Resonant Tunneling Research Articles

DFT investigation of hydrogenated cove-edged boron nitride nanoribbons for resonant tunneling diodes application

The cove-defect is found to improve the stability of the nanoribbons through bond length reconstructions at the cove-edge. Density functional theory (DFT) and non-equilibrium Green’s function (NEGF)-based first principles calculations are used to examine the structural, electronic, and quantum transport aspects of the hydrogenated cove-edge defective zigzag boron nitride nanoribbons (ZBNNRs). The additional electronic states, originated by dangling bonds at the cove-edges, exist across the Fermi level making these structures purely metallic. Additionally, with high peak-to-valley current ratios (PVCR), the quantum transport properties’ negative differential resistance (NDR) features are obtained. The highest PVCR is calculated to be 3.60 × 1016. The presented cove-edge defects can have a lot of potential for ultra-scaled devices including resonant tunnel diodes (RTDs), memory, and nanoswitches, according to the NDR phenomenon discovered in cove-edge ZBNNRs.

A tunable sub-wavelength acoustic imaging planar metalens

Acoustic metamaterials can be used to fabricate metalenses that can achieve sub-wavelength imaging resolution, but the reported devices are often passive and cannot adapt to changes in working frequency. To this end, we propose a dynamic tunable acoustic imaging planar metalens by introducing a telescopic tube between two sets of perforated Fabry–Pérot resonant metamaterial lenses to adjust the combined length of the imaging hole. Since the working frequency of the Fabry–Pérot resonant structure is directly related to the thickness of the metalens, continuous adjustment of the working frequency can be achieved by continuously changing the length of the imaging hole. This Fabry–Pérot resonant perforated structure belongs to an acoustic metamaterial unit, which can be resonantly coupled with evanescent waves to enhance the evanescent waves carrying detailed information of objects, thereby realizing high-resolution imaging. Relying on the resonance tunneling effect of the imaging hole, high acoustic transmittance can be obtained at the working frequency, ensuring excellent imaging quality. Through numerical calculation and experimental measurement results, the imaging performance and tunability of the tunable sub-wavelength acoustic imaging metalens are demonstrated. The proposed tunable acoustic planar metalens overcomes the shortcomings of the fixed working frequency of passive metalenses and has potential applications in the fields of ultrasound imaging and medical diagnosis.

Defeating broken symmetry with doping: Symmetric resonant tunneling in noncentrosymetric heterostructures

Resonant tunneling transport in polar heterostructures is intimately connected to the polarization fields emerging from the geometric Berry-phase. In these structures, quantum confinement results not only in a discrete electronic spectrum, but also in built-in polarization charges exhibiting a broken inversion symmetry along the transport direction. Thus, electrons undergo highly asymmetric quantum interference effects with respect to the direction of current flow. By employing doping to counter the broken symmetry, we deterministically control the resonant transmission through GaN/AlN resonant tunneling diodes and experimentally demonstrate the recovery of symmetric resonant tunneling injection across the noncentrosymmetric double-barrier potential.

Tunable Quasistationary States in a One-dimensional Quantum Heterostructure

In this work, we focus on the quasistationary states, lifetime, and transmittance in opened quantum wells with biased and unbiased. In order to solve the quasibound states, the complex eigenenergies are solved in our calculation model by adaptive finite element method. We have demonstrated the accuracy to exam the numerical convergence. In this case, the 1D quantum heterostructure is commonly composed of GaAs and AlxGa1-xAs. With the different applied bias, the resonant tunneling and transmittance profiles could be changed, respectively. Increasing the thickness of the outermost barrier can be prevented an electron penetrated through the barrier from the quasistationary state. This is a useful way to design easily the high-speed switch for semiconductor devices. Our results of numerical calculations are good agreement with the argument principle method approach. These results are useful and helped us to design quantum devices and quantum computations.

Multi‐level wireless transmission using resonant tunneling diodes in 300‐GHz band

AbstractThe authors report on a terahertz band wireless communication experiment employing a resonant tunneling diode receiver (Rx) and uni‐travelling carrier photodiode transmitter. An intermediate‐frequency based transmission facilitates a low‐complexity envelope‐detection type Rx architecture for complex‐modulated signals. Forward error correction recoverable data‐rates using quadrature phase shift keying modulation and 16‐level quadrature amplitude modulation are 60 and 68 Gbit/s, respectively.

