Resonant Tunneling Behavior Research Articles

A Room-Temperature Ferroelectric Resonant Tunneling Diode.

Resonant tunneling is a quantum-mechanical effect in which electron transport is controlled by the discrete energy levels within a quantum-well (QW) structure. A ferroelectric resonant tunneling diode (RTD) exploits the switchable electric polarization state of the QW barrier to tune the device resistance. Here, the discovery of robust room-temperature ferroelectric-modulated resonant tunneling and negative differential resistance (NDR) behaviors in all-perovskite-oxide BaTiO3 /SrRuO3 /BaTiO3 QW structures is reported. The resonant current amplitude and voltage are tunable by the switchable polarization of the BaTiO3 ferroelectric with the NDR ratio modulated by ≈3 orders of magnitude and an OFF/ON resistance ratio exceeding a factor of 2×104 . The observed NDR effect is explained an energy bandgap between Ru-t2g and Ru-eg orbitals driven by electron-electron correlations, as follows from density functional theory calculations. This study paves the way for ferroelectric-based quantum-tunneling devices in future oxide electronics.

Subband-resolved momentum-conserved resonant tunneling in monolayer graphene/h-BN/ABA-trilayer graphene small-twist-angle tunneling device

We demonstrate twist-controlled resonant tunneling in a monolayer graphene (MLG)/hexagonal boron nitride (h-BN)/ABA-stacked trilayer graphene (TLG) van der Waals (vdW) junction, in which MLG and TLG flakes are aligned with a small twist angle θ of ∼1.05° between their crystallographic orientations through a thin h-BN barrier. Owing to the small interlayer twist, resonant tunneling attributed to the conservation of momentum and energy was observed between the single linear band of MLG and multiple subbands of TLG. We show that different subbands of TLG—bilayer-graphene-like subbands and a MLG-like subband—exhibit distinctly different resonant tunneling behaviors. Therefore, we demonstrate subband-resolved resonant tunneling. This technique provides a method to determine band parameters (Slonczewski–Weiss–McClure parameters) and probes the band dispersion of different two-dimensional materials by utilizing a MLG electrode.

Van der Waals Doping and Room Temperature Resonant Tunneling Observed in Black Phosphorus/Germanium Sulfide Transistors

Abstractvan der Waals semiconductors have proven to be exceptional for electronic and photonic applications. Although most research is extensively focused on some transition metal dichalcogenides materials (MX2) such as MoS2, WS2, WSe2, and MoSe2, studies on 2D metal monochalcogenides such as germanium sulfide (GeS) has been widely under investigated, mainly due to the high contact resistance GeS devices exhibit. Here, a van der Waals field‐effect transistor (VdW‐FET) based on GeS is investigated and resonant tunneling behavior is shown at room temperature due to VdW doping via black phosphorus (BP), evident by the observation of multiple decades of negative differential resistance (NDR) during doping transient state. These NDR decades are caused by confinement of carriers inside the double barrier quantum well, which allows tunneling to occur for discrete energy levels. Moreover, a noticeable conductivity switch from a low p‐type to a high n‐type is observed, with a conductivity enhancement of 2 orders of magnitude compared to pristine GeS devices. The underlying mechanism behind the observed NDR and the conductivity switch is discussed and it is shown that these phenomena are likely caused by phosphorus doping due to BP sublimation, evident by the detected P‐Ge Raman peak in the measured Raman spectra. The results can open doors for electrical oscillators and switching devices for the next generation of nanoelectronics.

Direct fabrication and characterization of vertically stacked Graphene/h-BN/Graphene tunnel junctions

We have used a lithography free technique for the direct fabrication of vertically stacked two-dimensional (2D) material-based tunnel junctions and characterized by Raman, AFM, XPS. We fabricated Graphene/h-BN/Graphene devices by direct deposition of graphene (bottom layer), h-BN (insulating barrier) and graphene (top layer) sequentially using a plasma enhanced chemical vapor deposition on Si/SiO2 substrates. The thickness of the h-BN insulating layer was varied by tuning the plasma power and the deposition time. Samples were characterized by Raman, AFM, and XPS. The I-V data follows the barrier thickness dependent quantum tunneling behavior for equally doped graphene layers. The resonant tunneling behavior was observed at room temperature for oppositely doped graphene layers where hydrazine and ammonia were used for n-doping of one of the graphene layers. The resonance with negative differential conductance occurs when the band structures of the two electrodes are aligned. The doping effect of the resonant peak is observed for varying doping levels. The results are explained according to the Bardeen tunneling model.

