Negative Differential Resistance Behavior Research Articles

Defect-engineered room temperature negative differential resistance in monolayer MoS2 transistors.

The negative differential resistance (NDR) effect has been widely investigated for the development of various electronic devices. Apart from traditional semiconductor-based devices, two-dimensional (2D) transition metal dichalcogenide (TMD)-based field-effect transistors (FETs) have also recently exhibited NDR behavior in several of their heterostructures. However, to observe NDR in the form of monolayer MoS2, theoretical prediction has revealed that the material should be more profoundly affected by sulfur (S) vacancy defects. In this work, monolayer MoS2 FETs with a specific amount of S-vacancy defects are fabricated using three approaches, namely chemical treatment (KOH solution), physical treatment (electron beam bombardment), and as-grown MoS2. Based on systematic studies on the correlation of the S-vacancies with both the device's electron transport characteristics and spectroscopic analysis, the NDR has been clearly observed in the defect-engineered monolayer MoS2 FETs with an S-vacancy (VS) amount of ∼5 ± 0.5%. Consequently, stable NDR behavior can be observed at room temperature, and its peak-to-valley ratio can also be effectively modulated via the gate electric field and light intensity. Through these results, it is envisioned that more electronic applications based on defect-engineered layered TMDs will emerge in the near future.

Transport properties of MoS2/V7(Bz)8 and graphene/V7(Bz)8 vdW junctions tuned by bias and gate voltages.

The MoS2/V7(Bz)8 and graphene/V7(Bz)8 vdW junctions are designed and the transport properties of their four-terminal devices are comparatively investigated based on density functional theory (DFT) and the nonequilibrium Green's function (NEGF) technique. The MoS2 and graphene nanoribbons act as the source-to-drain channel and the spin-polarized one-dimensional (1D) benzene–V multidecker complex nanowire (V7(Bz)8) serves as the gate channel. Gate voltages applied on V7(Bz)8 exert different influences of electron transport on MoS2/V7(Bz)8 and graphene/V7(Bz)8. In MoS2/V7(Bz)8, the interplay of source and gate bias potentials could induce promising properties such as negative differential resistance (NDR) behavior, output/input current switching, and spin-polarized currents. In contrast, the gate bias plays an insignificant effect on the transport along graphene in graphene/V7(Bz)8. This dissimilarity is attributed to the fact that the conductivity follows the sequence of MoS2 < V7(Bz)8 < graphene. These transport characteristics are examined by analyzing the conductivity, the currents, the local density of states (LDOS), and the transmission spectra. These results are valuable in designing multi-terminal nanoelectronic devices.

Achieved negative differential resistance behavior of Si/B-substituted into a C6 chain sandwiched between capped carbon nanotube junctions.

Electronic transport properties of a pristine C6 chain and Si/B-substituted into the C6 chain sandwiched between two (5, 5) capped carbon nanotube electrodes were investigated through first-principles calculations based on non-equilibrium Green's functions (NEGF) conjugated with density functional theory (DFT). Si and B substitutions will affect the I–V curve of a pristine C6 chain. In the I–V characteristics, multi negative differential resistance (NDR) with large peak to valley ratio (PVR) and rectifying actions were observed. The NDR behavior originates from the joining and moving of conduction orbitals inside and outside of the bias window at a certain bias voltage. Furthermore, the assessment of transmission coefficient and distribution of molecular orbitals reveals that the rectifying performance is the result of the asymmetric distribution of the frontier molecular orbitals in the central region and their coupling with the electrodes. Multi NDR behavior of B substitution under very low bias voltage is a unique property of our proposed devices. Moreover, the CNT|C–(B–C)2–C|CNT molecular device shows a high PVR up to 31.8, which demonstrates that the proposed devices can be useful for molecular switching in nanoelectronic devices.

