Resonant Tunneling Research Articles

Compact modeling of Schottky barrier field-effect transistors at deep cryogenic temperatures

In this paper, a physics-based DC compact model for Schottky barrier field-effect transistors at deep cryogenic temperatures is presented. The model uses simplified tunneling equations at temperatures of ϑ≈0K in order to calculate the field emission injection current at the device’s Schottky barriers. Additionally, an empirical expression for including resonant tunneling effects is introduced. The compact model is also compared to and verified by measurements performed on ultra-thin body and buried oxide SOI Schottky barrier field-effect transistors and is able to capture the signature of resonant tunneling effects in the transfer characteristics.

2-D tunneling structures and increased peak to valley current ratio in double barrier quantum systems under perpendicular electric and magnetic bias

Tunneling across an electrically biased double barrier system (with potential V along the z-axis) in a transverse magnetic field B (along the x-axis) is studied. The magnetic field-induced coupling of the transverse momentum (ky) with the z-direction motion of the electron selects the minimum value of ky depending on the incident energy εz below which the wave becomes evanescent in nature and is restricted from participating in the tunneling process. With the increase in B, resonant tunneling across the DBS occurs for an increasing range of resonant energy εzr albeit at a particular transverse momentum kyr for each εzr. Thus, the one-dimensional resonant tunneling feature at the quasi-resonant energy εzr0 for the entire spectrum of ky in absence of the magnetic field changes to a two-dimensional resonance structure in the εy and εz plane with the application of the magnetic field. The lower and upper bound of εzr and the corresponding limits on kyr for resonant tunneling based on B and V is spelt out. A formula for current density based on these observations is developed and the current–voltage relation for the DBS in presence of the transverse magnetic field is studied. With the application of the magnetic field the Peak to Valley current ratio (PVCR) calculated on the basis of tunneling current increases by many folds. The effect of Zeeman splitting due to interaction of spin moment of conduction electrons with magnetic field on the tunnel current is discussed.

Calculating InN/GaN Transmission Coefficient from Single Barrier to Five Barriers with Propagation Matrix and Transfer Matrix Methods

In this study, the value of transmission coefficient on InN/GaN semiconductor from a single barrier to five barriers was determined by using the propagation matrix method and the transfer matrix method. This study aims to see the effect of adding a barrier to the number of resonance tunneling that occurs, to see the difference in transmission coefficient values which was obtained with the two methods, and to determine the effectiveness of the program execution process time from the propagation matrix and transfer matrix methods using Matlab programming. The results obtained indicated that the value of the transmission coefficient obtained from the two methods was the same. As the number of barriers increases, the number of resonance tunneling that occurs will increase. These two matrix methods had differences in terms of the effectiveness of the program execution process time and calculation process. The propagation matrix method was considered more effective than the transfer matrix method.

Multiple Fano Resonances in Dynamic Resonant Tunneling Processes

The existence of Fano resonances in dynamic resonant tunneling (RT) systems has been investigated. Fano resonances are characterized by the appearance of a 100% reflection coefficient in proximity to a high transmission coefficient. For a Fano resonance to appear, a bound state must exist. On the other hand, a resonant tunneling process is characterized by a high transmission and the existence of a quasi-bound state (QBS) instead of a bound one. It has been shown that, by narrowing the width of the barrier, the resonance energy of the QBS gradually decreases and eventually turns into a bound state. Consequently, in a dynamic RT process, there are two scenarios: either a bound state exists, in which case, Fano resonances exist for any barrier width, or a QBS exists, and the barrier should be narrow enough for the Fano resonance to appear. In both cases, the incoming particle’s frequency must be lower than the oscillating well’s frequency. In this work, these resonances are investigated in detail, and both exactly numerically and approximated analytical expressions are derived for both the weak and strong oscillating amplitude regimes. One of the conclusions is that, when the oscillating frequency is low enough, multiple Fano resonances can appear by varying the barrier’s width. Since these resonances are very sharp and zero transmission can easily be detected, this property can be used as a very accurate method for measuring the barrier’s width, even when the particle’s de-Broglie wavelength is much larger than the barrier’s width.

