Resonant Tunneling Research Articles

Spin-Polarized Resonant Tunneling in Antiferromagnetic Heterojunctions of Graphene Nanoribbons with 3d Adatoms

Binding, magnetic, and electron transport properties of $3d$ transition-metal (TM) adatoms ($\mathrm{Cr}$-$\mathrm{Cu}$) on an antiferromagnetic armchair graphene nanoribbon heterojunction are studied by means of density-functional-theory (DFT) calculations and nonequilibrium Green function (NEGF) formalism. The heterojunction emulates a system of two symmetric potential barriers and one well with resonances (quasibound states). Binding energies show a strong interaction between $3d$ TM adatoms and heterojunction hollow sites, where $3d$ TM adatoms prefer the edges rather than the middle of the graphene heterojunction. As for magnetic properties, heterojunctions with Cr, $\mathrm{Mn}$, and $\mathrm{Fe}$ have a ferromagnetic behavior with a total magnetic moment $\ensuremath{\ge}4{\ensuremath{\mu}}_{B}$, while $\mathrm{Co}$, $\mathrm{Ni}$, and $\mathrm{Cu}$ adatoms induce antiferromagnetism in the full system with total magnetizations $<3{\ensuremath{\mu}}_{B}$. Transmission curves show that electronic resonances undergo a spin-splitting effect induced by $3d$ TM adatoms, and current versus bias-voltage curves show spin currents from which spin-polarized ratios (SPRs) $>75\mathrm{%}$ for $\mathrm{Co}$ and approximately $100\mathrm{%}$ for $\mathrm{Ni}$ adatoms are calculated. Finally, an oscillatory behavior is observed in SPR curves at low bias due to a combined effect of resonant tunneling and spin filtering. Therefore, these results suggest that the present antiferromagnetic graphene heterojunction with $\mathrm{Co}$ and $\mathrm{Ni}$ adatoms is suitable for future spin and low-power nanoelectronics as a spin-dependent resonant tunneling device.

Robust valley filter induced by quantum constructive interference in graphene with line defect and strain

In this paper, we theoretically investigate the manipulation of valley-polarized currents and the optical-like behaviours of Dirac fermions in graphene with single line defect. After the introduction of a local uniaxial strain, the valley transmission probability increases and transmission plateau emerges in a large angle range. Such phenomenon originates from resonant tunnelling, and the strain act as an antireflective coating for the valley states, analogous to the antireflective coating in an optical device. This indicates that perfect valley polarization can occur in a larger incident angle range compared with solely line defect. Interestingly, in the presence of Anderson disorder, even though the transmission decreases, the valley polarization is still robust. Our theoretical findings may be experimentally observable and valuable for valleytronic applications based on graphene.

Resonant tunneling light emitting diode based on rock-salt ZnO/MgO multiple quantum well

The rock-salt structure ZnO is favorable for optoelectronic applications due to its high symmetry and a promising rock-salt. However, this high-pressure phase is metastable under ambient conditions. This work presents experimental results for rock-salt ZnO/MgO multiple quantum well (RS-MQW) and its resonant tunneling light emitting diode (RTLED). Near ultraviolet and blue-violet electroluminescence centered at 396 nm is observed from the RTLED. The electroluminescence is naked eye visible even at a forward injection current as low as 0.5 mA. The absolute radiation fluxes in the spectral range of 365 nm–465 nm and 390 nm–400 nm reach to 246.6 μW and 57.0 μW, respectively, at 10 mA injection current. The luminance of the RTLED is 10643 cd/m2. This work shows an application of rock-salt ZnO in light emitting diodes.

Artificial optoelectronic spiking neuron based on a resonant tunnelling diode coupled to a vertical cavity surface emitting laser.

Excitable optoelectronic devices represent one of the key building blocks for implementation of artificial spiking neurons in neuromorphic (brain-inspired) photonic systems. This work introduces and experimentally investigates an opto-electro-optical (O/E/O) artificial neuron built with a resonant tunnelling diode (RTD) coupled to a photodetector as a receiver and a vertical cavity surface emitting laser as a transmitter. We demonstrate a well-defined excitability threshold, above which the neuron produces optical spiking responses with characteristic neural-like refractory period. We utilise its fan-in capability to perform in-device coincidence detection (logical AND) and exclusive logical OR (XOR) tasks. These results provide first experimental validation of deterministic triggering and tasks in an RTD-based spiking optoelectronic neuron with both input and output optical (I/O) terminals. Furthermore, we also investigate in simulation the prospects of the proposed system for nanophotonic implementation in a monolithic design combining a nanoscale RTD element and a nanolaser; therefore demonstrating the potential of integrated RTD-based excitable nodes for low footprint, high-speed optoelectronic spiking neurons in future neuromorphic photonic hardware.