Characteristics of Resonant Tunneling in Nanostructures with Spacer Layers

The effect of spacer layers on electron transport through two-barrier nanostructures was studied using the numerical solution of the time-dependent Schrodinger–Poisson equations with exact discrete open boundary conditions. The formulation of the problem took into account both the active region consisting of a quantum well and barriers, as well as the presence of highly doped contact layers and spacer layers. The use of the time formulation of the problem avoids the divergence of the numerical solution, which is usually observed when solving a stationary system of the Schrodinger–Poisson equations at small sizes of spacer layers. It is shown that an increase in the thickness of the emitter spacer leads to a decrease in the peak current through the resonant tunneling nanostructures. This is due to the charge accumulation effects, which, in particular, lead to a change in the potential in an additional quantum well formed in the emitter spacer region when a constant electric field is applied. The valley current also decreases as the thickness of the emitter spacer increases. The peak current and valley current are weakly dependent on the thickness of the collector spacer. The collector spacer thickness has a strong effect on the applied peak and valley voltages. The above features are valid for all three different resonant tunneling nanostructures considered in this study. For the RTD structures based on Al0.3Ga0.7As/GaAs, the optimized peak current value Ipmax = 5.6 × 109 A/m2 and the corresponding applied voltage Vp = 0.44 V. For the RTD structures based on AlAs/In0.8Ga0.2As, Ipmax = 14.5 × 109 A/m2 (Vp = 0.54 V); for RTD structures based on AlAs/In0.53Ga0.47As, Ipmax = 45.5 × 109 A/m2 (Vp = 1.75 V).

Double-Heterostructure Resonant Tunneling Transistors of Surface-Functionalized Sb and Bi Monolayer Nanoribbons

Zigzag nanoribbons tailored from chemically surface-modified Sb or Bi monolayers by methyl, amino or hydroxyl are investigated through first-principles electronic-structure calculations to explore their potential applications in topological transport nanoelectronics. It is verified by Dirac-point-like energy dispersion of band-edges near Fermi level that the scattering-forbidden edge-states of these nanoribbons can give a topological conductive channel with extremely high electron mobility. Accordingly, Sb/SbXHn/Sb and Bi/BiXHn/Bi nanoribbon double-heterostructures (SbXHn or BiXHn: XHn = CH3, NH2, OH) are designed as resonant tunneling transistors and modeled by bipolar transport devices with their electron transport characteristics being calculated by nonequilibrium Green’s function combined first-principles schemes. Ballistic equilibrium conduction spectra and current-voltage characteristics prove that quantum conductance currents of these nanoribbon double heterostructures originate from the electron resonant tunneling between the topological edge-states of the two constituent Sb or Bi monolayer nanoribbons through the central barrier of SbXHn or BiXHn nanoribbon segment. This renders a high resonant current peak with strong negative differential conductance, thus being competent for zero-loss and ultrahigh-frequency resonant tunneling nanotransistors.

Electrothermal Monte Carlo Simulation of a GaAs Resonant Tunneling Diode

This paper deals with the electron transport and heat generation in a Resonant Tunneling Diode semiconductor device. A new electrothermal Monte Carlo method is introduced. The method couples a Monte Carlo solver of the Boltzmann–Wigner transport equation with a steady-state solution of the heat diffusion equation. This methodology provides an accurate microscopic description of the spatial distribution of self-heating and its effect on the detailed nonequilibrium carrier dynamics.

Analysis of terahertz double dielectric structure patch antenna using nitride semiconductors

AbstractRecently, gallium arsenide (GaAs)‐based resonant tunneling diode (RTD) oscillators and indium phosphorus (InP)‐based Schottky barrier diode (SBD) receivers have been studied in the terahertz (THz) band. The THz devices for practical use should operate at room temperature, be small in size, and have high output power. Therefore, this study was focused on gallium nitride (GaN), which possesses excellent material properties, such as wide bandgap characteristics and heteroepitaxy on Si substrates. The GaN‐based oscillators and receivers are expected to be compact, operate at room‐temperature, and act as a high‐power device for the THz‐band devices. However, GaN has crystal defects, which can cause instability in device operations. A double dielectric structure patch antenna composed of Silicon Nitride (SiN) and Benzo Cyclo Butene (BCB) with different dielectric constants was proposed to realize a GaN‐based THz transmitter and receiver. The antenna characteristics were investigated using the Finite Difference Time Domain (FDTD) method. The results showed that the SiN has little effect on the radiation, whereas the BCB is strongly responsible for the radiation. Comparing the absolute gain between the double dielectric structure and the conventional structure using the SiN, it was confirmed that the double dielectric structure can improve the absolute gain.