Understanding composite negative differential resistance in niobium oxide memristors

Volatile memristors, or threshold switching devices, exhibit a diverse range of negative differential resistance (NDR) characteristics under current-controlled operation and understanding the origin of these responses is of great importance for exploring their potential as nano-scale oscillators for neuromorphic computing. Here we use a previously developed two-zone, parallel memristor model to undertake a systematic analysis of NDR modes in two-terminal metal-oxide-metal devices. The model assumes that the non-uniform current distribution associated with filamentary conduction can be represented by a high current density core and a lower current-density shell where the core is assumed to have a memristive response due to Poole-Frenkel conduction and the shell is represented by either a fixed resistor or a second memristive region. A detailed analysis of the electrical circuits is undertaken using a lumped-element thermal model of the core-shell structure, and is shown to reproduce continuous and discontinuous NDR responses, as well as more complex compound behaviour. Finally, an interesting double-window oscillation behaviour is predicted and experimentally verified for a device with compound NDR behaviour. These results clearly identify the origin of different NDR responses and provide a strong basis for designing devices with complex NDR characteristics.

Investigation of transport behavior in borospherene-based molecular wire for rectification applications

The transport properties of molecular wire comprising of B40 fullerene are investigated by employing density functional theory (DFT) and non-equilibrium green’s function (NEGF) methodology. The quantum transport is evaluated by calculating the density of states, transmission spectra at various bias voltages, molecular energy spectra, HOMO-LUMO gap, current–voltage curve, and transmission pathways. In context to its properties, results show that by increasing the length of molecular wire, the device exhibits rectification ratio and prominent NDR behavior. I–V curve scrutinizes that as the length of wire is increased the curve becomes non-linear. This non-linear behavior is more prominent in the case when the length of wire is increased up to six fullerene cages significant rectification ratio (R.R) and negative differential resistance (NDR) comes into the picture. The excellent negative differential resistance ensures that a device with at least six molecular wires can be used as a tunnel diode.Graphic abstract

Twist Effect on the Electronic and Transport Properties of 1D Helical Carbyne Chains

The electronic and transport properties of 1D helical carbyne chains (HCCs) are investigated in terms of continuum medium mechanics, density functional theory, and nonequilibrium Green's function by modeling a covalently sandwiched HCC connecting two zigzag graphene nanoribbon leads. It is found that the current of the device decreases by up to two orders of magnitude with increasing twisted pitch. The prodigious negative differential resistance (NDR) and rectifying effects are only exhibited in HCCs with multiple coil cycles. Moreover, graphene/HCC junctions with parallel/antiparallel magnetism configurations allow perfect (100%) spin polarization and NDR behaviors and simultaneously realize the switching effect during twisting. The results provide inspiration for the optimal design of nanomaterials and development of high‐performance multifunctional all‐carbon nanodevices.

First-principle investigations of cove edged GaN nanoribbon for nanoscale resonant tunneling applications

This work investigates the impact of cove edges in gallium nitride nanoribbons (GaNNRs) as cove edges nanoribbons are energetically more stable and facilitates further tunability of electronic properties of nanoribbons. Here structural, electronic, and transport properties of cove edged GaNNRs with hydrogen (H) passivation are investigated. For this investigation, the framework of non-equilibrium Green function (NEGF) formalism based on density functional theory (DFT) has been deployed. The effect of cove edge at nitrogen (N), gallium (Ga), and at both the edges for its potential ultra-scaled device applications are studied. As compared to the pristine semiconducting nature of H–GaN–H, present DFT-based calculations of cove edged GaNNRs exhibit a metallic nature via selective H-passivation. A comparative study of binding energy (Eb) revealed that the C–GaN–H nanoribbon is structurally more stable irrespective of the width in all considered cove edged GaNNRs. Interestingly, the proposed two-terminal cove edged GaNNRs devices exhibit negative differential resistance (NDR) effect based on selective edge passivation with hydrogen atoms. The observed NDR behavior suggests that cove edged GaNNRs with selective H-passivated GaNNRs have immense potential applications for preparing nanoscale NDR devices.

Disconnected N-doped zigzag ZnO nanoribbon for potential Negative Differential Resistance (NDR) applications

Quantum coherence and non-equilibrium statistics are the governing mechanisms for electronic transport in 2-D materials. The present work investigates the electronic transport properties of pristine and N-doped disconnected zigzag ZnO nanoribbons (Z-ZnONRs) using density functional theory (DFT) framework along with non-equilibrium Green’s function (NEGF). Interestingly, even though the structures are disconnected, still they exhibit electron transport. These ZnONRs disconnected structures can act as two probe devices by deploying the tunneling mechanism for electron transport. It is reported that the tunneling current decreases with an increase in the disconnected distance between the two considered Z-ZnONR structures. Further, negative differential resistance (NDR) characteristics are observed in all the considered configurations. Moreover, the N atom doping is also studied at the disconnected edges. N-dopant position affects the I–V characteristics based on the dopant sites. Zn-rich edge dopant induces NDR across a wide range while O-rich edge dopant induces linear I–V behavior with lower NDR characteristics. The highest NDR peak-to-valley current ratio is reported around 5.6 ×104 within the 0.15 V bias region. The structure with N doped at both edges and disconnected distance as 0.5 Å exhibited dominant NDR behavior. This finds their potential use in the design of oscillators, switches, rectifiers, amplifiers, frequency converters, detectors, and resonator circuits, etc.

