Tunneling Current Density Research Articles

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.

Sliding Memristor in Parallel-Stacked Hexagonal Boron Nitride.

Sliding ferroelectricity in 2D materials, arising from interlayer sliding-induced interlayer hybridization and charge redistribution at the van der Waals interface, offers a means to manipulate spontaneous polarization at the atomic scale through various methods such as stacking order, interfacial contact, and electric field. However, the practical application of extending 2D sliding ferroelectricity remains challenging due to the contentious mechanisms and the complex device structures required for ferroelectric switching. Here, a sliding memristor based on a graphene/parallel-stacked hexagonal boron nitride/graphene tunneling device, featuring a stable memristive hysteresis induced by interfacial polarizations and barrier height modulations, is presented. As the tunneling current density increases, the memristive window broadens, achieving an on/off ratio of ≈103 and 2 order decrease of the trigger current density, attributed to the interlayer migration of positively charged boron ions and the formation of conductive filaments, as supported by the theoretical calculations. The findings open a path for exploring the sliding memristor via a tunneling device and bridge the gap between sliding ferroelectricity and memory applications.

Noise reduction by bias cooling in gated Si/Six Ge1−x quantum dots

Silicon–germanium heterostructures are a promising quantum circuit platform, but crucial aspects, such as the long-term charge dynamics and cooldown-to-cooldown variations, are still widely unexplored quantitatively. In this Letter, we present the results of an extensive bias cooling study performed on gated silicon–germanium quantum dots with an Al2O3 dielectric. Over 80 cooldowns were performed in the course of our investigations. The performance of the devices is assessed by low-frequency charge noise measurements in the band of 200 μHz to 10 mHz. We measure the total noise power as a function of the applied voltage during cooldown in four different devices and find a minimum in noise at 0.7 V bias cooling voltage for all observed samples. We manage to decrease the total noise power median by a factor of 6 and compute a reduced tunneling current density using Schrödinger–Poisson simulations. Furthermore, we show the variation in noise from the same device in the course of eleven different cooldowns performed under the nominally same conditions.

Analytical Model of Optical-Field-Driven Subcycle Electron Tunneling Pulses from Two-Dimensional Materials.

We develop analytical models of optical-field-driven electron tunneling from the edge and surface of free-standing two-dimensional (2D) materials. We discover a universal scaling between the tunneling current density (J) and the electric field near the barrier (F): In(J/|F|β) ∝ 1/|F| with β values of 3/2 and 1 for edge emission and vertical surface emission, respectively. At ultrahigh values of F, the current density exhibits an unexpected high-field saturation effect due to the reduced dimensionality of the 2D material, which is absent in the traditional bulk material. Our calculation reveals the dc bias as an efficient method for modulating the optical-field tunneling subcycle emission characteristics. Importantly, our model is in excellent agreement with a recent experiment on graphene. Our results offer a useful framework for understanding optical-field tunneling emission from 2D materials, which are helpful for the development of optoelectronics and emerging petahertz vacuum nanoelectronics.

High Tunneling Electro-Resistance Due to Resonant-Type Tunneling in a Ferroelectric Tunnel Junction (FTJ) with a Composite Barrier

Recently, ferroelectric tunnel junctions (FTJs) have emerged as potential devices for memory sector wherein the tunneling current is used to sense the direction of polarization with a nondestructive reading operation. The tunneling electro-resistance ratio (TER) is the figure of merit of this device. A composite ferroelectric-dielectric barrier is expected to achieve a high TER with enhanced performance. A theoretical modeling of a FTJ with a composite barrier (CB) consisting of a dielectric (SrTiO3) and ferroelectric (BaTiO3) layers is proposed. The potential energy profile and the transmission characteristics of a typical (20Å) SrRuO3/(20Å) SrTiO3/(20Å) BaTiO3/(12Å) Pt FTJ system were extensively studied, for both OFF and ON states. The tunneling current density and TER were computed with the variation of bias as well as with varying ferroelectric layer width. Under electric bias, an asymmetric triangular well develops at the dielectric-ferroelectric interface in its ON state whose effect in producing a resonant-type tunneling and a high tunneling current density in its ON state is explained.

InP-based tunnel junctions for ultra-high concentration photovoltaics.

