigated experimentally using electrostatic probes in the plume of a hollow cathode. Three keeper configurations—one single orifice and two multiple orifices—were studied. The multiple orifice cases were chosen to examine the influence of the hole-pattern radius while the total exit area and the number of holes remained constant. Two-dimensional maps of the plasma parameters and wave properties were inferred from the probe measurements and were used to evaluate a generalized Ohm's law for the electron flow field. The contributions of pressure, fields, and drag on the transport of electrons were analyzed. The results indicate that increasing the hole-pattern spread reduces the electric field in the plume and increases the pressure contribution to the transport. A further analysis of turbulent wave energy conservation indicates that the multiple orifice keepers increase ion-neutral collisional damping, similar to auxillary flow injection. The implications of these findings on cathode plume modeling and keeper design are discussed. [ABSTRACT FROM AUTHOR]

Cadmium zinc telluride (CZT) is an ideal material for room temperature nuclear radiation detection, but CZT crystals of high quality and low defects concentration are difficult to obtain. Therefore, in order to improve the performance of the CZT detector, the working conditions of the CZT detector could be appropriately changed to make the internal electric field of the CZT detector close to uniform distribution so as to improve the electron transport performance. In this paper, alpha induced transient charge analysis has been used to study the internal electric field of the CZT detector, and deep level defects in CZT were linked with internal electric field distribution. Based on the process, a variety of deep level defects on electron trapping and detrapping by changing the temperature, the output waveform change of charge sensitive preamplifier (the pulse height spectra for alpha radiation at different temperatures) was observed, and then the effects of deep level defects on electron mobility (μ e), electron transport time (T R), the internal electric field, and the electron collection efficiency of the CZT detector were analyzed. The experimental results indicated that the influence of deep level defects was a main factor to the internal electric field in the range of −140 to 40 °C. As the temperature rises, the influence of these defects weakens, μ e and electron collection efficiency both increase, and internal electric field distribution tends to be uniform. Moreover, with the further increasing temperature (−40 to 20 °C), μ e decreased and internal electric field distribution became fluctuating, but electron collection efficiency was basically unchanged, which suggested that the influence of lattice vibration in the range of −40 to 20 °C turned to be the main factor. The above conclusions demonstrated that although the CZT detector has excellent room temperature detection ability, room temperature was not its optimal working temperature due to the influence of high concentration deep level defects. At −20 °C, the CZT detector presented the highest electron collection efficiency and maximum which limited the influence of deep level defects on electron transport, performing the optimal properties. [ABSTRACT FROM AUTHOR]

We develop a theoretical model for thermal conductivity of α -U that combines density functional theory calculations and the coupled electron–phonon Boltzmann transport equation. The model incorporates both electron and phonon contributions to thermal conductivity and achieves good agreement with experimental data over a wide temperature range. The dominant scattering mechanism governing thermal transport in α -U at different temperatures is examined. By including phonon–defect and electron–defect scatterings in the model, we study the effect of point defects including U-vacancy, U-interstitial, and Zr-substitution on the thermal conductivity of α -U. The degradation of anisotropic thermal conductivity due to point defects as a function of defect concentration, defect type, and temperature is reported. This model provides insights into the impact of defects on both phonon and electron thermal transport. It will promote the fundamental understanding of thermal transport in α -U and provide a ground for investigation of coupled electron–phonon transport in metallic materials. [ABSTRACT FROM AUTHOR]

Recently, the long-range spin-selective transport in chiral molecules has been investigated for bio-spintronics. The experimental results for a natural metalloprotein molecule suggested a high spin selectivity. I performed first-principle calculations of electron spin transport in a natural metalloprotein molecule based on the Landauer formula. A gold–metalloprotein–gold device model was used to confirm the high spin polarization. There was a relatively large spin density at some amide groups in the helical peptide structures. Furthermore, a large spin density of iron atoms enhanced the spin density of the neighboring coordinated atoms, resulting in spin polarization in the whole molecule. [ABSTRACT FROM AUTHOR]

