Presence Of Negative Differential Resistance Research Articles

Interfacial traps and band offset enabled charge separation facilitating current/capacitance hysteresis in dual-oxide layered structure

Gradual switching in the memristor or memcapacitor devices is the key parameter for the next generation of bio-inspired neuromorphic computing. Here, we have fabricated the WOx/ZrOx dual-oxide layered device, which shows the coexistence of gradual resistive and capacitive switching arisen from the current and capacitance hysteresis curves, respectively. The expansion of hysteresis loop can be modulated by altering the oxygen content in the oxide materials. Interestingly, the presence of negative differential resistance (NDR) is dependent on the voltage sweep direction and range of applied bias, which can be reasoned by the local electric field, charge trapping/detrapping, and conduction band offset at the dual-oxide interface. This study provides the concept of the coexistence of current and capacitance hysteresis along with NDR, and it is highly potential for memristor and memcapacitor circuits to explore neuromorphic computing.

Electrochemical oscillations during the oxidation of 2-(dimethylamino)ethanethiol

• The electrochemical oxidation of DMAET led to oscillations in current and potential. • Electrochemical impedance spectroscopy was used to confirm the presence of negative differential resistance. • High frequency oscillations were observed under potentiostatic conditions. • The system supports complexity in the form of bursting and mixed-mode oscillations. This paper describes the electrochemical oxidation of 2-(dimethylamino)ethanethiol (DMAET), a known hydrolysis product of V-type nerve agents, which can be used to mimic the behavior of chemical warfare agents. Interestingly, during its oxidation, two distinct regions of dynamic (i.e., oscillatory) behavior were uncovered. Mechanistic investigation using electrochemical impedance spectroscopy (EIS) lead to the discovery that one of the oscillatory regions was driven by the presence of negative differential resistance (NDR) and that the occurrence of the other was dependent on the concentration of supporting electrolyte. EIS measurements indicated that the DMAET electrochemical oscillator belongs to the HN-NDR class of oscillators, which was supported by the presence of sustained oscillations in both current (under potentiostatic conditions) and potential (under galvanostatic conditions). Furthermore, the oxidation of DMAET on platinum electrodes resulted in rich dynamical behavior in the form of complex bursting phenomena.

Current Rectification, Resistive Switching, and Stable NDR Effect in BaTiO3/CeO2 Heterostructure Devices

AbstractElectronic devices with simultaneous manifestation of multiphysical properties are of great interest due to their possible application in multifunctional devices. In the present study, simultaneous execution of negative differential resistance (NDR) effect, current rectification (≈105), and resistive switching characteristics (≈103) are demonstrated in BaTiO3/CeO2 heterostructure. Although the negative differential effect has gained huge attention, its instability and poor reproducibility at room temperature are the main obstacles to its possible application in electronic devices. However, in this report, the NDR is observed even after hundreds of cycles in BaTiO3/CeO2 heterostructure at 300 K. For a detailed analysis of the NDR effect, AC conductance spectroscopy is performed, which reveals that the presence of NDR is associated with trapping/detrapping of charge carriers at interface states formed at the BaTiO3/CeO2 interface. In addition, the resistive switching and rectification effect are demonstrated due to a barrier at the BaTiO3/CeO2 interface, which can be strongly modulated by thickness (20, 50, and 80 nm) based ferroelectric polarization of BaTiO3. However, the results show that the remarkable performance of these devices makes them a potential candidate for application in multifunctional devices.

Photo assisted negative differential resistance in porous silicon: A potential nano-structure for hot carrier solar cell

Abstract A device, supporting negative differential resistance, has been fabricated. Aluminum top contacts have been deposited on electrochemically synthesized porous silicon layer on p-type silicon substrate for this purpose. Top-bottom DC current vs. voltage (I-V) characteristics of the fabricated device have been recorded at room temperature under dark condition and injecting photons. Dark I-V characteristics of this device indicate the presence of negative differential resistance (NDR). Similar kind of I-V characteristics has been observed under illumination. At the same time, fabricated device shows photovoltaic effect after injecting photons. This may be due to some series and parallel combination of multiple junctions with photovoltaic nature.