Resonant tunneling and hole transport behavior in low noise silicon tri-gate junctionless single hole transistor

The fabrication of p-type silicon junctionless tri-gate transistors and their temperature dependent transport studies are reported in this work. The fabricated transistors have shown a good transfer characteristic down to a low temperature of ∼ 80 K with an ON/OFF ratio of 106. The threshold voltage and the subthreshold slope were found to be dependent on temperature. In particular, the threshold voltage and the flat band voltage have positive slopes of 2.24 and 1.19 mV K−1, respectively, with temperature. Channel resistance was found to be increasing with decreasing temperature. The devices have shown a typical 1/f noise behavior in the frequency range of (1–50) Hz and 1/f2 type behavior in the frequency range of (50–100 Hz). At a temperature of 4.2 K, current vs. gate voltage characteristic at a fixed source drain bias shows clear coulomb peaks with different intervals for different gate bias voltages and the observed spikes were consistent within the sub-bands. We relate this to the single hole tunneling, mediated by the charged acceptors available in the channel region. Coupling strength of the dopants was also studied.

Resonant transport in Kekulé-distorted graphene nanoribbons

The formation of a superlattice in graphene can serve as a way to modify its electronic band structure and thus to engineer its electronic transport properties. Recent experiments have discovered a Kekulé bond ordering in graphene deposited on top of a copper substrate, leading to the breaking of the valley degeneracy while preserving the highly desirable feature of linearity and gapless character of its band dispersion. In this paper, we study the effects of a Kekulé distortion in zigzag graphene nanoribbons in both the subband spectrum and on its electronic transport properties. We extend our study to also investigate the electronic conductance in graphene nanoribbons composed of sequentially ordered ν=±1 Kek-Y superlattices. We find interesting resonances in the conductance response emerging in the otherwise energy gap regions, which scales with the number of Kek-Y interfaces minus one. Such features resemble the physics of resonant tunneling behavior observed in semiconductor heterostructures. Our findings provide a possible way to measure the strength of the Kekulé parameter in graphene nanoribbons.

Charge transport in doped zigzag phosphorene nanoribbons

The effects of lattice distortion and chemical disorder on charge transport properties of two-terminal zigzag phosphorene nanoribbons (zPNRs), which shows resonant tunneling behavior under an electrical applied bias, are studied. Our comprehensive study is based on ab initio quantum transport calculations on the basis of the Landauer theory. We use nitrogen and silicon substitutional dopant atoms, and employ different physical quantities such as the $I\text{\ensuremath{-}}V$ curve, voltage drop behavior, transmission spectrum, transmission pathway, and atomic current to explore the transport mechanism of zPNR devices under a bias voltage. The calculated transmission pathways show the transition from a ballistic transport regime to a diffusive and in some particular cases to localized transport regimes. Current flowing via the chemical bonds and hopping are monitored; however, the conductance originates mainly from the charge traveling through the chemical bonds in the vicinity of the zigzag edges. Our results show that in the doped systems, the device conductance decreases and the negative differential resistance characteristic becomes weak or is eliminated. Besides, the conductance in a pure zPNR system is almost independent of the ribbon width.

Theoretical analysis of 1D resonant tunneling behavior in ion-enhanced cold field and thermo-field emission

In cold field and thermo-field emission, positive ions or adsorbates very close to the cathode surface can enhance emission current by both resonant and non-resonant processes. In this paper, resonant tunneling behavior is investigated by solving the one-dimensional Schrödinger equation in the presence of an ion, and the enhancement due to resonant processes is evaluated. Results shows that as the applied electric field increases, the resonant states move from higher to lower energies as the ion energy levels are shifted down. Conversely, as the ion position moves closer to the cathode, the resonant states shift up in energy. Further, through a simplified perturbation analysis, the general scaling of these trends can be predicted. These shifts of resonant states directly impact the emission current density, and they are especially relevant when the applied field is on the order of a few volts per nanometer (∼0.5–3 V/nm) and the ion is a few nanometers (∼0.5–3 nm) away from the cathode. Further, when the energy level for resonant emission coincides with the Fermi level of a metallic cathode, the current density is particularly enhanced. The results of this study suggest that it may be possible to control (augment/inhibit) the resonant emission current by manipulating the supply function of a cathode relative to the operating conditions of the emitter in either ion-enhanced or adsorbate-enhanced field emission, which can be applied to various plasma and electron emission technologies.

Resonant tunnelling in a quantum oxide superlattice.

Resonant tunnelling is a quantum mechanical process that has long been attracting both scientific and technological attention owing to its intriguing underlying physics and unique applications for high-speed electronics. The materials system exhibiting resonant tunnelling, however, has been largely limited to the conventional semiconductors, partially due to their excellent crystalline quality. Here we show that a deliberately designed transition metal oxide superlattice exhibits a resonant tunnelling behaviour with a clear negative differential resistance. The tunnelling occurred through an atomically thin, lanthanum δ-doped SrTiO3 layer, and the negative differential resistance was realized on top of the bipolar resistance switching typically observed for perovskite oxide junctions. This combined process resulted in an extremely large resistance ratio (∼10(5)) between the high and low-resistance states. The unprecedentedly large control found in atomically thin δ-doped oxide superlattices can open a door to novel oxide-based high-frequency logic devices.