Silicon–germanium heterojunction bipolar transistors (HBTs) are of interest as low-noise microwave amplifiers due to their competitive noise performance and low cost relative to III–V devices. The fundamental noise performance limits of HBTs are thus of interest, and several studies report that quasiballistic electron transport across the base is a mechanism leading to cryogenic non-ideal IV characteristics that affect these limits. However, this conclusion has not been rigorously tested against theoretical predictions because prior studies modeled electron transport with empirical approaches or approximate solutions of the Boltzmann equation. Here, we study non-diffusive transport in narrow-base SiGe HBTs using an exact, semi-analytic solution of the Boltzmann equation based on an asymptotic expansion approach. We find that the computed transport characteristics are inconsistent with experiments, implying that quasiballistic electron transport is unlikely to be the origin of cryogenic non-ideal IV characteristics. Our work helps to identify the mechanisms governing the lower limits of the microwave noise figure of cryogenic HBT amplifiers. [ABSTRACT FROM AUTHOR]

Nonlinear interaction between kinetic instabilities in partially magnetized plasmas in the presence of multiply charged ion streams is investigated using kinetic simulations. It was observed by Hara and Tsikata [Phys. Rev. E 102, 023202 (2020)] that the axial ion–ion two-stream instability due to singly and doubly charged ion streams, coupled with the azimuthal electron cyclotron drift instability (ECDI), enhances cross-field electron transport. In the present study, it is observed that the addition of triply charged ions (as a third ion species) contributes to damping of the excited modes, leading to a reduction in the cross-field electron transport. The net instability-driven electron transport is shown to be a function not only of the azimuthal modes, such as the ECDI, but of the multiple ion species that dictate the development of additional plasma waves. It is found that trapping of the higher ion charge states within the plasma waves results in broadening of the ion velocity distribution functions. [ABSTRACT FROM AUTHOR]

Quantum-mechanical calculations of electron transport in ideal graphene nanoribbons show that the transport gap that is predicted by noninteracting theories vanishes if the long-range Coulomb interaction between electrons is taken into account. This is a result of charge screening with the lowest subband edge being pinned to the chemical potential. However, the transport gap reappears if a ribbon is connected to wider leads, which is typically realized in an experimental setup that is based on lithographically patterned graphene ribbons. The gap is determined by scattering at the lead-to-ribbon interface, which can already be captured by the noninteracting theory. [ABSTRACT FROM AUTHOR]

Random alloy fluctuations significantly affect the electronic, optical, and transport properties of (In,Ga)N-based optoelectronic devices. Transport calculations accounting for alloy fluctuations currently use a combination of modified continuum-based models, which neglect to a large extent atomistic effects. In this work, we present a model that bridges the gap between atomistic theory and macroscopic transport models. To do so, we combine atomistic tight-binding theory and continuum-based drift–diffusion solvers, where quantum corrections are included via the localization landscape method. We outline the ingredients of this framework in detail and present first results for uni-polar electron transport in single and multi- (In,Ga)N quantum well systems. Overall, our results reveal that both random alloy fluctuations and quantum corrections significantly affect the current–voltage characteristics of uni-polar electron transport in such devices. However, our investigations indicate that the importance of quantum corrections and random alloy fluctuations can be different for single and multi-quantum well systems. [ABSTRACT FROM AUTHOR]

Transparent conducting Al -doped ZnO films were grown by atomic layer deposition (ALD). Al -doping was introduced by inserting 1 A l 2 O 3 cycle per 28 ZnO cycles. The x-ray photoelectron spectroscopy showed that the density of the Al donors is 2 × 10 21 – 3 × 10 21 cm − 3 , while the Hall-effect measurements showed a ten times lower electron density. This low doping efficiency is a well-known inherent problem of the ALD method, and we wanted to explain its origin. We have found that the electron density is reduced by electron traps at the grain surface; however, the effect was too weak to explain the low doping efficiency. Therefore, the mechanism of the A l 2 O 3 doping was analyzed. We have proposed that each A l 2 O 3 molecule ideally provides two single-electron Al donors accompanied by one Zn vacancy, which acts as a two-electron acceptor. This would cause a perfect compensation; however, the compensation is in reality not perfect, which results in weakly efficient doping. Calculations also showed that each Zn vacancy creates a bound pair with an Al donor. To verify our doping model experimentally, it was inserted into the metallic transport theory and compared with the electron transport measurements. A good agreement was found for a broad range of experimental conditions. In the regime of weak localization, the conductivity showed the temperature dependence σ (T) = a + b T 3 / 4 , which is a signature of weak localization and electron–electron scattering in a 3D dirty metal. [ABSTRACT FROM AUTHOR]