To enhance the performance of multi-junction photovoltaics, we investigated three different InP-based tunnel junction designs: p++-InGaAs/n++-InP tunnel junction, p++-InGaAs/i-InGaAs-/n++-InP tunnel junction, and p++-InGaAs/i-InGaAs/n++-InGaAs tunnel junction. The p++-InGaAs/i-InGaAs/n++-InGaAs tunnel junction demonstrated a peak tunneling current density of 495 A/cm2 and a resistivity of 9.3 × 10-4 Ωcm2, allowing the tunnel junction device to operate at a concentration over 30000 suns. This was achieved by inserting an undoped InGaAs quantum well at the p++-InGaAs/n++InGaAs junction interfaces, which enhanced its stability within the operating temperature range of multi-junction solar cells. Moreover, the p++-InGaAs/i-InGaAs/n++-InGaAs tunnel junction exhibited the lowest resistance.

Parametric simulations of composite barrier FTJs under external bias at room temperature

A study on a parametrized model of a composite barrier ferroelectric tunneling junction (FTJ), three-interface system with a non-polar dielectric layer, under an external bias voltage, Va, and at room temperature, using Finite Element Method-based simulations, has been performed. The approach involves the Thomas–Fermi model assuming incomplete screening of polarization charges for building the energy barrier profile, and numerically simulates the electron transport through the barrier by bias-voltage-dependent tunneling, using Tsu-Esaki formulation. That naturally includes the temperature dependent contributions to the total current density. The tunneling electroresistance ratio (TER) and current densities are computed considering variations of a large set of parameters that describe the composite barrier system in realistic physical range of values with respect to a reference (prototypical) system. In this study, the parametric simulations were performed starting from selected data reported on the SrRuO3/SrTiO3/BaTiO3/SrRuO3 heterostructure. The most important results of our work can be stated as follows: (i) The simulations prove to be a reliable approach when we are interested in the prediction of FTJ characteristics at temperatures close to 300 K, and (ii) We show that several configurations with large TER values can be predicted, but at the expense of low current densities in the ON state. We suggest that the results may be useful for assessing the FTJ performances at ambient temperature, as well as to design preoptimized FTJs by using different combinations of materials to comply with a set of properties of a specific model.

Electron conduction mechanisms in magnetic tunnel junctions fabricated using amorphous Si-Zn-Sn-O as a low-resistive semiconducting barrier

CoFeB/ Si-Zn-Sn-O /CoFeB magnetic tunnel junctions (MTJs) have been fabricated using amorphous Si-Zn-Sn-O as a low-resistive semiconducting barrier. In the low bias voltage range (up to ∼0.2 V), direct tunneling is found to be the dominant transport mechanism in MTJs. Tunneling conduction is further verified by simulation of tunnel current density and differential conductance using Simmon’s and Brinkmann model, respectively. Simulated results provided valuable insights into the barrier properties, including interfacial barrier height, thickness, and barrier asymmetry. Above the direct tunneling regime, electron transport in MTJs is governed by Pool Frenkel emission, which possibly arises due to the presence of high-density localized tail states below the conduction band of amorphous Si-Zn-Sn-O. Tunnelling magnetoresistance value of MTJs is found to be very low, which is attributed to the presence of various inelastic conduction channels. The results of this study might be useful to explore the potential of amorphous Si-Zn-Sn-O for fabricating low-resistive MTJ based spintronic devices.

Enhanced current density and asymmetry of metal–insulator–metal diodes based on self-assembly of Pt nanoparticles

Metal–insulator–metal (MIM) diodes facilitate rectification at high frequencies. However, the rectification ratio for light from visible to infrared spectra is insufficient. In this study, we developed a MIM diode with a strongly enhanced electric field achieved using the self-assembly of Pt nanoparticles (NPs) via atomic layer deposition. By shaping the tunneling barrier, current density and asymmetry were simultaneously enhanced by several orders of magnitude compared with the symmetric MIM diode. The diode efficiency of the proposed MIM diodes was experimentally demonstrated to be 231 times greater than that of the MIM diode without NPs. This strategy indicates significant potential for high-frequency rectification applicable in optical rectenna.

Dynamics and Modeling of Multidomains in Ferroelectric Tunnel Junction—Part-II: Electrostatics and Transport

We have derived the 2-D analytical multidomain electrostatics model of the ferroelectric tunnel junction (FTJ) in part-I of this work. Here, we have used the 2-D potential functions from part-I to determine the depolarizing energy density of the ferroelectric layer. The coupled solution of the Landau Ginzburg–Devonshire (LGD) equation with Poisson’s equation is obtained to capture the domain texture in the ferroelectric layer. The nucleation and movement of the domain wall are incorporated into the model by minimizing net ferroelectric energy (depolarization energy density + free energy density + gradient energy density). Due to the mathematical complexity, spontaneous polarization <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$({P}_{s})$ </tex-math></inline-formula> and coercive electric field <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$({E}_{c})$ </tex-math></inline-formula> are assumed to be fixed, and the net system energy is minimized only by domain wall nucleation and movement in the ferroelectric layer. The analysis of this article is twofold; first, we study the impact of domain dynamics on electrostatics in an FTJ. Subsequently, the obtained electrostatics is used to study the variations in tunneling current, and ON/OFF ratio [tunnel electroresistance (TER)] originated from multidomain dynamics. We show that ON/OFF tunneling current density and TER varies locally in the ferroelectric region, and approximately one-decade local variations in current density are observed. The optimization techniques to achieve a uniform and maximum TER are also discussed. Furthermore, the impact of the bottom insulator layer on ferroelectric’s gradient energy is also studied.