Performance analysis of a tunneling thermoelectric heat engine with nano-scaled quantum well

A numerical model of a nano-scaled thermoelectric heat engine with InP/InAs/InP trilayer quantum well (QW) is investigated. The expressions of those performance parameters, such as current, power output, and efficiency are expressed. By numerical calculation, the resonant tunneling behavior of electrons in the QW is described, which seems like a very good energy selective electron mechanism for the heat engine. After considering the radiation heat leakage, for fixed layer thicknesses of the QW, the optimum working regions of the heat engine with respect to the chemical potentials and the bias voltage are obtained numerically under the economic criterion. From these results, the power output can be increased by narrowing down the layer thicknesses. In addition, owing to the radiant heat leakage, the efficiency initially increases in the working regions and then decreases when the layer thicknesses increase gradually, from which one can obtain a maximum efficiency by optimizing layer thicknesses of QW. These results calculated here may provide a guide for the optimum designs of tunneling thermoelectric devices.

Resonant tunneling through double-barrier structures on graphene

Quantum resonant tunneling behaviors of double-barrier structures on graphene are investigated under the tight-binding approximation. The Klein tunneling and resonant tunneling are demonstrated for the quasiparticles with energy close to the Dirac points. The Klein tunneling vanishes by increasing the height of the potential barriers to more than 300 meV. The Dirac transport properties continuously change to the Schrödinger ones. It is found that the peaks of resonant tunneling approximate to the eigen-levels of graphene nanoribbons under appropriate boundary conditions. A comparison between the zigzag- and armchair-edge barriers is given.

Spin-dependent resonant tunneling of multiferroic tunnel junction via head-to-head 180° domain wall

The extraordinary properties of the two-dimensional electron gas (2DEG) at oxide heterostructure interface such as LaAlO3/SrTiO3 have attracted considerable investigations. Recent work suggested that the 2DEG could be formed within the SrTiO3 tunnel barrier by replacing the central TiO2 atomic layer with LaO, and that such a tunnel junction exhibits resonant tunneling behavior with new intriguing properties and potential applications [J. D. Burton et al., Phys. Rev. B 80, 115408 (2009)]. Here we investigate an alternative approach providing the resonant transmission of which a 180° head-to-head (HH) domain wall in the middle of the tunnel barrier induces the 2DEG via the free electronic carriers screening the polarization bound charges in situ. Using first-principles calculations on the Fe/PbTiO3/Fe as a model system, we show that this strategy allows for the formation of a 2DEG within the barrier, and that the remarkable difference between the majority- and minority-spin channels results in large tunneling magnetoresistance (TMR) effect. The resonant tunneling and the large TMR effect are beneficial to magnetic recording applications. We also discuss the feasibility to obtain such a 180° HH domain wall in the practical magnetic tunnel junctions and the influences of FeO formation at the iron-complex oxide interface on the electronic structure and tunneling properties.

Transport properties of two finite armchair graphene nanoribbons

In this work, we present a theoretical study of the transport properties of two finite and parallel armchair graphene nanoribbons connected to two semi-infinite leads of the same material. Using a single Π-band tight binding Hamiltonian and based on Green’s function formalisms within a real space renormalization techniques, we have calculated the density of states and the conductance of these systems considering the effects of the geometric confinement and the presence of a uniform magnetic field applied perpendicularly to the heterostructure. Our results exhibit a resonant tunneling behaviour and periodic modulations of the transport properties as a function of the geometry of the considered conductors and as a function of the magnetic flux that crosses the heterostructure. We have observed Aharonov-Bohm type of interference representing by periodic metal-semiconductor transitions in the DOS and conductance curves of the nanostructures.

Enhanced spin contrast of epitaxial Mn films on Fe(100) by spin-polarized scanning tunneling microscopy

The magnetic ordering in ultrathin Mn films grown on Fe(100) substrates is studied using spin-polarized scanning tunneling microscopy/scanning tunneling spectroscopy. Enhancement of spin contrast is observed due to a tip modification. Detailed analysis carried out using normalized dI/dV spectra indicates the appearance of resonant tunneling behavior. This is attributed to the attachment of a magnetic cluster at the apex of the magnetic thin film tip. Our results compare well with a recent theoretical prediction of a high vacuum spin-polarization of an Fe tip with an antiferromagnetically coupled Mn adatom [Ferriani et al., Phys. Rev. B 82, 054411 (2010)].