Probing flux and charge noise with macroscopic resonant tunneling

We report on measurements of flux and charge noise in an rf-SQUID flux qubit using macroscopic resonant tunneling (MRT). We measure rates of incoherent tunneling from the lowest energy state in the initial well to the ground and first excited states in the target well. The result of the measurement consists of two peaks. The first peak corresponds to tunneling to the ground state of the target well, and is dominated by flux noise. The second peak is due to tunneling to the excited state and is wider due to an intrawell relaxation process dominated by charge noise. We develop a theoretical model that allows us to extract information about flux and charge noise within one experimental setup. The model agrees very well with experimental data over a wide dynamic range and provides parameters that characterize charge and flux noise.

Tunneling-induced fractal transmission in valley Hall waveguides

The Valley Hall effect provides a popular route to engineer robust waveguides for bosonic excitations such a photons and phonons. The almost complete absence of backscattering in many experiments has its theoretical underpinning in a smooth-envelope approximation that neglects large momentum transfer and is accurate only for small bulk band gaps and/or smooth domain walls. For larger bulk band gaps and hard domain walls backscattering is expected to become significant. Here, we show that in this experimentally relevant regime, the reflection of a wave at a sharp corner becomes highly sensitive on the orientation of the outgoing waveguide relative to the underlying lattice. Enhanced backscattering can be understood as being triggered by resonant tunneling transitions in quasimomentum space. Tracking the resonant tunneling energies as a function of the waveguide orientation reveals a self-repeating fractal pattern that is also imprinted in the density of states and the backscattering rate at a sharp corner.

Tunable presynaptic weighting in optoelectronic spiking neurons built with laser-coupled resonant tunneling diodes

Optoelectronic artificial spiking neurons are regarded as promising core elements for novel photonic neuromorphic computing hardware. In this work, we investigate a modular optoelectronic spiking neuron built with an excitable resonant tunneling diode (RTD) coupled to a photodetector and a vertical-cavity surface-emitting laser (VCSEL). This work provides the first experimental demonstration of amplitude control of the fired optical spikes in the electrical-to-optical part of the artificial neuron, therefore introducing a simple way of weighting of the presynaptic spikes. This is achieved by tuning the VCSEL bias current, hence providing a straightforward, high-speed, hardware-friendly option for the weighting of optical spiking signals. Furthermore, we validate the feasibility of this layout using a simulation of a monolithically integrated, RTD-based nanoscale optoelectronic spiking neuron model, which confirms the system’s capability to deliver weighted optical spiking signals at GHz firing rates. These results demonstrate a high degree of flexibility of RTD-based artificial optoelectronic spiking neurons and highlight their potential towards compact, high-speed photonic spiking neural networks and light-enabled neuromorphic hardware.

In-Plane and Out-of-Plane Investigation of Resonant Tunneling Polaritons in Metal-Dielectric-Metal Cavities.

Polaritons can be generated by tuning the optical transitions of a light emitter to the resonances of a photonic cavity. We show that a dye-doped cavity generates resonant tunneling polaritons with Epsilon-Near-Zero (ENZ) effective permittivity. We studied the polariton spectral dispersion in dye-doped metal-dielectric-metal (MDM) cavities as a function of the in-plane (k||) and out-of-plane (k⊥) components of the incident wavevector. The dependence on k|| was investigated through ellipsometry, revealing the ENZ modes. The k⊥ dependence was measured by varying the cavity thickness under normal incidence using a Surface Force Apparatus (SFA). Both methods revealed a large Rabi splitting well exceeding 100 meV. The SFA-based investigation highlighted the collective nature of strong coupling by producing a splitting proportional to the square root of the involved photons. This study demonstrates the possibility of generating ENZ polaritons and introduces the SFA as a powerful tool for the characterization of strong light-matter interactions.

Planar AlN/GaN resonant tunneling diodes fabricated using nitrogen ion implantation

We report planar AlN/GaN resonant tunneling diodes (RTDs) fabricated using a nitrogen ion implantation isolation process on silicon substrates. The active area of AlN/GaN RTDs is defined by nitrogen ion implantation. A planar RTD consists of two different-sized RTDs connected in series, where the larger one acts as a resistor and the performance of the planar RTD is determined by the smaller one. Repeatable and hysteresis-free negative differential resistances without degradation are observed through 500 continuous bidirectional voltage sweeps. The peak current density is 15.5 kA/cm2. The RTD exhibits stable negative differential resistance (NDR), with the peak-to-valley current ratio varying from 1.39 to 1.28 as the temperature increases from 77 to 295 K. This practicable and reproducible ion implantation process is compatible with silicon fabrication technology. It, thus, provides a feasible method for device design of GaN-based RTDs and facilitates the implementation of complex monolithic microwave integrated circuits based on planar III-nitride RTDs on large-size silicon wafers.