Tunable Negative Differential Resistance and Resistive Switching Properties of Amorphous WOₓ Devices

The development of multifunctional electric device is of great significance for improving the integration dense of integrated circuits in the future. Herein, amorphous WO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> -based memristor was fabricated and the mechanism of resistance switching was studied in detail. The device exhibited a stable coexistence of bipolar resistive switching (RS) and negative differential resistance (NDR) behaviors at room temperature, which could modulated by changing the annealing time at 300 °C. The optimal high-resistance state (HRS)/low-resistance state (LRS) resistance ratio of ~30 was obtained by postannealing in 100 min. However, both RS and NDR behaviors disappeared with the crystallization of amorphous films when the annealing time was 300 min. The Ohmic conduction mechanism should be responsible for the charge transport of LRS, while the HRS transmission was corporately dominated by the trap-controlled space charge limited conduction (SCLC) and Poole-Frenkel (P-F) emission. The change of trap levels modulated by postannealing was calculated and considered to be the reason for the change of RS and NDR behaviors. Raman spectroscopy provided evidence for the formation of strong W-O bonds, which contributed to the disappearance of RS and NDR behaviors.

Negative differential resistance in all-benzene molecule of trefoil knot

Based on first-principles calculations, the electronic transport of a recently synthesized all-benzene molecule of trefoil knot is investigated, by contacted with Au electrodes. Negative differential resistance behavior is observed. Further analysis shows that, it is resulted from the weaken of the states on the molecule modulated by the bias voltage, which suppresses the transmission eigenchannels and transmission peaks. Moreover, such a NDR behavior is also found in knot molecules with more benzene rings, indicating NDR is the intrinsic feature of such kind of molecules and robust to the number of benzene rings. These findings are expected to be extended to many other molecules with similar geometries, and may throw light on the development of future nanodevices.

Gate-Tunable Negative Differential Resistance Behaviors in a hBN-Encapsulated BP-MoS2 Heterojunction.

Two-dimensional (2D) heterostructures show great potential in achieving negative differential resistance (NDR) effects by Esaki diodes and or resonant tunneling diodes. However, most of the reported Esaki diode-based NDR devices realized by bulk 2D films lack sufficient gate tunability, and the tuning of NDR behavior from appearing to vanishing remains elusive. Here, a gate-tunable NDR device is reported based on a vertically stacked black phosphorus (BP) and molybdenum disulfide (MoS2) thin 2D heterojunction. At room temperature, a rectifying ratio of ∼6 orders of magnitude from a reverse rectifying diode to a forward rectifying diode by gate modulation is obtained. Through analyzing the temperature-dependent electrical properties, the tunneling mechanism at a certain gate voltage range is revealed. Moreover, the switchable and continuously gate-tunable NDR behavior is realized with a maximum peak-to-valley ratio of 1.23 at 77 K, as shown in the IDS mappings by sweeping VDS under different VGS. In addition, a compact model for gate-tunable NDR behavior in 2D heterostructures is proposed. To our best knowledge, this is the first demonstration of NDR behavior in BP-MoS2 heterostructures. Consequently, this work sheds light on the gate-tunable NDR devices and reconfigurable logic devices for realizing ternary and reconfigurable logic systems.

Negative Differential Resistance in Carbon-Based Nanostructures

Nonlinear electrical properties, such as negative differential resistance (NDR), are essential in numerous electrical circuits, including memristors. Several physical origins have been proposed to lead to the NDR phenomena in semiconductor devices in the last more than half a century. Here, we report NDR behavior formation in randomly oriented graphene-like nanostructures up to 37 K and high on-current density up to 10^5 A/cm^2. Our modeling of the current-voltage characteristics, including the self-heating effects, suggests that strong temperature dependence of the low-bias resistance is responsible for the nonlinear electrical behavior. Our findings open opportunities for the practical realization of the on-demand NDR behavior in nanostructures of 2D and 3D material-based devices via heat management in the conducting films and the underlying substrates.

