Tunneling Of Charge Carriers Research Articles

The Effect оf Laser Radiation оn Functional Properties of MOS Structures

The electrophysical properties of instrument MOSFET structures (capacitor, field-effect transistor with an isolated gate and an induced channel, CMOS integrated circuit) when exposed to unmodulated laser radiation are studied. Static and dynamic characteristics were measured. The theoretical study was carried out using the developed SPICE models and numerical experiments. An expression is obtained for the volt-ampere characteristic of a field-effect transistor operating in a mode with constant optical illumination. It is shown that the characteristics of the structures are determined by the generation and recombination of nonequilibrium charge carriers, the field effect, the photovoltaic effect in p—n junctions, the photo-Dember effect and tunneling of charge carriers through a gate dielectric. The results of the work are of interest from the point of view of creating high-speed transistors and integrated circuits of a new type.

Low bias charge transport in DNA.

The low-bias current-voltage technique was utilized to study charge transport in single-stranded DNA (ssDNA), assessing the method's effectiveness for future studies aimed at estimating the degree of mutation or DNA damage. In the paper, we showed that charge carrier transfer processes in ssDNA can be precisely monitored using low-bias currents. We used negative differential resistance and the Fowler-Nordheim model to differentiate the charge transport mechanisms observed in a device composed of gold electrode-thiol-ssDNA junctions. It was possible to distinguish the processes at the two junctions (Au/thiol and thiol/DNA) due to their distinct current-voltage characteristics. We observed positive charge carrier tunneling, which we attribute to oxidation and reduction processes in the nucleobases of the ssDNA. Our results suggest that even minor changes in DNA chains can be accurately detected using the described methodology.

Current Density of AlxGa1-xAs/GaAs Superlattice

Theoretically, the AlxGa1-xAs/GaAs superlattice is studied as a function of optical energy with and without bias. The transfer matrix approach has determined the transmission coefficient and resonant tunnelling current density. The number of barriers is estimated at N = 3, and the concentration ratio (the mole fraction value) x at 0.1, 0.2, and 0.3 is fixed. The number of cells in the well is established at (ncw) = 5, while the number of barrier cells (ncb) is changed from 1 to 5 for both biases. This study shows that the change in the number of barrier cells plays a crucial role in the tunnelling of charge carriers and the transmission probability of charge carriers through the depletion regions. Thus, changing the current density is based on the purpose to be applied. In addition, the values ​​of current density at the reverse bias are higher than that in the forward bias, which is explained by the bias controlling the energy levels of the superlattice. It is worth noting that there are many practical applications in which this system can be used, including solar cells, detectors, and light-emitting diodes.

Gradual Change between Coherent and Incoherent Tunneling Regimes Induced by Polarizable Halide Substituents in Molecular Tunnel Junctions.

This paper describes a gradual transition of charge transport across molecular junctions from coherent to incoherent tunneling by increasing the number and polarizability of halide substituents of phenyl-terminated aliphatic monolayers of the form S(CH2)10OPhXn, X = F, Cl, Br, or I; n = 0, 1, 2, 3, or 5. In contrast to earlier work where incoherent tunneling was induced by introducing redox-active groups or increasing the molecular length, we show that increasing the polarizability, while keeping the organization of the monolayer structure unaltered, results in a gradual change in the mechanism of tunneling of charge carriers where the activation energy increased from 23 meV for n = 0 (associated with coherent tunneling) to 257 meV for n = 5 with X = Br (associated with incoherent tunneling). Interestingly, this increase in incoherent tunneling rate with polarizability resulted in an improved molecular diode performance. Our findings suggest an avenue to improve the electronic function of molecular devices by introducing polarizable atoms.

Phonon-assisted leakage current of InGaN light emitting diode

We report on the leakage current mechanism in a blue GaN-based light-emitting diode (LED). The device structure was grown by the MOCVD technique on a sapphire substrate. The LED was characterized through various measurements including current-voltage, electroluminescence, and secondary ion mass spectroscopy (SIMS). Capacitance-voltage measurements were employed to calculate the depletion layer thickness at different bias voltages and to analyze the doping profile in the active layer. The reverse temperature-dependent current-voltage measurements were carried out to study the leakage mechanism. The leakage current was explained by phonon-assisted tunneling of charge carriers through deep trap states. The trap energy and density of states were extracted from the application of the introduced model. Cathodoluminescence measurements were performed to evaluate the density of dislocations, which were then compared to x-ray diffraction measurements. The determined value was close to the density of states obtained from the tunneling model.