On the relation between electrical and electro-optical properties of tunnelling injection quantum dot lasers

Abstract We present a comprehensive study of the temperature dependent electronic and optoelectronic properties of a tunnelling injection quantum dot laser. The optical power-voltage (P opt–V) characteristics are shown to be correlated with the current-voltage (I–V) and capacitance-voltage (C–V) dependencies at low and elevated temperatures. Cryogenic temperature measurements reveal a clear signature of resonant tunnelling manifested in periodic responses of the I–V and P opt–V characteristics, which diminish above 60 K. The C–V characteristics reveal a hysteresis stemming from charging and de-charging of the quantum dots, as well as negative capacitance. The latter is accompanied by a clear peak that appears at the voltage corresponding to carrier clamping, since the clamping induces a transient-like effect on the carrier density. C–V measurements lead also to a determination of the dot density which is found to be similar to that obtained from atomic force microscopy. C–V measurements enable also to extract the average number of trapped electrons in each quantum dot which is 0.95. As the important parameters of the laser have signatures in the electrical and electro-optical characteristics, the combination serves as a powerful tool to study intricate details of the laser operation.

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.

Tuning transport properties in carbyne-DNA fragments-carbyne devices

Here, we investigated the tuning transport properties from six nanodevices based on molecular tunnel junctions from DNA fragments and carbyne electrodes via DFT/NEGF. Our results show that for DNA fragments HOMOs and LUMOs locate at the purine (A and G) and pyrimidine (T and C) bases, respectively. This is an important factor to develop nanodevices. So, the influence of carbyne electrodes shows that molecular projected self-consistent hamiltonian (MPSH) states for HOMO (LUMO) locate DNA fragments (carbyne electrodes) presenting Zener diode and resonant tunnel diode (RTD) behavior as a current sensor for forward bias. A-G and T-C nanodevices operate at nA whereas A-G and T-C nucleoside or nucleotide at μA. Our discoveries make themhighly promising in nanoelectronics and nanobiosensors applications for tuning the transport properties.

Correlated topological pumping of interacting bosons assisted by Bloch oscillations

Thouless pumping, not only achieving quantized transport but also immune to moderate disorder, has attracted growing attention in both experiments and theories. Here, we explore how particle-particle interactions affect topological transport in a periodically modulated and tilted optical lattice. Three characterized interaction effects are revealed: topological pumping of bound states, interaction blockade of scattering states, and topologically resonant tunnelings. Attributed to the tilting, we have found a linear scanning in the first Brillouin zone at each Bloch-oscillation period of multiparticle center-of-mass momentum. Not limited to multiparticle Wannier states, our scheme ensures a dispersionless quantized transport even for initial Gaussian-like wave packets of interacting bosons which do not uniformly occupy a given band. Our study deepens the understanding of correlation effects on topological states, and provides a feasible way for detecting topological properties in interacting systems.

Spin thermoelectric effects of skyrmions in ferromagnetic topological insulators

The thermoelectric effects of ferromagnetic topological insulators with either two-dimensional circular or one-dimensional domain wall skyrmions are studied theoretically. It is found that the topological spin-textures play a significant role in the manipulation of spin-dependent thermoelectric properties. In the vicinity of the charge neutrality point, spin Seebeck coefficients possess finite values whose sign and magnitude can be tuned by temperature in spite of vanishing charge Seebeck coefficients. The majority of the effects of circular skyrmions occurs in the edge-state transport regime by generating Fano antiresonances. While the domain wall skyrmion primarily influences the thermoelectric behaviors near the boundary between the edge-state and bulk-state transport regimes with the resonant tunneling mechanism. Both types of skyrmions which function effectively in distinct transport regimes have potential applications in thermoelectrics.

Resonant tunneling of photons in layered optical nanostructures (metamaterials)

The conditions of resonant (almost complete) tunneling of photons (plane monochromatic electromagnetic waves) through layered dielectric and metal-dielectric structures are considered. Resonant tunneling occurs at frequencies at which the resonance conditions for the corresponding structures of open resonators are met. For metal-dielectric structures, the possibility of tunneling in the optical range with a strong barrier in the IR range is shown, which can be used to control the transmission of window panes. Keywords: dielectric permittivity, homogenization, resonant tunneling, plasmons, metal nanoparticles, window panes.