Insights into negative differential resistance in MoS2 Esaki diodes: A first-principles perspective

\ce{MoS_2} is a two dimensional material with a band gap depending on the number of layers and tunable by an external electric field. The experimentally observed intralayer band-to-band tunneling and interlayer band-to-band tunneling in this material present an opportunity for new electronic applications in tunnel field effect transistors. However, such a widely accepted concept has never been supported up by theoretical investigations based on first principles. In this work, using density functional theory, in conjunction with non-equilibrilibrium Green's function techniques and our electric field gating method, enabled by a large-scale computational approach, we study the relation between band alignment and transmission in planar and side-stack \ce{MoS_2} $p$-$i$-$n$ junction configurations. We demonstrate the presence of negative differential resistance for both in-plane and interlayer current, a staple characteristic of tunnel diode junctions, and analyze the physical origin of such an effect. Electrostatic potentials, the van der Waals barrier, and complex band analysis are also examined for a thorough understanding of Esaki Diodes.

Coexistence of room-temperature negative differential resistance, negative photoconductivity modulated by UV light intensity and optical switching in Cu/Ni:ZnO/InGa structure

Cu/Ni:ZnO/InGa structure has been fabricated by depositing the chemically synthesized Ni:ZnO nanoparticles on glass substrate. The device shows a negative differential resistance (NDR) effect and negative photoconductivity (NPC) at room temperature. The presence of NDR is attributed to the electrons trapped/detrapped by interface states at Cu/Ni:ZnO junction. The origin of NPC is understood in term of competition between carriers injection due to the external field and photocarriers due to the external optical signal. Thus, these two effects (NDR and NPC) contribute to the optical switching process found in our device.

Anomalous current–voltage and impedance behaviour in doped Poly 3-methylthiophene devices

Current–voltage (I–V) and impedance measurements are performed on electrochemically-doped poly(3-methylthiophene) (P3MeT) devices in metal/polymer/metal sandwich geometry. The detailed investigation shows the presence of negative differential resistance (NDR) in the sandwich devices with different metals in action as substrate and top electrode. It is found that the reiteration of I–V measurements significantly enhances the NDR. The P3MeT devices shows a considerable switching behaviour with ON to OFF ratio varying between two to three order but lacks the consistency in bias stress test. An anomalous behaviour in the impedance measurements in the form of a prolonged tail is observed in Cole–Cole plots towards lower frequency region, which gets more prominent with applied bias. This impedance anomaly is explained in terms of large distribution of relaxation times arising due to long lived trap states at the bulk and interface which is correlated with the NDR observed in P3MeT devices.

The effects of the applied current and the measurement temperature on the negative differential resistance behaviour of carbonized xerogel

Electrical properties of carbonised organic xerogel based on resorcinol–formaldehyde (RF), prepared by pyrolysis at 675 °C in nitrogen atmosphere for two hours, were investigated. In this temperature an insulator to semiconductor-like transition occurs. The voltage–current (V–I) characteristics indicate the presence of non-linear conductivity depending on the measurement temperature. The origin of the non-linearity in the electrical conductivity is discussed using different theoretical models. The obtained results reveal that this non-linear conductivity starts above a threshold current, which is illustrated by the presence of negative differential resistance (NDR) region. The properties of the obtained NDR are controlled by the applied current and are attributed to a percolation phenomenon in the carbonised sample. The obtained result is very promising for many applications in power electronic technology specially for the development of some negatronic devices.