Exciton interacting with a moiré lattice: Polarons, strings, and optical probing of spin correlations

The ability to create and stack different atomically thin transition metal dichacogenide (TMD) layers on top of each other has opened up a rich playground for exploring new and interesting two-dimensional (2D) quantum phases. As a consequence of this remarkable development, there is presently a need for new sensors to probe these 2D layers, since conventional techniques for bulk materials such as x-ray and neutron scattering are inefficient. Here, we develop a general theory for how an exciton in a TMD monolayer couples to spin and charge correlations in an adjacent moiré lattice created by a TMD bilayer. Virtual tunneling of charge carriers, assumed for concreteness to be holes, between the moiré lattice and the monolayer combined with the presence of bound hole-exciton states, i.e., trions, give rise to an effective interaction between the moiré holes and the exciton. In addition to the Umklapp scattering, we show that this interaction is spin-dependent and therefore couples the exciton to the spin correlations of the moiré holes, which may be in- as well as out-of-plane. We then use our theory to examine two specific examples where the moiré holes form in-plane ferromagnetic or antiferromagnetic order. In both cases, the exciton creates spin waves in the moiré lattice, which we analyze by using a self-consistent Born approximation that includes such processes to infinite order. We show that the competition between magnetic order and exciton motion leads to the formation of a well-defined quasiparticle consisting of the exciton surrounded by a cloud of magnetic frustration in the moiré lattice sites below. For the antiferromagnet, we furthermore demonstrate the presence of the elusive geometric string excitations and discuss how they can be observed via their smoking gun energy dependence on the spin-spin coupling, which can be tuned by varying the twist angle of the moiré bilayer. All these phenomena have clear signatures in the exciton spectrum, and as such our results illustrate that excitons are promising quantum probes providing optical access to the spin correlations of new phases predicted to exist in TMD materials. Published by the American Physical Society 2024

GaAs-on-insulator based vertical heterojunction tunnel FET: proposal and analysis for VLSI circuit applications

This work analyses the Gallium Arsenide (GaAs)-on-insulator based vertical heterojunction tunnel FET with Gallium Antimonide (GaSb) as source material and GaAs as channel/drain material (GaSb/GaAs VTFET) to enhance the performance of the device and is compared with the Silicon-based VTFET. Silvaco Atlas TCAD tool is employed to perform numerical calculations. Tentative fabrication process flow of GaSb/GaAs VTFET is presented. GaSb is a low bandgap material that enhances the tunneling of charge carriers at source-channel heterojunction. GaSb/GaAs VTFET device outperforms Si-based VTFET in terms of electrical performance metrics such as ON-state current (ION), and ION/IOFF increases by a factor of 11 and 270 respectively; whereas OFF-state current (IOFF), subthreshold swing (SS), threshold voltage (VT) and drain-induced barrier lowering (DIBL) reduce by 95.98%, 39.36%, 17.14% and 29.17% respectively. Further, analog/RF and linearity/distortion performance analysis is carried out. GaSb/GaAs VTFET has improved analog/RF performances in terms of cut-off frequency (fT), gain-bandwidth product (GBP), transit time (τ), device efficiency (DE), transconductance frequency product (TFP) and suppressed distortions in compare to Si-based VTFET. Finally, GaSb/GaAs VTFET is evaluated for process variations and designing digital inverter and common source amplifier circuits. The Look-up-table (LUT) based Verilog-A model within the CADENCE tool has been employed to scrutinize the transient responses of inverter and common source amplifier circuits. Unity gain frequency and 3-dB bandwidth obtained for GaSb/GaAs VTFET amplifier are 15 GHz and 5.97 GHz. Therefore, this work presents GaSb/GaAs VTFET’s strong candidature for analog and digital VLSI circuit designing.