Crossover from direct to trap assisted Fowler Nordheim (FN) tunneling in CoFeB/MgO/CoFeB magnetic tunnel junctions

Electron conduction mechanisms in CoFeB (0.8–10 nm)/MgO (3 nm)/CoFeB (4.2 nm) magnetic tunnel junctions (MTJs) have been investigated in detail. A clear crossover from direct tunnelling to trap assisted Fowler Nordheim (FN) tunneling is observed with increasing bias voltage in all the pristine MTJs. In contrast, FN-like tunneling is completely suppressed in vacuum annealed MTJs, which plausibly indicates diffused interfaces and enhanced trap state density in the MgO barrier. In annealed MTJs, beyond the direct tunneling regime, bulk-limited Pool Frenkel emission followed by interface-limited Schottky emission are found to be the dominant transport mechanisms. Simulations of tunnel current density J(V) and differential conductance (dJ/dV) of MTJs have been carried out using Simmons (symmetric rectangular barrier) and Brinkman (asymmetric trapezoidal barrier) model, which provides valuable insights into the barrier height and interface property at the MgO/CoFeB interface. Results of this study might be helpful to further improve CoFeB/MgO based MTJs for efficient implementation in sensors and memory devices.

Dynamic molecular tunnel junctions based on self-assembled monolayers for high tunneling current triboelectricity generation

Here, we show a novel energy conversion design with a dynamic MIM structure. This is realized though grafting CF3group which shows high tunnelling current density of up to 7.6 × 106Am−2. This can further fulfill the macroscopic energy harvesting.

High performance p++-AlGaAs/n++-InGaP tunnel junctions for ultra-high concentration photovoltaics.

A p++-AlGaAs: C/n++-InGaP: Te tunnel junction with a record peak tunneling current density of 5518 A/cm2 was developed. This was achieved by inserting a 6.6 Å undoped GaAs quantum well at the junction interface, and the numerical model demonstrated that trap-assisted tunneling contributes to the high peak tunneling current. Furthermore, we found that the p++-AlGaAs: C/n++-InGaP: Si + Te tunnel junctions have lower resistance and better stability than p++-AlGaAs: C/n++-InGaP: Te tunnel junctions in the operating temperature range of the multijunction solar cells, and the peak tunneling current density of the p++-AlGaAs: C/n++-InGaP: Si + Te tunnel junctions excess 3000 A/cm2 with a voltage drop of 7.5 mV at 10000 suns.

Hole‐Selective Ultrathin Al‐Doped SiOxPassivation Layer Formed by Immersing in Aluminum Nitrate Aqueous Solution

Herein, ultrathin Al‐doped SiOxlayer formed by immersing in Al(NO3)3aqueous solution is introduced. This layer enables high‐level surface passivation with a maximum effective surface recombination velocity (Seff,max) &lt; 16 cm s−1at an excess carrier density (Δn) of 1 × 1015 cm−3for 2.5 Ω cm n‐type c‐Si without any other processes such as film deposition in a vacuum chamber, high‐temperature annealing, and hydrogenation. This passivation effect presumably comes from negative fixed charges localized in Al‐doped SiOxlayers, forming inversion layers due to upward Si band bending at the SiOx/Si interface. In addition, the Al‐doped SiOxlayers facilitate accumulated holes at the interface to tunnel through the layers even though the applied bias is extremely low. The high tunnel current density of holes accumulated in the inversion layers implies that these ultrathin Al‐doped SiOxlayers are expected to be favorably implemented for high‐efficiency passivating‐contact c‐Si solar cells.