Tuning the electronic structures and anisotropic transport behaviors of GeSe monolayer by substitutional doping

The electronic structures and anisotropic transport properties of doped-GeSe monolayers are systematically explored by performing the density functional theory combined with non-equilibrium Green’s function method. Numerical results of the cohesive energy and formation energy show that it is possible to substitute Ge/Se with isovalent atoms and group-V atoms at room temperature. Isovalent substitutions of Ge/Se atoms can maintain the semiconducting features of monolayer GeSe. While the doping of group-V atoms modifies drastically the electronic structures of doped-GeSe and makes metallic properties appear. In addition, the anisotropy of electronic transport of monolayer GeSe also can be effectively manipulated by substitutional doping. In particular, the isotropic electronic transport properties are shown in the devices based on GeSe with P substituting Ge atom. An obvious negative differential resistance behavior with a large current peak-to-valley ratio up to the radio of 103 is gained in N-dope device. These results are useful for the future potential applications of GeSe materials in next-generation high-efficiency electronic devices.

The transformation of digital to analog resistance switching behavior in Bi2FeCrO6 thin films

ABSTRACT Bi2FeCrO6 (BFCO) thin films were fabricated by sol-gel method. Digital and analog resistive switching behaviors were sequentially observed in Au/BFCO/FTO/Glass structure by applying a continuous cyclic voltage. By analyzing formation mechanism of the two types of the resistive switching behaviors, it is found that the digital resistive behavior conductance mechanism is a bulk-limited conduction, and the analog resistive switching behavior is accompanied with rectification effects and negative differential resistance behaviors, which are considered as interface-limited conductivity behaviors. So the change of digital and analog resistive switching behaviors may be result of the transformation of conductive mechanism. These research results will help us to design and manufacture digital and analog multifunctional resistive switching memory devices.

Structural & electronic properties of zigzag silicene nanoribbons with symmetric/asymmetric edge passivations via fluorine and hydrogen

The intriguing properties of silicene nanoribbons indicate potential applications in nanoelectronic devices. The first-principles calculation based on density functional theory has been performed to investigate the structural, electronic and magnetic properties of asymmetric (sp3-sp2) and symmetric (sp3-sp3) edge functionalized zigzag silicene nanoribbons (ZSiNR). The structural analysis reveals that fully fluorinated ZSiNR for both asymmetric and symmetric edge functionalized ZSiNRs are energetically more stable irrespective of ribbon width. For selective structures, the magnetic ground state is found to be robust against thermal excitations at room temperature (25 meV) indicating their potential for practical applications. Moreover, bipolar magnetic semiconductor and half-metallic behavior have been observed in spin-based band structure calculations. Further, the spin-dependent transport properties of ZSiNR have been performed using the two-terminal device model which produces negative differential resistance (NDR) behavior due to spin-down current. This investigation reveals the immense capabilities of fluorine symmetric and asymmetric termination to modulate the electronic and spintronic properties of ZSiNR. Thus, the present work can pave the way for futuristic electronics and spintronics nanodevices.

Ballistic transport and optical properties of a new half-metallic monolayer: Vanadium phosphide

In this work, a new monolayer structure, vanadium phosphide (VP) was predicted by first principles approach. Dynamical and thermal stabilities of monolayer VP were confirmed by phonon dispersion and ab initio molecular dynamics calculations. Monolayer VP was found as half-metallic material with an electronic band gap of 1.73 eV in spin down channel, while up spins display metallic band structure yielding a spin-polarized conductivity. However, an applied electric field in perpendicular-to-plane direction gradually reduces the band gap value. The current-voltage analysis indicates negative differential resistance behavior at room temperature. Besides, high optical conductivity is remarkable for optoelectronic applications. The geometric and electronic structures of bilayer VP, MoS2/VP and bP/VP heterostructures were also revealed. The half-metallic nature of pristine VP is preserved in bilayer form with indirect-to-direct band gap transition in spin down channel, which is an important implication for band gap engineering and practical device applications. The novel VP monolayer system has rich functional properties as a promising 2D material.