Repeatable room temperature negative differential resistance in AlN/GaN resonant tunneling diodes grown on silicon

We report repeatable AlN/GaN resonant tunneling diodes (RTDs) grown on a silicon substrate by plasma-assisted molecular-beam epitaxy. The RTDs exhibit stable negative differential resistance without hysteresis at room temperature, where no degradation is observed even after 500 continuous bidirectional sweeps. The peak-to-valley current ratio is 1.36, and the peak current density is 24.38 kA/cm2. When the temperature is changed from 77 to 475 K, the peak current remains almost unchanged and the valley current increases gradually, resulting in a reduced peak-to-valley current ratio from 1.59 to 1.07. Our work softens the material quality constraints on realizing the room-temperature repeatable negative differential resistance and paves the way to low-cost III-nitride-based monolithic and hybrid microwave integrated circuits on large-size silicon wafers.

Carrier Dynamics for the Collective Resonant Tunneling in Quantum Dot-Based Artificial Graphene

Carrier Dynamics for the Collective Resonant Tunneling in Quantum Dot-Based Artificial Graphene

Cross-Coupled Gated Tunneling Diodes With Unprecedented PVCRs Enabling Compact SRAM Design—Part I: Device Concept

Tunnel diodes (TDs) and resonant tunneling diodes (RTDs) with negative differential resistance (NDR) have attracted interest in implementing high-density, low-power circuits, such as static random access memory (SRAM). However, the low peak-to-valley current ratios (PVCRs) in these devices cause high static leakage currents, leading to poor performance in the circuits and limiting their application. This article presents a novel device, i.e., a cross-coupled gated tunneling diode (XTD), that exhibits NDR with PVCRs exceeding <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10^{{5}}$ </tex-math></inline-formula> . The device design is validated by TCAD simulation as well as an experimental demonstration. In contrast to conventional TDs, which operate in the forward bias direction, the XTD operates in the reverse bias direction, thus suppressing thermionic emission and trap-assisted tunneling (TAT) currents, which together allow for the large PVCR. In Part II of this article, we continue to discuss compact, low-power SRAM cells based on the XTD.

The hydrogen bond rotation of confined water affected by quantum resonance tunnelling

In this work, we report quantum tunnelling effects on the confined water chain flipping, different from the spatial size and even electronic correlation effects of the confinement environment. First-principles calculations and analyses confirm that quantum tunnelling from the water chain itself enhances the hydrogen bond rotation. Importantly, the neglected resonant tunnelling can result in tunnelling rotation of hydrogen bonds with a probability close to 1 through the provided 0.6 eV energy, while the probability of generally recognized sequential tunnelling is only 10−6. Not only that, compared to sequential tunnelling, resonant tunnelling leads to a 20 K higher flipping temperature of the water chain. Additionally, the ratio of the resonant tunnelling probability to the thermal disturbance probability at 200 K is at least ten times larger than that of sequential tunnelling, which further illustrates the enhancement of hydrogen bond rotation brought about by resonant tunnelling.

Resonant tunneling in graphene-ferroelectric-graphene junctions

We study tunnel junctions consisting of a two-dimensional ferroelectric (FE) material sandwiched between graphene electrodes. We formulate a theory for the interplay of the FE polarization and induced free charges in such devices, taking into account quantum capacitance effects. We predict a gate-sensitive FE voltage difference across the device, which can be measured using electrostatic force microscopy. Incorporating this electrostatic theory in the tunneling current-voltage characteristics, we identify a resonance peak associated with aligned Dirac cones as a highly sensitive probe of the FE polarization of the junction. This opens the way for device applications with few atom-thick FE layers acting as readable ultra-high-density memory.

Goos–Hänchen shift of a light beam tunable by graphene in the resonant optical tunneling structure

The structure for implementing resonant optical tunneling effect is a simple layered system of dielectrics that provides full light transmission for resonance condition, despite the presence of barrier layers partially locking light. The presence of a sharp resonant peak both for the intensity and for the spatial shift of the transmitted light beam makes such a structure promising for the creation of sensors and light control devices. This paper focuses on the spatial shift called the Goos–Hänchen shift of such a structure with interfaces of the waveguide layer coated by graphene. The effect of Goos–Hänchen shift near the resonance in this case may be controlled by small changes in the chemical potential or the Fermi energy of graphene, which can be controlled both chemically and by electrical bias. The characteristics of transmitted light beam strongly depend on the beam width for the selected optimal focusing condition.

Magnetic Fingerprints in an All-Organic Radical Molecular Break Junction.