Theory of Resonant Tunneling of Charge Carriers within the Framework of the Green’s Function Method and the Biorthogonal Formalism

Theory of Resonant Tunneling of Charge Carriers within the Framework of the Green’s Function Method and the Biorthogonal Formalism

Temperature-dependent electronic, optical, and solar cell device properties of AlAs and AlSb semiconductors and their p-n homojunctions

AlSb and AlAs have attracted renewed interest in recent years as promising photovoltaic (PV) materials due to significant light absorption, eco-friendliness, and low cost. Here, density functional theory (DFT) in combination with the non-equilibrium Green's function method (NEGF) has been used to compute the temperature-dependent PV parameters of nanoscale AlSb and AlAs p-n junction solar cell devices. In particular, the influence of electron-phonon coupling (EPC) and spin-orbit coupling (SOC) on the PV properties of these devices is investigated. Our results highlight the importance of inclusion of EPC in evaluating the ab initio PV properties of p-n junctions at finite temperatures. At non-zero temperatures, the PV parameters can differ significantly compared to those at zero temperature due to phonon-assisted tunnelling of charge carriers across the p-n junction. In particular, the mobility of low-effective-mass carriers at the p-n junction is found to be enhanced by phonon scattering, which in turn results in improved PV transport properties. The short-circuit current (Jsc) at 300 K proved to be 21.7% (16.2%) higher for AlSb (AlAs) than that at 0 K. On the other hand, the open-circuit voltage (Voc) at 300 K proved to be 19.1% (16.7%) lower for AlSb (AlAs) than that at 0 K. Jsc is higher in AlSb than in AlAs due to higher phonon-influenced mobility of low-effective-mass carriers. Overall, our study strongly suggests the importance of inclusion of EPC and hence phonon scattering in the first-principles quantitative determination of PV parameters of solar cells. The estimates obtained in this study may be utilized as input ab initio parameters in continuum-model-based multi-scale simulations of AlSb and AlAs p-n homo-junction solar cells.

Physics based analysis of a high-performance dual line tunneling TFET with reduced corner effects

To improve the DC and analog/HF performance, a novel dual line tunneling based TFET (DLT-ES-TFET) with elevated source and L-shaped pocket is proposed in this manuscript. In DLT-ES-TFET, the elevated top (G1) and extended back (G2) gates overlapping the source region enhance the line tunneling of charge carriers in both vertical and horizontal directions across the source-pocket interface. TCAD-based simulation results reveal that DLT-ES-TFET offers an improvement of ∼47% and ∼54% in average subthreshold swing when it is compared with E-VTSFET and L-TFET, respectively. Furthermore, ON-current in DLT-ES-TFET is also found to be improved by an order of ∼1 as compared to other two devices. In fact, the L-shaped pocket reduces the corner effects caused by the electric filed crowding across source-channel (S-C) interface, which eventually suppresses the OFF-state leakage in the proposed DLT-ES-TFET. Moreover, enhancement in the charge carriers tunneling across S-C interface leads to a huge increment in the transconductance (∼157μs/μm) of DLT-ES-TFET, which further helps in achieving a high cut-off frequency of 12.3 GHz. Next, transient response of DLT-ES-TFET-based resistive load inverter suggests a notable improvement in peak over- and under-shoots along with propagation delay as compared to E-VTSFET and L-TFET. Lastly, interface traps and temperature analysis is also found to be in favor of the proposed DLT-ES-TFET.

Chiral tunneling through double barrier structure in twisted graphene bilayer

The paper discusses the chiral tunneling of charge carriers through double barrier structure in twisted graphene bilayer. The theoretical analysis investigates the transmission probability for various system parameters under both symmetric and asymmetric barrier conditions. The results reveal that the transmission probability of quasiparticles in the K cone is mirror symmetric to that of Kθ cone about φ=0. Furthermore, the study shows that the transmission changes gradually from perfect transmission to perfect reflection in the normal direction by increasing the incident energy and the barrier height, which is different from the case of monolayer and AB-stacked bilayer graphene. It is also found that the double barrier structure remains, only in certain cases, perfectly transparent for normal or near-normal incidence. The chiral nature of the quasiparticles in graphene causes the tunneling to be highly dependent on the direction and also on the double barrier structure. Interestingly, this characteristic provides additional parameter that allows us to tune the electronic properties of the twisted graphene bilayer. Additionally, we found that the transmission exhibits some sharp resonance peaks, the number and amplitude of which depend on the system parameters. Our results provide a better understanding of chiral tunneling in twisted graphene bilayers through double barrier structures, which may thus offer efficient tools to control the transport properties in future graphene-based nanodevices like transistors and photodetectors.