Coherent transport of armchair graphene constrictions

The coherent transport properties of armchair graphene nanoconstrictions (GNC) are studied using tight-binding approach and Green’s function method. We find a nonbonding state at zero Fermi energy which results in a zero conductance valley, when a single vacancy locates at y=3n±1 of a perfect metallic armchair graphene nanoribbon (aGNR). However, the nonbonding state does not exist when a vacancy locates at y=3n, and the conductance behavior of lowest conducting channel will not be affected by the vacancy. For the square-shaped armchair GNC consisting of three metallic aGNR segments, resonant tunneling behavior is observed in the single channel energy region. We find that the presence of localized edge state locating at the zigzag boundary can affect the resonant tunneling severely. A simplified one dimensional model is put forward at last, which explains the resonant tunneling behavior of armchair GNC very well.

Energy selective contacts for hot carrier solar cells

Double barrier resonant tunnelling structures consisting of silicon quantum dots (QDs) in silicon dioxide ( SiO 2 ) matrix have been studied for Energy Selective Contacts for Hot Carrier solar cell. A single layer of silicon QDs has been fabricated by high temperature annealing of SiO 2 / Si-rich oxide (SRO)/ SiO 2 layers deposited by RF magnetron sputtering. Compositional analysis of SRO films obtained with different sputtering target has been accurately measured with Rutherford backscattering spectroscopy. Size-controlled growth of Si QDs has been studied with photoluminescence measurements which demonstrate that QD sizes can be controlled with SRO layer thickness. In addition, resonant tunnelling behaviour of SiO 2 / Si QD/ SiO 2 structures has been investigated.

Hybrid Nanoparticle/Organic Devices with Strong Resonant Tunneling Behaviors

AbstractA hybrid nanoparticle/organic device consisting of small molecule organic semiconductors and Ag nanoparticles is reported. The single device exhibits unusual properties of organic resonant tunneling diode (ORTD) at low driving voltage region and offers light emission at high voltage. For ORTD, a strong negative differential resistance behavior is demonstrated at room temperature. The current resonance with the peak‐to‐valley current ratio of over 4.6 and narrow linewidth of only ∼1.4 V is achieved. A detailed operating mechanism of the charging and emission modes is proposed, which can be discussed in terms of the strong charge‐trapping effect of Ag nanoparticles. The repeatable operations of hybrid device show the mutual influences between two modes and the light emission properties of the ORTD are also discussed.

Nanoparticle-induced resonant tunneling behaviors in small molecule organic light-emitting devices

We report a hybrid nanoparticle/organic device with strong resonant tunneling behavior by introducing ligand-capped Ag nanoparticles between indium tin oxide and hole transport layer in small molecule organic light-emitting devices. The dependences of resonant tunneling current on the thickness of the organic layers are investigated. For the optimized device, a peak-to-valley current ratio as high as 4.5 and narrow peak width about 1.8 V are obtained. Combining with the analysis of current-voltage behavior, the mechanism based on the charge trapping effect of Ag nanoparticles is proposed to interpret the operation of the hybrid device. Finally, the emission characteristics of hybrid devices are also studied.

The size effects of electrodes in molecular devices: an ab initio study on the transport properties ofC60

The role of electrodes in the transport properties of molecular devices is investigated by takingC60 as an example and using gold nanowire and a gold atomic chain as theelectrodes. The calculations are done by an ab initio method combined with thenon-equilibrium Green function technique. We find that devices in which a singleC60 molecule is connected with different electrodes show completely different transport behavior. In the caseof nanowire/C60/nanowire the device shows a metallic behavior with a big equilibrium conductance (about2.18G0) and the current increases rapidly and almost linearly starting from zero. The transmissionfunction shows wide peaks and platforms around the Fermi level. While in theatomic-chain/C60/atomic-chain case, the device shows resonant tunneling behavior and the Fermi level lies between theHOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital)transmission peaks. This results in a current that is one order of magnitude smaller than that in thenanowire/C60/nanowire system and the current increases very slowly until the bias is big enough to includethe LUMO peak in the bias window. The big difference in the conductance andthe current arises from the different coupling between the electrodes and theC60 and the different number of channels in the electrodes.

Effect of pinholes in magnetic tunnel junctions

The electron transport in magnetic tunnel junction containing pinholes is studied, where ferromagnetic layers make direct contact through narrow conducting channels. The transport is treated within the Landauer formalism using a tight-binding Hamiltonian. It is found that a narrow pinhole induces a resonant tunneling behavior causing a magnetoresistance that oscillates with the bias voltage. After averaging over pinholes of various shapes, the oscillation and magnitude of magnetoresistance (MR) are reduced, which can explain how barrier roughness diminishes the MR. For a pinhole of a large radius, where the number of atoms inside is much larger than 1, an enhanced MR is obtained whose value is similar to an all-metal giant magnetoresistance spin valve.