Polycyclic aromatic hydrocarbons radicals are organic molecules with a nonzero total magnetic moment. Here, we report on charge-transport experiments with bianthracene-based radicals using a mechanically controlled break junction technique at low temperatures (6 K). The conductance spectra demonstrate that the magnetism of the diradical is preserved in solid-state devices and that it manifests itself either in the form of a Kondo resonance or inelastic electron tunneling spectroscopy signature caused by spin-flip processes. The magnetic fingerprints depend on the exact configuration of the molecule in the junction; this picture is supported by reference measurements on a radical molecule with the same backbone but with one free spin, in which only Kondo anomalies are observed. The results show that the open-shell structures based on the bianthracene core are interesting systems to study spin–spin interactions in solid-state devices, and this may open the way to control them either electrically or by mechanical strain.

Vibration‐Assisted Charge Transport through Positively Charged Dimer Junctions

AbstractIntermolecular charge transport plays a vital role in the fields of electronics, as well as biochemical systems. Here, we design supramolecular dimer junctions and investigate the effects of charge state and energy level alignment on charge transport under nanoconfinement. Incoherent tunneling caused by thermally‐induced vibrations is enhanced in positively charged systems. The transition between coherent and incoherent tunneling is associated with specific molecular vibration modes. Positively charged systems with smaller torsional barriers and vibrational frequencies result in lower transition temperatures. Multiple thermal effects have a great impact on the conductance in the off‐resonant tunneling, while thermally‐induced vibron‐assisted tunneling contributes more to the transport in the resonant tunneling. These investigations offer a deep mechanism understanding of intermolecular charge transport and facilitate the development of practical functional molecular devices.

Vibration-Assisted Charge Transport through Positively Charged Dimer Junctions.

Intermolecular charge transport plays a vital role in the fields of electronics, as well as biochemical systems. Here, we design supramolecular dimer junctions and investigate the effects of charge state and energy level alignment on charge transport under nanoconfinement. Incoherent tunneling caused by thermally-induced vibrations is enhanced in positively charged systems. The transition between coherent and incoherent tunneling is associated with specific molecular vibration modes. Positively charged systems with smaller torsional barriers and vibrational frequencies result in lower transition temperatures. Multiple thermal effects have a great impact on the conductance in the off-resonant tunneling, while thermally-induced vibron-assisted tunneling contributes more to the transport in the resonant tunneling. These investigations offer a deep mechanism understanding of intermolecular charge transport and facilitate the development of practical functional molecular devices.

Broadband directional resonant tunneling emission enhancement via acoustic anisotropic metamaterials

Broadband directional acoustic emission enhancement is essential in practical applications, such as acoustic communication and medical imaging. In this paper, an anisotropic metamaterial array of meta-unit consisting of a straight channel and four symmetrical side branch cavities is proposed, aiming to achieve broadband directional resonant tunneling acoustic emission enhancement via the coupling of the transmission peaks in the y-direction. In the range of 3335–4625 Hz, the broadband anisotropic characteristic is reflected in the opposite transmission capacities of the meta-unit and periodic array in the orthogonal directions, which is caused by the different effective impedances due to resonant tunneling. Numerical simulation shows that for the anisotropic metamaterial array with a monopole source in the center, the broadband directional acoustic emission enhancement phenomenon appears in the y-direction. The experimental results confirm that at a distance of 35 cm from the point source, the SPL gain in the y-direction is 4 dB on average, and the SPL in the x-direction is reduced by an average of 12 dB. Based on the above results, the proposed anisotropic metamaterial array is expected to show significant potential applications in the fields where broadband acoustic signals are required.

Coherent brightening of a multilayer MQW− structure taking into account resonant tunneling for ultra-short IR pulses in a transverse electric field

The features of the effect of self-induced transparency (SIT) in a multi-well M Q W − structure with two working levels in quantum wells (QWs) in a transverse electric field are considered. The cycle of energy exchange between an ultrashort pulse and the resonant medium of two-level systems, which leads to coherent bleaching of the M Q W − structure, is complicated by resonant tunneling between the size-quantization levels of neighboring QWs. The behavior of a radiation pulse during the propagation of two-level QWs in a resonant medium in the self-transparency regime is analyzed. Analytical dependences of various branches of evolution and possible transition conditions between branches for propagating pulses are demonstrated. Practical possibilities are pointed out for deforming the envelope profile and the duration of the radiation pulse by varying the strength of the applied external electric field. The direct possibility for such controlled manifestations of the SIT effect as propagation without absorption, pulse delay, and variation of the observability threshold is emphasized. • The features of the self-induced transparency (SIT) effect in a multi-well MQW-structure with two working levels in quantum wells (QWs) are considered. • The structure is placed in a transverse electric field directed perpendicularly to the vertical walls of the QW, which ensures that the ground level of one well coincides with the energy of the excited level of the neighboring well. • The cycle of energy exchange between an ultra-short pulse and the resonant medium of two-level system is complicated by the processes of resonant tunneling between the quantum-confinement levels of neighboring QWs. • The behavior of a radiation pulse during propagation of two-level QWs in a resonant medium is analyzed taking into account resonant tunneling between neighboring QWs in the self-transparency mode.