Electrical characteristics assessment and noise analysis of pocket-doped multi source T-shaped gate tunnel FET

A detailed analysis of a novel multi-source T-shaped gate Tunnel FET (MS-TTFET) is presented in this study in order to address the main issues with conventional TFETs. Due to its exceptionally low off-state current (IOFF) and remarkable sub-threshold properties, the tunnel field effect transistor has received a great deal of interest for low standby power applications. The MSR's integration into the SOI platform increases the device's on current, which increases the effective tunnelling area in the middle of the source-channel junctions. An isolator oxide has been added to prevent the source and drain regions from being directly coupled. A SiGe pocket has been suggested at the source and channel junction; silicon-germanium, a low bandgap material which enhances the tunnelling of charge carriers. A T-shaped gate can increase the effectiveness of the tunnel junction in order to limit the lower value of the leakage current. The multi-source regions of the T-shaped gate tunnel field effect transistor can boost the on-state current (ION) by improving tunnel junction areas. The device's ION/IOFF ratio, which is 1013 for our suggested construction, is the standard measure of merit for any device. It is possible to achieve an increased ON current of the order of 10−5 A/μm with a negligible subthreshold swing (SS) of 42 mV/decade. Moreover, the effect of low frequency flicker noise on the device behavior has been investigated.

Direct current conductance and 1/f-noise in cellulose nanofiber–multi-walled carbon nanotube composites for applications in flexible electronic devices

We report on the studies of conduction mechanism, direct current conductance, and 1f-noise of cellulose nanofiber (CNF) and multiwalled carbon nanotube (MWCNT) composites. The composites were characterized by x-ray diffraction, Fourier transform infrared spectroscopy, and field emission scanning electron microscopy. The temperature- and voltage-dependence of the dc conductance Σ were, respectively, probed to investigate the charge transport mechanism and the electrical response of the composite. At room temperature, the increase in Σ with wt. % of MWCNT ϕ showed typical percolation behavior. The Σ−T behavior was fitted to the combination of one-dimensional variable range hopping and the fluctuation-induced tunneling, which were attributed to hopping of charge carriers through 1D MWCNTs and the tunneling of charge carriers between the bundles of MWCNTs, respectively. The non-Ohmic electrical conduction was characterized by the onset voltage V0(T) which scaled with Ohmic conductance Σ0 as V0(T)∼Σ0(T)xT, with xT being the onset exponent increased with ϕ. A scaling description based on the data collapse method was adopted to find the parameters V0(T) and xT. The noise power spectrum SV(f) followed the relation SV(f)∼Vβ with two different power-laws: β1 in the Ohmic and β2 in the non-Ohmic region (β1>β2). Interestingly, this change in power-laws occurs at the same V0(T) obtained from Σ−V curves. A simple model was proposed to explain the noise behavior after V0(T). It is expected that such electrical characterization of CNF-MWCNT nanopaper composite would open up their possibility of application in flexible electronic devices, intelligent networks, sensors, and actuators.

Evidence of Improved Thermal Stability via Nanoscale Contact Engineering in IGZO Source-Gated Thin-Film Transistors

Despite rapidly expanding interest in thin-film source-gated transistors (SGTs), the high-temperature dependence of drain current (TDDC) in devices comprising Schottky source barriers is delaying wide adoption. To reduce this effect, alternative source designs have been theorized. Specifically, introducing additional nanoscale layers at the source contact should facilitate the tunneling of charge carriers at the Fermi energy level with negligible TDDC. Here, we fabricate amorphous In <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\text{2}}$</tex-math> </inline-formula> Ga <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\text{2}}$</tex-math> </inline-formula> ZnO <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\text{7}}$</tex-math> </inline-formula> tunnel-contact SGTs (TC-SGTs) with three times lower TDDC than polysilicon transistors with Schottky contacts. Numerical simulations help elucidate the control mechanisms. We show that the potential profile across the semiconductor in the bulk of the source-gate overlap region determines injection current, and the introduction of a thin interfacial layer at the contact reduces the role of the contact metal work function (WF) in current control and associated temperature effects. This device architecture adds improved thermal stability to the long list of SGT benefits, including low voltage saturation, power-efficient operation, high intrinsic gain, device-to-device uniformity, and robustness to mechanical and electrical stress.