Synthesis and Characterization of Porous Carbon/Nickel Oxide Nanocomposites for Gas Storage and Negatronic Devices

Porous organic/inorganic nanocomposites were synthesized by sol–gel technique after the incorporation of nickel oxide (NiO) nanoparticles in carbon composite based on pyrogallol and formaldehyde (PF) using picric acid as catalyst. After a drying step, the samples were heated during 2 h at different pyrolysis temperatures from 600 to 1000 °C in tubular furnace under nitrogen atmosphere. The XRD pattern exhibit that PF composite is amorphous even after thermal treatment at 1000 °C. On the other hand, the PF/NiO nanocomposites are crystallized with the appearance of the graphite structure at high pyrolysis temperature. The gas adsorption capacities for CO2 indicate that the PF composite has a tendency to adsorb CO2 higher than PF/NiO nanocomposite. In fact, the maximum value of capacity is of the order 7.5 mmol/g in PF composite and 6.5 mmol/g in PF/NiO nanocomposite. The dc conductivity shows the dominance of percolation phenomenon and explained by two models; the three dimensions variable range hopping and the nearest neighbor hopping. The voltage–current V(I) characteristics show the presence of negative differential resistance at room measurement temperature in PF/NiO-625 °C sample. The ac conductance is attributed to different origins, so it is decried by two models, like hopping conduction mechanism in PF-675 °C composite and small polaron hopping model in PF/NiO-625 °C nanocomposite.

Origin of dc and ac electric transport phenomena in carbon/manganese oxide nanocomposite

Hybrid organic/inorganic nanocomposites based on manganese oxide nanoparticles enriched pyrogallol-formaldehyde matrix (PF/MnO) were synthesized by sol-gel technique. After a drying step, the samples were heated during 2 h at different pyrolysis temperatures between 600 and 1000 °C in tubular furnace under open nitrogen atmosphere. The obtained nanocomposites were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and electrical technics in the measurement temperature range between 80 and 300 K. The XRD spectra show that PF/MnO nanocomposites are crystallized with the appearance of different phases: the graphite (C), the manganese oxide (MnO), the metallic manganese (Mn) and the manganese dioxide (MnO2) with proportions depending on pyrolysis temperature. The measurement temperature dependence conductivity can be explained by Godet-Variable Range Hopping (3D-GVRH) conduction model in all samples with the presence of an exponential distribution of localized states. The voltage-current V(I) characteristics show the presence of negative differential resistance (NDR) in some samples. The ac conductance exhibits the dominance of hopping conduction mechanism and the Small Polaron Hopping (SPH) model. The Nyquist plots for the PF/MnO-650 °C nanocomposite obey at Cole-Cole model. The impedance spectra were fitted by an equivalent circuit involving two contributions attributed to grains and grain boundaries.

Transport Properties of a MoS2/WSe2 Heterojunction Transistor and Its Potential for Application

This paper studies band-to-band tunneling in the transverse and lateral directions of van der Waals MoS2/WSe2 heterojunctions. We observe room-temperature negative differential resistance (NDR) in a heterojunction diode comprised of few-layer WSe2 stacked on multilayer MoS2. The presence of NDR is attributed to the lateral band-to-band tunneling at the edge of the MoS2/WSe2 heterojunction. The backward tunneling diode shows an average conductance slope of 75 mV/dec with a high curvature coefficient of 62 V(-1). Associated with the tunnel-diode characteristics, a positive-to-negative transconductance in the MoS2/WSe2 heterojunction transistors is observed. The transition is induced by strong interlayer coupling between the films, which results in charge density and energy-band modulation. The sign change in transconductance is particularly useful for multivalued logic (MVL) circuits, and we therefore propose and demonstrate for the first time an MVL-inverter that shows three levels of logic using one pair of p-type transistors.

Band structure effects on resonant tunneling in III-V quantum wells versus two-dimensional vertical heterostructures

Since the invention of the Esaki diode, resonant tunneling devices have been of interest for applications including multi-valued logic and communication systems. These devices are characterized by the presence of negative differential resistance in the current-voltage characteristic, resulting from lateral momentum conservation during the tunneling process. While a large amount of research has focused on III-V material systems, such as the GaAs/AlGaAs system, for resonant tunneling devices, poor device performance and device-to-device variability have limited widespread adoption. Recently, the symmetric field-effect transistor (symFET) was proposed as a resonant tunneling device incorporating symmetric 2-D materials, such as transition metal dichalcogenides (TMDs), separated by an interlayer barrier, such as hexagonal boron-nitride. The achievable peak-to-valley ratio for TMD symFETs has been predicted to be higher than has been observed for III-V resonant tunneling devices. This work examines the effect that band structure differences between III-V devices and TMDs has on device performance. It is shown that tunneling between the quantized subbands in III-V devices increases the valley current and decreases device performance, while the interlayer barrier height has a negligible impact on performance for barrier heights greater than approximately 0.5 eV.