0D-2D heterostructure for making very large quantum registers using ‘itinerant’ Bose-Einstein condensate of excitons

Presence of coherent resonant tunneling in quantum dot (zero-dimensional) - quantum well (two-dimensional) heterostructure is necessary to explain the collective oscillations of average electrical polarization of excitonic dipoles over a macroscopically large area. This was measured using photo excited capacitance as a function of applied voltage bias. Resonant tunneling in this heterostructure definitely requires momentum space narrowing of charge carriers inside the quantum well and that of associated indirect excitons, which indicates bias dependent itinerant Bose-Einstein condensation of excitons. Observation of periodic variations in negative quantum capacitance points to in-plane coulomb correlations mediated by long range spatial ordering of indirect, dipolar excitons. Enhanced contrast of quantum interference beats of excitonic polarization waves even under white light and observed Rabi oscillations over a macroscopically large area also support the presence of density driven excitonic condensation having long range order. Periodic presence (absence) of splitting of excitonic peaks in photocapacitance spectra even demonstrate collective coupling (decoupling) between energy levels of the quantum well and quantum dots with applied biases, which can potentially be used for quantum gate operations. All these observations point to experimental control of macroscopically large, quantum state of a two-component Bose-Einstein condensate of excitons in this quantum dot - quantum well heterostructure. Therefore, in principle, millions of two-level excitonic qubits can be intertwined to fabricate large quantum registers using such hybrid heterostructure by controlling the local electric fields and also by varying photoexcitation intensities of overlapping light spots.

Characterization of just one atom using synchrotron X-rays.

Since the discovery of X-rays by Roentgen in 1895, its use has been ubiquitous, from medical and environmental applications to materials sciences1-5. X-ray characterization requires a large number of atoms and reducing the material quantity is a long-standing goal. Here we show that X-rays can be used to characterize the elemental and chemical state of just one atom. Using a specialized tip as a detector, X-ray-excited currents generated from an iron and a terbium atom coordinated to organic ligands are detected. The fingerprints of a single atom, the L2,3 and M4,5 absorption edge signals for iron and terbium, respectively, are clearly observed in the X-ray absorption spectra. The chemical states of these atoms are characterized by means of near-edge X-ray absorption signals, in which X-ray-excited resonance tunnelling (X-ERT) is dominant for the iron atom. The X-ray signal can be sensed only when the tip is located directly above the atom in extreme proximity, which confirms atomically localized detection in the tunnelling regime. Our work connects synchrotron X-rays with a quantum tunnelling process and opens future X-rays experiments for simultaneous characterizations of elemental and chemical properties of materials at the ultimate single-atom limit.

Defect formation in InGaAs/AlSb/InAs memory devices

ULTRARAMTM is a novel floating-gate nonvolatile memory in which the oxide barrier of flash is replaced by a triple-barrier resonant tunneling structure comprising of multiple InAs/AlSb heterojunctions. The quality of the triple barrier resonant tunneling heterostructure of an ULTRARAMTM device in terms of interface sharpness and the presence of defects was analyzed by cross-sectional scanning tunneling microscopy. We observed two different types of defects: stacking faults originating in the layers below the triple barrier resonant tunneling structure and AlSb accumulations at the interface between the lower AlSb layer of the triple barrier resonant tunneling structure and the InGaAs channel. The InGaAs surface of a second sample was measured by atomic force microscopy in order to investigate whether its unevenness is caused by deposition of the AlSb layer or it is already present before the AlSb deposition process.

Electrical solitary waves on a transmission line periodically loaded with resonant tunneling diodes using some different methods

Electrical solitary waves on a transmission line periodically loaded with resonant tunneling diodes using some different methods

Speed limitations of resonant tunneling diode-based photodetectors.

In this work, we study multiple epitaxial layer structures incorporating a resonant tunneling diode photodetector utilizing the In0.53Ga0.47As/InP material system for operation at the near-infrared region of 1.55 and 1.31 micrometers. We study the photodetection speed of response for these devices and the physical limitations affecting their bandwidth. We show that resonant tunneling diode-based photodetectors have bandwidth limitations due to the charge accumulation near the barriers and report on an operating bandwidth reaching up to 1.75 GHz in particular structures, which is the highest number reported for such detectors to the authors' best knowledge.

Large Faraday rotation angle with high transmittance in Weyl semimetal assisted by resonant tunneling

Over the past decades, a series of nanostructures have been proposed to intensively enhance the Faraday rotation angle. However, the mutual inhibition between the Faraday rotation angle and the transmittance poses a challenge to achieve large Faraday rotation angle with high transmittance. In this paper, a sandwich structure consisting of two Weyl semimetal (WSM) layers of the same thickness and a dielectric layer is designed. Empowered by the resonant tunneling, the enhanced Faraday rotation effect is accompanied by an increase in transmittance. In the presence of realistic level of optical loss, the transmittance can be up to reach 97.4% when the resonant tunneling conditions of left-handed and right-handed polarized light are satisfied simultaneously, and its corresponding Faraday rotation angle can also be as high as −51.1 degrees. By adjusting the axial vector of the WSM layer, we design an optical isolator with a transmittance of up to 97% and a Faraday rotation angle of 45 degrees. This simple triple-layer structure provides some theoretical basis and reference value for future research into non-reciprocal devices.