Magnetic, DC Electrical, and Impedance Properties of Zn Doped Yttrium Iron Garnet Nanoparticles

Y3Fe5-xZnxO12 with x = 0; 0.02; 0.04; 0.06; 0.08; 0.1 (YIG) particle materials were fabricated by sol-gel method combined with heat treatment at 900 °C and 1,000 °C with different annealing times (2 h and 5 h) and heating rates (5 °C/min and 2 °C/min). X-ray diffraction patterns show that the obtained samples are single crystalline phases at the condition of an annealing temperature of 900 °C for 5 h and a heating rate of 2 degrees/min. FESEM images of the samples show particle sizes from the submicron to the micrometer. The magnetization of the samples decreases as the doping concentration increases. I-V characteristics and complex impedance spectra at room temperature of samples were measured. The results show that the resistivity value of the doped samples decreases in the range of 5-6 orders in magnitude compared with that of the pure YIG sample. The contribution of the grain boundaries to the impedance was analyzed. The conducting process is explained due to the tunneling of charge carriers across the grain boundary.

Double-Barrier Quantum-Well Structure: An Innovative Universal Approach for Passivation Contact for Heterojunction Solar Cells

The main drawbacks of modern solar-cell technologies are low-quality surface passivation, recombination losses, and carrier selectivity, which limit their efficiency. Therefore, this study proposes an innovative universal approach for a double-barrier two-dimensional (2D) quantum well (QW) passivation structure for solar cells. To this end, c-Si solar cells were examined as model cells. Preliminary investigations (e.g., contact resistance, passivation, and recombination current density) were conducted with a stack of SiOx/nc-Si/SiOx QW on n-type surfaces, and excellent results were obtained with a 30 nm-thick nc-SiOx(n) carrier-selective layer. Furthermore, the effects of different QW thicknesses and doping doses on the surface passivation of such contacts were studied, and the best results were achieved for a 5 nm QW. These QWs also exhibited a low degree of dopant diffusion, which was suppressed by the double SiOx layer. Furthermore, the 2D QW passivation structure with carrier-selective layers, which was denoted as a heterojunction with quantum well (HQW) solar cell, exhibited an excellent passivation improvement and had a lifetime (τeff) of 2746 μs and an implied open-circuit voltage (iVoc) of 736 mV for a 5 nm 2D QW structure. Moreover, a fabricated 5 nm 2D QW-based silicon heterojunction (SHJ) solar cell exhibited an open-circuit voltage (Voc) of 732.5 mV, a short-circuit current density (Jsc) of 39.5 mA/cm2, a fill factor (FF) of 77.95%, and an efficiency (Eff) of 22.55%. To validate these findings, theoretical calculations were performed using the experimental results, which confirmed the resonance tunneling of charge carriers across the 5 nm HWQ structure.

Effects of the variation of doping content and heat treatment condition on the dielectric properties of Ga doped α-Fe2O3 system: A promising low loss magnetoelectric-semiconductor

The ac conductivity and dielectric properties of the α-Fe2-xGaxO3 samples have been studied in the frequency range 1 Hz–5 MHz and in the temperature range of 203 K–503 K. The samples are electrically semiconductor in nature and the dielectric properties are strongly affected by the transformation of magnetic spin order in the hematite structure. The acconductivity curves exhibited nearly constant loss (NCL) regime at the lower temperatures (where antiferromagnetic spin order dominates) and a charge hoping conduction regime dominates at the higher temperatures (where canted ferromagnetic spin order dominates). The samples showed higher electrical conductivity with the increase of Ga content in hematite structure. The features of electrical conductivity and dielectric properties are strongly dependent on the Ga content in hematite structure and also heat treatment condition of the chemical routed samples. The charge conduction mechanism in the α-Fe2-xGaxO3 system is largely controlled by the correlated barrier hopping of charge carriers, whereas the conduction mechanism in the samples with relatively higher Ga content follows the quantum mechanical tunnelling of charge carriers. The present work carried out a detailed analysis on the temperature and frequency dependent behaviour of the electrical conductivity, impedance spectra, electric modulus, dielectric constant and dielectric loss factor in order to extract the information of the contributions of dielectric parameters from grain and grain boundary of the samples and effect of the heat treatment conditions on dielectric properties.