All-Graphene Planar Double Barrier Resonant Tunneling Diodes

In this work, we propose an atomically-thin all-graphene planar double barrier resonant tunneling diode that can be realized within a single graphene nanoribbon. The proposed device does not require any doping or external gating and can be fabricated using minimal process steps. The planar architecture of the device allows a simple in-plane connection of multiple devices in parallel without any extra processing steps during fabrication, enhancing the current driving capabilities of the device. Quantum mechanical simulation results, based on non-equilibrium Green's function formalism and the extended Huckel method, show promising device performance with a high reverse-to-forward current rectification ratio exceeding 50 000, and confirm the presence of negative differential resistance within the device's current-voltage characteristics.

Study of negatronic device based on amorphous carbon/nickel nanocomposite

Abstract Composite based on pyrogallol and formaldehyde (PF) reached by NiO nanoparticles has been prepared using sol–gel method to obtain negatronic PF/Ni devices. The obtained materials were subjected to heat treatment under inert atmosphere at 650 °C for 2 h. The X-ray diffraction analysis (XRD) shows that PF sample was composed of amorphous material while PF/Ni XRD spectra exhibited the presence of metallic nickel characteristic lines. The transmission electron microscopy (TEM) images indicate that PF sample was formed by homogenous material, and metallic nickel nanoparticles sized around 30 nm were dispersed in the PF/Ni nanocomposite. dc I ( V ) characteristics indicate a symmetric and non-linear behavior and the presence of negative differential resistance (RDN) phase in the PF/Ni sample. The dc conductivity ( σ dc ) can be explained by Variable Range Hopping (3D-VRH) conduction model in both samples. The ac conductance shows the dominance of hopping conduction mechanism in PF sample; however, the Correlated Barrier Hopping (CBH) model seems to be dominant in the PF/Ni nanocomposite. The Nyquist plots were used to identify an equivalent circuit with the aim to study the possible contribution of the grains and boundary grains to the samples conductivities.

Effects of Vacancies on the Electron Transport in Semiconducting Zigzag Carbon Nanotubes

Since the advent of nanoscale material based electronic devices, there has been a considerable interest in exploring carbon nanotubes from fundamental science and technological perspectives. In carbon nanotubes, the atoms form a cylindrical structure with a diameter of the order 1nm. The length of the nanotubes can extend up to several hundred micrometers. Carbon nanotubes exhibit a variety of intriguing electronic properties such as semiconducting and metallic behaviour, due to the quantum confinement of the electrons in the circumferential direction. Much of the study dedicated to describe the behaviour of carbon nanotube-based devices assumes for simplicity the nanotube to be a ballistic material. However, in reality the phonon scattering mechanism exists also in nanotubes, of course, and can generally not be neglected, except in very short nanotubes. In this work, we focus attention on exploring the steady-state electron transport properties of semiconducting single-walled carbon nanotubes, including both phonon scattering and defect (vacancy) scattering, using the semi-classical bulk single electron Monte Carlo method. The electron energy dispersion relations are obtained by applying the zone folding technique to the dispersion relations of graphene, which are calculated using the tight-binding description. The vibrational modes in the carbon nanotubes are studied using a fourth nearest-neighbour force constant model. Both the electron-phonon and the electron-defect interactions are formulated within the tight-binding framework, and their corresponding scattering rates are computed and analyzed. In particular, the dependence of the phonon scattering rate and the defect scattering rate on the diameter of the nanotube, on temperature and on electron energy is studied. It is shown that the differences observed in the scattering rate between different nanotubes mainly stem from the differences in their band structure. A bulk single electron Monte Carlo simulator was developed to study the electron transport in semiconducting zigzag carbon nanotubes. As a first step, we included only electron-phonon scattering, neglecting all other possible scattering mechanisms. With this scattering mechanism, the steady-state drift velocity and the mobility for the nanotubes (8,0), (10,0), (11,0), (13,0) and (25,0) were calculated as functions of the electric-field strength and lattice temperature, and the results are presented and analysed here. The dependence of the mobility on the lattice temperature can be clearly seen at low electric-field strengths. At such electric-field strengths, the scattering is almost entirely due to acoustic phonons, whereas at high electric-field strengths optical phonon emission processes dominate. It is shown that the saturation of the steady-state drift velocity at high electric-field strengths is due to the emission of high-energy optical phonons. The results indicate the presence of Negative differential resistance for some of the nanotubes considered in this work. The discrepancy found in the literature concerning the physical reason for the appearance of negative differential resistance is clarified, and a new explanation is proposed. It is also observed that the backward scattering is dominant over the forward scattering at high electric-field strengths. We then included also defect scattering, actually electron-vacancy scattering, for the nanotubes (10,0) and (13,0). The steady-state drift velocities for these nanotubes are calculated as functions of the density of vacancies, electric-field strength and the lattice temperature, using three different vacancy concentrations. The results indicate the presence of Negative differential resistance at very low concentration of defects, and how this feature may depend on the concentration of defects. The dependence of the steady-state drift velocity on the concentration of defect and the lattice temperature is discussed. The electron distribution functions for different temperatures and electric field strengths are also calculated and investigated for all the semiconducting nanotubes considered here. In particular, a steep barrier found in the electron distribution function is attributed to the emission of high energy optical phonons.