A Comparative Study of Fixing One Barrier Varying Another Barrier for a Resonant Tunneling Diode

In this research paper, effects of fixing one barrier and varying another barrier have been analyzed and compared for a GaAs/Al0.3Ga0.7As based double barrier resonant tunnelling diode for two different models - Hartree Quantum Charge model and semi-classical Thomas Fermi model. VI characteristic graphs are studied to assess the overall performance of both models. The simulations are carried out in a nanoelectronics modelling tool suite – Nano electronic Modelling 5 (NEMO5) considering Non-Equilibrium Green’s Function (NEGF), at room temperature of 300K and biased voltage of 0 to 0.5 V. In this paper, it was demonstrated that a very larger amount of current is supplied by both models when the first barrier is varied and second barrier is fixed in comparison to the first barrier when kept fixed and second barrier is varied. But as quantum charge inside the quantum well is existed in the Hartree model, so overall Hartree model supplied a greater amount of current compared to the Thomas Fermi model. Quantum charge inside its quantum well is not present in the Thomas Fermi model. But a better NDR region is created by the Thomas Fermi model in both varied first barrier-fixed second barrier and fixed first barrier-varied second barrier cases compared to the Hartree model. This NDR region can be used for numerous digital applications. On the other hand, a vast range of analog applications can be used by the Hartree model that produced larger current per unit voltage.

Quantum phase slips in a resonant Josephson junction

We investigate the consequences of resonant tunneling of Cooper pairs on the quantum phase slips occurring in a Josephson junction. The amplitude for quantum tunneling under the Josephson potential barrier is modified by the Landau-Zener amplitude of adiabatic passage through an Andreev level crossing, resulting in the suppression of $2\pi$ phase slips. As a consequence, close to resonance, $4\pi$ phase slips become the dominant tunneling process. We illustrate this crossover by determining the energy spectrum of a transmon circuit, showing that a residual charge dispersion persists even at perfect transparency.

Terahertz Oscillator Chips Backside-Coupled to Unclad Microphotonics

Terahertz technology is largely dependent upon planar on-chip antennas that radiate downwards through the substrate, and so an effective means to interface these antennas with integrated waveguides is an attractive prospect. We present a viable methodology for backside coupling between a terahertz oscillator chip and a broadband all-intrinsic-silicon dielectric waveguide. Our investigation employs resonant tunneling diodes as compact two-terminal electronic terahertz oscillators, and terahertz waves are observed from 270 GHz to 404 GHz. The fact that this power is accessed via a curved length of silicon waveguide validates successful backside coupling.

Ferroelectric Tunnel Junction Based on Asymmetric Barrier–Well–Barrier Structure: The Role of Resonant Tunneling

An innovative resonant ferroelectric tunnel junction (FTJ) based on asymmetric barrier–well–barrier structure is theoretically proposed. It is achieved by metal–ferroelectric–dielectric–dielectric–metal (M-F-I <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\text{1}}$</tex-math> </inline-formula> -I <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> -M) stack, where a low-barrier dielectric I <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\text{1}}$</tex-math> </inline-formula> is inserted to form a quantum well. Physical modeling of self-consistent potential and carrier transport is established to bridge the polarization reversal and resonant tunneling (RT). The resonant FTJ shows improved ON-current and ON/OFF tunneling electroresistance (TER) ratio while maintaining a relatively low depolarization field. Compared with FE-HfO <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> /SiO <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> or FE-HfO <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> /Ta <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> O <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\text{5}}$</tex-math> </inline-formula> bilayer FTJs, the resonant FTJ using FE-HfO <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> /Ta <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> O <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\text{5}}$</tex-math> </inline-formula> /HfO <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> stack exhibits a larger TER ratio by several orders of magnitude, which can be further enhanced using FE-HfO <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> /Ta <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> O <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\text{5}}$</tex-math> </inline-formula> /SiO <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> stack. The underlying physics is attributed to the RT, of which contribution to TER effect is qualitatively and quantitatively analyzed. The resonant band engineering, through enhancing the device asymmetry, including the geometry asymmetry and the material asymmetry, is to shift the resonance peak close to or away from the Fermi energy depending on the polarization direction. This work is useful for FTJ design for large array circuit applications.