Highly Sensitive MoS2 Photodetectors Enabled with a Dry-Transferred Transparent Carbon Nanotube Electrode.

Fabricating electronic and optoelectronic devices by transferring pre-deposited metal electrodes has attracted considerable attention, owing to the improved device performance. However, the pre-deposited metal electrode typically involves complex fabrication procedures. Here, we introduce our facile electrode fabrication process which is free of lithography, lift-off, and reactive ion etching by directly press-transferring a single-walled carbon nanotube (SWCNT) film. We fabricated Schottky diodes for photodetector applications using dry-transferred SWCNT films as the transparent electrode to increase light absorption in photoactive MoS2 channels. The MoS2 flake vertically stacked with an SWCNT electrode can exhibit excellent photodetection performance with a responsivity of ∼2.01 × 103 A/W and a detectivity of ∼3.2 × 1012 Jones. Additionally, we carried out temperature-dependent current-voltage measurement and Fowler-Nordheim (FN) plot analysis to explore the dominant charge transport mechanism. The enhanced photodetection in the vertical configuration is found to be attributed to the FN tunneling and internal photoemission of charge carriers excited from indium tin oxide across the MoS2 layer. Our study provides a novel concept of using a photoactive MoS2 layer as a tunneling layer itself with a dry-transferred transparent SWCNT electrode for high-performance and energy-efficient optoelectronic devices.

Вольт-амперні характеристики діодів Шотткі на основі гетероструктури графен/n-Si

The authors investigated the electrical properties of graphene/n-Si Schottky diode heterostructures obtained by mechanical exfoliation of graphite to thin-layer graphene in an aqueous solution of polyvinylpyrrolidone as a result of the dynamics of the dispersed graphite mixture under the action of a mechanical blender. The graphene/n-Si structures differed in terms of duration of applying graphene films on n-Si substrates: 5, 10 and 15 min. The temperature of the substrates did not exceed 250°C. The formation of graphene layers was confirmed by the study of Raman scattering spectra in the frequency range of 1000—3250 cm–1, which show G and 2D bands with the features characteristic of low-layer graphene. The dependence of the electrical properties of the investigated surface-barrier graphene/n-Si structures on the duration of sputtering of graphene films was established. It was found that the value of the contact potential difference φk was 1.35, 1.32 and 1.27 V and the series resistance at room temperature was 3.4•106, 3.4•103 and 3.7•103 Ω for structures with the duration of graphene layer deposition 5, 10 and 15 min, respectively. The formation of both forward and reverse currents was dominated by the tunneling of charge carriers through the potential barrier.

Quantum-dot-like electrical transport of free-standing reduced graphene oxide paper at liquid helium temperatures

We present the results of a study of the electrical properties of macroscopic free-standing reduced graphene oxide paper (RGOP) with a 60 % fraction of sp 2 ‑carbons at liquid helium temperatures. Graphene domains form an array of quantum dots that determine material properties. At low temperatures, the electrical conductivity of the RGOP can be described by the model of tunneling of charge carriers through a disordered quasi-2D quantum dot array. In the free-standing RGOP at the temperature of 4.2 K, the charge carriers are localized in the quantum dots due to the Coulomb blockade. The effective localization length (~5–8 nm) of charge carriers coincides with the average size of the sp 2 ‑carbon regions (~6–8 nm). The transfer of charge carriers in the RGOP at liquid helium temperatures occurs due to tunneling between energetically close graphene domains, which are not nearest neighbors in space and are rather far from each other (up to ~100 nm). • Quantum-dot-like charge transfer in macroscopic free-standing RGO paper • Graphene domains array determines electrical properties of macroscopic RGO material. • Strong localization of charge carriers in free-standing RGO paper at low temperatures • Tunneling between energetically close graphene domains that are not nearest neighbors.