Room temperature negative differential resistance in clay-graphite paper transistors

Paper electronics have been fast developed in recent years due to their degradability and recyclability; however, most of them are barely equipped with logic functions, impeding them from becoming autonomous on-paper systems. To provide a working unit for logic implementations, a paper field-effect transistor (FET) with a clay-graphite channel that demonstrated negative differential resistance (NDR) is fabricated in this study. The device exhibited a p-type semiconductor characteristic with an optical bandgap of ∼1.97 eV according to photoluminescence analysis, resulting from considerable defective graphite mixed with clay in the channel. Considering that the NDR behavior is theoretically predicted to be tunable by the contact resistance, we fabricated FETs with different contact resistances and observed that the NDR behavior occurred in devices with relatively lower contact resistance. The NDR effect is also tunable by varying the gate voltage, which matches well with simulation results. The possible mechanism for the NDR behavior is the decrease in carrier drift velocity induced by band-to-band tunneling, associated with impurities-induced trapping states and gate-induced confined states. This work provides a promising and easy pathway to develop digital components using paper electronics in the near future.

Charge transport in polythiophene molecular device: DFT analysis.

We report the charge transport phenomenon in polythiophene molecular device and the ways of controlling the nature of charge transport through the device. By using density functional theory (DFT) and non-equilibrium Green's function (NEGF) formalisms, two ways of controlling the nature of charge transport have successfully been demonstrated by introducing conformational changes in the channel and applying external gate potential. Functional groups with negative mesomeric effect such as nitrous and carboxyl and positive mesomeric effect such as amino have been used as substituents as part of introducing conformational changes in the channel. The results indicate that the nature of charge transport in polythiophene molecular device can be changed from hole dominant to electron dominant and vice versa just by introducing minor conformational changes in the channel and by changing the polarity of external gate potential. Moreover, the negative differential resistance (NDR) behavior has been observed in amino-substituted thiophene device. These findings will be very useful in understanding the design of both p and n-type transistors out of same molecule for the next-generation molecular electronics.

Rectifying and spin filtering behavior of aluminum doped silicon carbide nanoribbons: the first principles study

In this paper, spin transport properties of aluminum-doped zigzag silicon carbide nanoribbons (Al-ZSiC NRs) are investigated using the first-principle calculations and the nonequilibrium Green’s function method. The results show an approximately perfect spin filtering (100%) for three considered models and undoped structure at ferromagnetic state in the presence of bias voltage. In particular, a weak negative differential resistance (NDR) phenomenon can be obtained in a certain system when replacing the edge Si atom with the Al-doping atom. Indeed, edge states play a crucial role in spin-dependent transport and magnetic properties of ZSiC NRs, such as the NDR effect. Furthermore, the significant rectifying ratio (RR) is obtained under bias voltage only for one given configuration. When the same spin states overlap in the bias window (BW), spin-dependent transmission and the spin current display a non-zero value; however, the mismatch of the same spin states within the BW region causes to vanish the transmission spectra. The controllable manipulation of threshold voltage, spin filtering efficiency, NDR behavior, and RR effect can be achieved by substituting of silicon with Al atom in ZSiC NRs. These results shed new light on our understanding of silicon carbide-based nanodevices with appealing spintronic applications.

γ-Graphyne rectifier and NDR tunable by doping, line edge roughness and twist

The armchair γ-graphyne nanoribbon (A-γ-GyNR) based on doping boron and nitrogen atoms in left and right leads, respectively, was proposed as the initial sample of a rectifier device. Afterwards, the next five devices were presented by applying line edge roughness (LER) defect, increasing its roughness, doping concentration, and its position and twisting under six different angles to the center of the initial model. Also, the effect of width was investigated. The computational method for investigating the electronic transfer properties was a combination of the non-equilibrium Green’s function (NEGF) and the tight binding method. The current curve and transmission spectrum revealed the negative differential resistance (NDR) behavior, which underwent the most changes under the influence of LER. Density of state (DOS) peaks indicated that p-orbital had a more significant effect on transmission in all devices; on the other hand, the localization of molecular projected self-consistent Hamiltonian (MPSH) structure in positive biases resulted from the suppression of electron tunneling. Based on the findings, the maximum rectification ratio in the M″3 device, twisted by an angle of 75°, was equal to 5.86 × 108, which was 41.2 times higher than that of the initial sample; the highest NDR value of the M′1 device was 56.