High-field electron transport in semiconducting zigzag carbon nanotubes

Electron transport in semiconducting zigzag carbon nanotubes is studied by solving the Boltzmann transport equation using the single-particle Monte Carlo technique. The electronic band structure is based on a standard nearest-neighbour tight-binding parameterization, and the phonon spectrum is calculated using a fourth nearest-neighbour force constant model. The electron–phonon scattering probabilities are calculated within a tight-binding formalism. The steady-state drift velocities for the semiconducting zigzag nanotubes (8, 0), (10, 0), (11, 0), (13, 0), and (25, 0) are computed as functions of electric field strength and temperature, and the results are analysed here. The results show the presence of negative differential resistance at high electric fields for some of the nanotubes. The drift velocity and the low-field mobility reach a maximum value of ≅ 4.67 × 107 cm s−1 and≅ 4 × 104 cm2 V −1 s−1, respectively, for a (25, 0) nanotube.

Electron–Phonon Scattering Rates in Semiconducting Zig-Zag Carbon Nanotubes

Since the advent of nanoscale material based electronic devices, there has been a considerable interest in exploring carbon nanotubes from fundamental science and technological perspectives. In carbon nanotubes, the atoms form a cylindrical structure with a diameter of the order 1nm. The length of the nanotubes can extend up to several hundred micrometers. Carbon nanotubes exhibit a variety of intriguing electronic properties such as semiconducting and metallic behaviour, due to the quantum confinement of the electrons in the circumferential direction. Much of the study dedicated to describe the behaviour of carbon nanotube-based devices assumes for simplicity the nanotube to be a ballistic material. However, in reality the phonon scattering mechanism exists also in nanotubes, of course, and can generally not be neglected, except in very short nanotubes. In this work, we focus attention on exploring the steady-state electron transport properties of semiconducting single-walled carbon nanotubes, including both phonon scattering and defect (vacancy) scattering, using the semi-classical bulk single electron Monte Carlo method. The electron energy dispersion relations are obtained by applying the zone folding technique to the dispersion relations of graphene, which are calculated using the tight-binding description. The vibrational modes in the carbon nanotubes are studied using a fourth nearest-neighbour force constant model. Both the electron-phonon and the electron-defect interactions are formulated within the tight-binding framework, and their corresponding scattering rates are computed and analyzed. In particular, the dependence of the phonon scattering rate and the defect scattering rate on the diameter of the nanotube, on temperature and on electron energy is studied. It is shown that the differences observed in the scattering rate between different nanotubes mainly stem from the differences in their band structure. A bulk single electron Monte Carlo simulator was developed to study the electron transport in semiconducting zigzag carbon nanotubes. As a first step, we included only electron-phonon scattering, neglecting all other possible scattering mechanisms. With this scattering mechanism, the steady-state drift velocity and the mobility for the nanotubes (8,0), (10,0), (11,0), (13,0) and (25,0) were calculated as functions of the electric-field strength and lattice temperature, and the results are presented and analysed here. The dependence of the mobility on the lattice temperature can be clearly seen at low electric-field strengths. At such electric-field strengths, the scattering is almost entirely due to acoustic phonons, whereas at high electric-field strengths optical phonon emission processes dominate. It is shown that the saturation of the steady-state drift velocity at high electric-field strengths is due to the emission of high-energy optical phonons. The results indicate the presence of Negative differential resistance for some of the