Admittance Spectroscopy Up to 67 GHz in InGaAs/InAlAs Triple-Barrier Resonant Tunneling Diodes

Admittance Spectroscopy Up to 67 GHz in InGaAs/InAlAs Triple-Barrier Resonant Tunneling Diodes

The resonant condition of transmission in the graphene-based double-barrier structures

The Klein tunneling of Dirac fermions through a symmetric double potential barrier of a rectangular shape in graphene has been investigated. A new analytical formula for a dependence of the transmission coefficient of electrons on the angle of incidence on the barrier was obtained, on the basis of which the conditions for the angles of incidence with 100% transmission were found. In the case of a double potential barrier we have three conditions for resonance tunneling, two of which are similar to those conditions for one barrier, and the third one reflects the presence of the second barrier.

Quasi-linear and Plateaus-like Tunneling Magnetoresistance in Graphene-based Tunable Magnetic Barrier Nanostructures

The effect of electrostatic and magnetic vector potentials pattern on electrical properties and the tunneling magnetoresistance in graphene junction with periodic magnetic vector potentials are theoretically investigated using the transfer matrix method. The magnetic structure on graphene can control the direction of the magnetizations which correspond to the parallel and anti-parallel (AP) configurations. In AP magnetic structures with the applied gate voltage pattern, USUBA/SUB (U₁ = U₂), the shift of the conductance-peak position as a function of Fermi energy. The peak corresponds to resonant tunneling, where the incidence energy of the tunneling electron equals the confinement energy, and the conductance peak decrease approximately linearly with increasing electrostatic potential. The peak position occurs at ESUBF/SUB = 0.5U where it is shifted to higher Fermi energy with higher gate potential, but for the case of USUBB/SUB (U₁ = -U₂), the peak height is reduced rapidly, and the width increase as gate potential increases. Because of the periodic magnetic field with zero spatial average in the antiparallel structure, we found that the minimum conductivity decreases with increasing magnetic energy. They show suppression of Klein tunneling which occurs in the zero-conductance plateaus and leads to the robust magnetoresistance plateau and large positive magnetoresistance appears below magnetic energy. For the case of USUBA/SUB and ESUBF/SUB more than magnetic energy, we found that the quasi-linear magnetoresistance feature is applied by an electric field instead of the usual magnetically driven magnetoresistance.

Surface passivation in c-Si solar cells via a double-barrier quantum-well structure for ameliorated performance

Modern solar cell technology suffers low surface passivation, high recombination losses at the interface, and dopant diffusion losses that limit solar cell’s efficiency. Therefore, a double-barrier quantum-well (DBQW) structure-based surface passivation contact is introduced here to resolve these shortcomings. In this regard, DBQWs of different thicknesses with stacks of SiOx/ nc-SiOx (3, 5, 8, and 10 nm)/SiOx layers were explored as surface passivation layers and dopant diffusion barriers. Multiple characterizations were utilized to examine DBQW thickness-dependent properties, such as contact resistance, passivation, and recombination current density; the best result was for the 5-nm-thickness QW passivation layer. To justify the obtained result, theoretical calculations were carried out based on the experimental results, which suggested the resonance tunneling of charge carriers across the 5 nm DBQW structure. Furthermore, SIMS was explored to examine the diffusion barrier property of these QWs, which revealed that dopant diffusion was suppressed by the QW with the double SiOx layer. Finally, the nc-SiOx(n) /5-nm QW/c-Si surface passivation structure showed substantial enhancement in a lifetime (τeff) of 3560 μs, an implied open-circuit voltage (iVoc) of 735 mV, and reduced recombination current density (Jo) = 1.5 fA/cm2.

Band bending induced resonant tunneling in ferroelectric tunnel junctions

Aside from direct tunneling, resonant tunneling could be introduced into ferroelectric tunnel junctions (FTJs) to improve the functionalities. Using a quantum-mechanical model of tunneling, we studied the band bending induced resonant tunneling in FTJs where the band bending could be realized by a proper composite layer and an interface dipole layer. We hope that our work could stimulate further studies of resonant tunneling effects in FTJs.