A Theoretical Model to Predict Contact Electrification

Abstract Triboelectric nanogenerators (TENGs) are widely applied to latest nanogenerators which are based on contact electrification (CE). In order to predict the working process of TENGs effectively, this paper proposes a dynamics model to simulate the dynamic mechanism of CE. Taking Fe and polytetrafluoroethylene (PTFE) as contact materials, the field emission under a strong electric field could occur when the interface distance is small enough. The transferred charges in steady state and the differences of interface barrier are calculated by self-consistent field (SCF) method. The molecular dynamics (MD) simulation is carried out under the contact pressure and electric field. The structure results of MD simulation and the electric fields obtained by SCF calculation are the input parameters for each other which run alternately. According to dynamic interface distances and the differences of interface barrier, the dynamic transferred charges can be finally predicted by tunnel current density. The results reveal that the amounts of transferred electrons are positively corresponded to the external pressure and the energy conversion efficiency will reach the extreme value when the pressure is near 130 MPa.

Quasi-Compact Model of Direct Source-to-Drain Tunneling Current in Ultrashort-Channel Nanosheet MOSFETs by Wavelet Transform

We present an analytical approach for the calculation of direct source-to-drain tunneling (DSDT) probability of electrons in gate-all-around (GAA) silicon nanosheet (SiNS) MOSFETs. The used method is based on the wavelet transform and leads to a quasi-compact model (QCM) for the DSDT current of ultrashort-channel devices. Among them, we introduce a four-piece parabolic approximation method for the conduction band edge and present analytical expressions for the tunneling distances of electrons with different energy levels. The development of a QCM is achieved by limiting the number of interpolation points for the tunneling current density to seven specific electron energies, distributed around the energy level that makes the largest contribution to the tunneling current. A further simplification is achieved by the Gaussian approximation of the tunneling current density in transverse direction so that only the center and surface potentials ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Phi _ {\text {C}}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Phi _ {\text {S}}$ </tex-math></inline-formula> ) at the barrier are of interest for the modeling. For comparison, all those approximations are also implemented in the Wentzel–Kramer–Brillouin (WKB) approximation. Furthermore, the approach is verified by nonequilibrium Green’s function (NEGF) simulation.

Fabrication of High-Quality Josephson Junctions Based on Nb|Al-AlN|NbN

A description of the fabrication technology of high-quality tunnel SIS junctions is presented, with following characteristics: energy gap in superconductors Vg=3.2-3.4 mV, tunnel current density up to J 35 kA/cm2, quality factor Rj/Rn (ratio of subgap resistance to normal-state resistance) up to 30, junction area up to 1 μm2. The SIS junctions are integrated into the NbTiN|SiO2|Al microstrip line. Keywords: superconducting devices, superconductor--insulator--superconductor tunnel junction, plasma etching.

A Modelling of Tunnelling Current through a Trapezoidal Potential Barrier by Using Exponential Wavefunction Approach

A tunnelling current through a trapezoidal barrier potential has been modelled. The transmittance is determined using the exponential wavefunction approach method. Furthermore, the transmittance is used to calculate the tunnelling current density by applying the Gauss-Laguerre quadrature method. The simulation results show the increasing bias voltage causes the raising tunnelling current, and an increase of temperature is proportional to the tunnelling current.

A Modelling of Tunnelling Current through a Trapezoidal Potential Barrier by Using Exponential Wavefunction Approach

A tunnelling current through a trapezoidal barrier potential has been modelled. The transmittance is determined using the exponential wavefunction approach method. Furthermore, the transmittance is used to calculate the tunnelling current density by applying the Gauss-Laguerre quadrature method. The simulation results show the increasing bias voltage causes the raising tunnelling current, and an increase of temperature is proportional to the tunnelling current.

Current—voltage characteristics of connecting tunnel diodes at temperature heating up to 80°C

Investigations of the temperature stability of the peak tunneling current density of connecting tunneling diodes, which are necessary for the creation on their basis of multijunction photoconverters of powerful optical radiation, have been carried out. The structures of n++-GaAs/i-GaAs/i-AlGaAs/p++-AlGaAs of connecting TD with an intermediate undoped layer thickness of 7.5 nm and a growth temperature of 500 °C (structure ”A”) and with a thickness of 10 nm and a temperature of 450 °C (structure ”B”) were investigated. When heated to 80 °C, an increase in the peak tunneling current density of the TD structure ”B” by 4% is observed. However, for structure ”A”, a decrease in the peak tunneling current density by 5% with heating is observed. The factors leading to the appearance of a negative or positive temperature coefficient of the peak tunneling current density are determined using mathematical modeling of tunneling diodes based on GaAs/AlGaAs materials. By reducing the epitaxial growth temperature of n++–GaAs/i-GaAs/i-AlGaAs/p++–AlGaAs tunnel diode structure to 450 °C and including an undoped i-layer 10 nm thick between the degenerate layers ensure the temperature stability of peak current density when heated to 80 °C.