nanotubes considered in this work. The discrepancy found in the literature concerning the physical reason for the appearance of negative differential resistance is clarified, and a new explanation is proposed. It is also observed that the backward scattering is dominant over the forward scattering at high electric-field strengths. We then included also defect scattering, actually electron-vacancy scattering, for the nanotubes (10,0) and (13,0). The steady-state drift velocities for these nanotubes are calculated as functions of the density of vacancies, electric-field strength and the lattice temperature, using three different vacancy concentrations. The results indicate the presence of Negative differential resistance at very low concentration of defects, and how this feature may depend on the concentration of defects. The dependence of the steady-state drift velocity on the concentration of defect and the lattice temperature is discussed. The electron distribution functions for different temperatures and electric field strengths are also calculated and investigated for all the semiconducting nanotubes considered here. In particular, a steep barrier found in the electron distribution function is attributed to the emission of high energy optical phonons.

Optimized minigaps for negative differential resistance creation in strongly δ-doped (1D) superlattices

The ‘atomic saw method’ uses the passage of dislocations in two-dimensional (2D) quantum-well superlattices to create periodic slipping layers and one-dimensional (1D) quantum wire superlattices. The effects of this space structuring of the samples on the allowed energies are analysed in the case of GaAs δ-doped superlattices. If they are sufficiently large, the various minigaps appearing in the 1D band structure could be responsible for the presence of negative differential resistance (NDR) with high critical current in these systems. The purpose is to determine the evolution of the minigaps in terms of the sample parameters and to obtain the means to determine both the 2D and 1D structural characteristics where NDR could appear.

Stability of characteristic curves of nonlinear resistive circuits

In this paper, we discuss the stability of the characteristic curves for nonlinear resistive circuits including parasitic elements. Although the dc solution is determined by analyzing the nonlinear resistive circuit, its equilibrium point will be stable or unstable because every resistive element has a small parasitic component in practice. We consider here two parasitic elements: a capacitor between every resistor node and ground and an inductor in series with each resistor. Of course, the stability can be decided by solving the variational equation at each equilibrium point obtained by the dc analysis; however, this is very time consuming. We show here that the stability is mainly changed at the boundary of the presence of negative differential resistance (NDR) and the bifurcation points, such as turning and pitchfork points on the dc characteristic curves. The instability regions of the solution curve are easily found by both the locations of bifurcation points and NDR regions of the nonlinear resistors.

Nonequilibrium phenomena in nonsymmetrical superconducting double-barrier structure Nb/NbOx/Al/AlOx/Nb

Tunneling structure Nb/NbOx/Al/AlOx/Nb with thin barrier in the Nb/NbOx/Al junction and 4–6 nm thick Al interlayer was prepared and experimentally studied. Pair breaking at the tunneling processes in one junction produces nonequilibrium state of quasiparticle density in Al interlayer and consequently nonequilibrium tunneling processes in the whole structure. All joined effects, namely gap voltage suppression, presence of negative differential resistance at gap voltage and effects induced by applying of microwave radiation are similar to those observed on stacked Nb/Al/AlOx/Nb tunnel junction current-voltage characteristics. Results may be used for the interpretation of behavior of high current density SNS or SIS type multilayers of low and high temperature superconductor structures.