Experimental Characterization of Resonant Tunneling Chaos Generator Circuits in Microwave Frequency Range

Experimental Characterization of Resonant Tunneling Chaos Generator Circuits in Microwave Frequency Range

Unraveling the decarboxylation dynamics of the fluorescein dianion with fragment action spectroscopy

The decarboxylation dynamics of the doubly deprotonated fluorescein dianion, Fl2-, are investigated by recording fragment action spectra for the anion, Fl-, and its decarboxylated analog, Fl-CO2-, using a new reflectron secondary mass spectrometer. The formation of the anion, Fl-, is directly investigated by photoelectron imaging. The Fl- and Fl-CO2- action spectra indicate that, for λ < 400nm, one-photon dissociative photodetachment, i.e., simultaneous decarboxylation and electron loss, competes with photodetachment, whereas for λ > 400nm, decarboxylation only proceeds following electron loss via a sequential two-photon process. The primary decarboxylation pathway is the ready loss of CO2 from the relatively short-lived intermediate excited state, Fl-[D1], which is formed by electron loss from the dianion via resonant tunneling through the repulsive Coloumb barrier associated with a high-lying excited dianion state, Fl2-[S2].

Orbital and Skeletal Structure of a Single Molecule on a Metal Surface Unveiled by Scanning Tunneling Microscopy.

Atomic-scale spatial characteristics of a phthalocyanine orbital and skeleton are obtained on a metal surface with a scanning tunneling microscope and a CO-functionalized tip. Intriguingly, the high spatial resolution of the intramolecular electronic patterns is achieved without resonant tunneling into the orbital and despite the hybridization of the molecule with the reactive Cu substrate. The resolution can be fine-tuned by the tip-molecule distance, which controls the p-wave and s-wave contribution of the molecular probe to the imaging process. The detailed structure is deployed to minutely track the translation of the molecule in a reversible interconversion of rotational variants and to quantify relaxations of the adsorption geometry. Entering into the Pauli repulsion imaging mode, the intramolecular contrast loses its orbital character and reflects the molecular skeleton instead. The assignment of pyrrolic-hydrogen sites becomes possible, which in the orbital patterns remains elusive.

Hydrogenated cove-edge aluminum nitride nanoribbons for ultrascaled resonant tunneling diode applications: a computational DFT study

While synthesizing quasi-one-dimensional nanoribbons, there is a finite probability that edges have cove-edge defects. This paper focuses on the structural, electronic, and transport properties of cove-edge aluminum nitride nanoribbons (AlNNR) using density functional theory and the non-equilibrium Green’s function (NEGF) method. The cove-edge AlNNRs are thermodynamically stable and exhibit metallic behavior. Interestingly, the calculated current–voltage characteristics of the cove-edge AlNNR-based nanodevices show negative differential resistance (NDR). The H-AlN-Cove nanodevice exhibits high peak-to-valley current ratio (PVCR) of the order of 107. The calculated PVCR of the H-AlN-Cove nanodevice is 106 times higher than that of the silicene nanoribbon (SiNR) and graphene nanoribbon (GNR), and 104 times higher than that of the phosphorene nanoribbon (PNR) and arsenene nanoribbons (ANR)-based devices respectively. The NDR feature with high PVCR provides a prospect for the cove-edge AlNNR in nanodevice applications.

A study of tunneling in triangular resonant tunnel diodes: Effect of barrier width, barrier height, pressure, temperature, and heterostructure strain

Using the transfer matrix, the transmission coefficient of electrons is examined in the triangular double-barrier semiconductor heterostructure. GaAs-based heterostructure is considered to study the role of barrier width, barrier height, pressure and temperature. The geometrical parameters of the heterostructures (barrier width and barrier height) and the external perturbation (pressure and temperature) influence the tunneling properties. The tunneling time of the electrons is also studied using Heisenberg's uncertainty principle. The account of the heterostructure strain is also discussed.

Enhancement of nonvolatile memory characteristics caused by GaN/AlN resonant tunneling diodes

This paper reports an enhancement of the nonvolatile memory characteristics of GaN/AlN resonant tunneling diodes (RTDs) by reducing the crystal defects in the quantum well structure. Pit-shaped crystal defects are strongly suppressed when pure N2, instead of a N2/H2 mixture, is used as a carrier gas and trimethylindium is introduced as a surfactant for metalorganic vapor phase epitaxy of the quantum well structure. In addition, the density of dislocations is lowered by controlling the growth conditions and structure of the buffer layer between a GaN/AlN RTD and a sapphire (0001) substrate. The leakage current through the quantum well structure is lowered, and an extremely high ON/OFF of >1300, which is 20 times higher than the values obtained in previous studies, is induced. Theoretical calculations based on Poisson’s equation and the Tsu–Esaki formula indicate that a high ON/OFF ratio of >103 can be enhanced by increasing the density of electrons accumulating in the quantum well to a level on the order of 1018 cm–3. Furthermore, nonvolatile memory operations were performed by inputting the sequential pulse voltages with a speed of nanosecond time scale which is faster than speeds of electron releases from the crystal defects. These results strongly indicate that the nonvolatile memory characteristics of GaN/AlN RTDs are due to intersubband transitions and electron accumulation in the quantum well and are not attributed to electron trapping by the crystal defects.