Origin Of Negative Differential Resistance Research Articles

Physical Origin of Negative Differential Resistance in V3 O5 and Its Application as a Solid-State Oscillator.

Oxides that exhibit an insulator-metal transition can be used to fabricate energy-efficient relaxation oscillators for use in hardware-based neural networks but there are very few oxides with transition temperatures above room temperature. Here the structural, electrical, and thermal properties of V3 O5 thin films and their application as the functional oxide in metal/oxide/metal relaxation oscillators are reported. The V3 O5 devices show electroforming-free volatile threshold switching and negative differential resistance (NDR) with stable (<3% variation) cycle-to-cycle operation. The physical mechanisms underpinning these characteristics are investigated using a combination of electrical measurements, in situ thermal imaging, and device modeling. This shows that conduction is confined to a narrow filamentary path due to self-confinement of the current distribution and that the NDR response is initiated at temperatures well below the insulator-metal transition temperature where it is dominated by the temperature-dependent conductivity of the insulating phase. Finally, the dynamics of individual and coupled V3 O5 -based relaxation oscillators is reported, showing that capacitively coupled devices exhibit rich non-linear dynamics, including frequency and phase synchronization. These results establish V3 O5 as a new functional material for volatile threshold switching and advance the development of robust solid-state neurons for neuromorphic computing.

A first-principles study on transport properties of polyacene in zigzag graphene nanoribbon: Configuration, length and doping effects

Electronic transport properties of molecular junctions constructed by bridging a polyacene (PA) molecule between two zigzag graphene nanoribbons (ZGNR) are studied based on density functional theory and the nonequilibrium Green function method. It is found that the molecule-electrode coupling strength is related to the PA position with respect to the nanoribbon edge, which gives rise to the configuration dependency of transport properties. Negative differential resistance (NDR) is predicted in the junctions of which the PA molecule aligns with the inner part of the ZGNR. The on-set bias and current peak decrease as the PA molecule moves inward. The origin of NDR is presented by analyzing the transmission spectra, relative voltage-drop rate, and electron density difference of the junctions. The on-set bias is proportional to the energy of the resonance peak of the lowest unoccupied molecular orbital and can be tuned by the PA molecule length or by doping. This work provides a detailed discussion on PA-bridged ZGNR junctions, which may help to understand ZGNR-based molecular junctions and design negative differential resistance devices.

Origin of multi-level switching and telegraphic noise in organic nanocomposite memory devices.

The origin of negative differential resistance (NDR) and its derivative intermediate resistive states (IRSs) of nanocomposite memory systems have not been clearly analyzed for the past decade. To address this issue, we investigate the current fluctuations of organic nanocomposite memory devices with NDR and the IRSs under various temperature conditions. The 1/f noise scaling behaviors at various temperature conditions in the IRSs and telegraphic noise in NDR indicate the localized current pathways in the organic nanocomposite layers for each IRS. The clearly observed telegraphic noise with a long characteristic time in NDR at low temperature indicates that the localized current pathways for the IRSs are attributed to trapping/de-trapping at the deep trap levels in NDR. This study will be useful for the development and tuning of multi-bit storable organic nanocomposite memory device systems.

Research on the origin of negative effect in uniform doping GaN-based Gunn diode under THz frequency

The transport properties of GaN-based uniform doping Gunn diode are calculated by an ensemble Monte Carlo method. The drift velocity, electron density, and electric field distribution as a function of time in the device are illustrated under direct current (DC) and alternating current (AC) bias condition. With the help of port current, the relationship between electron transport status and port current can be acquired, which will be useful to understand the origin of negative differential resistance and guide the device design. Different from the traditional opinion, the maximum current do not appear at the same time when electron accumulation domain arrives at device anode. The reason is that when electron accumulation domain comes into heavily doped anode, the velocity will be decelerated a lot for highly ionized impurity scattering, and the electrons in the domain will be used to neutralize positive ion region which provides the electrons during formation of the domain. Some researchers believe that the electrons in the domain come from heavily doped cathode region, but our simulation shows clearly that the electrons come from heavily doped anode side. Finally, the AC simulation shows the possibility of negative differential resistance in GaN diode under THz frequency. What is more, AC simulation result has the same tendency with DC simulation.

First-principles study of high-field-related electronic behavior of group-III nitrides

Based on accurate band structures of AlN, GaN, and InN, we report physical quantities related to high-field electron transport, including effective masses, energies of inflection points, and satellite valleys in the conduction band. The band structures are obtained from density functional theory with a hybrid functional, as well as many-body perturbation theory based on the ${G}_{0}{W}_{0}$ approach. We also calculate the electron-energy relaxation time due to the electron-longitudinal-optical-phonon interaction within the Fr\ohlich model. Our results provide insights into the physical origin of negative differential resistance and the high-frequency characteristics of group-III nitrides and their alloys under high-field operation.

Negative differential resistance phenomena in colloidal quantum dots-based organic light-emitting diodes

The influence of ligands on the electrical behavior of CdSe/ZnS core-shell colloidal quantum dots (CQDs)-based organic light-emitting diodes is presented. Negative differential resistance (NDR) phenomena at room temperature are observed from single-layer device ITO/poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS)/CQDs/Al in which the original capping ligand tri-n-octylphosphine oxide (TOPO) of CQDs is exchanged with oleylamine, as well as in both bilayer device ITO/PEDOT:PSS/CQDs/BCP(10 nm)/Al and trilayer device ITO/PEDOT:PSS/CQDs/BCP(10 nm)/Alq3(10 nm)/Al. However, such a kind of NDR phenomenon disappears if TOPO is exchanged with hexadecylamine. Therefore, NDR phenomenon depends greatly on the ligands of the CQDs, and the origin of NDR from these devices is discussed.

Visualizing Atomic-Scale Negative Differential Resistance in Bilayer Graphene

We investigate the atomic-scale tunneling characteristics of bilayer graphene on silicon carbide using the scanning tunneling microscopy. The high-resolution tunneling spectroscopy reveals an unexpected negative differential resistance (NDR) at the Dirac energy, which spatially varies within the single unit cell of bilayer graphene. The origin of NDR is explained by two near-gap van Hove singularities emerging in the electronic spectrum of bilayer graphene under a transverse electric field, which are strongly localized on two sublattices in different layers. Furthermore, defects near the tunneling contact are found to strongly impact on NDR through the electron interference. Our result provides an atomic-level understanding of quantum tunneling in bilayer graphene, and constitutes a useful step towards graphene-based tunneling devices.

An &lt;i&gt;Ab Initio&lt;/i&gt; Study on Negative Differential Resistance in Pyrrole Trimer Molecular Device

The electronic transport properties of pyrrole trimer sandwiched between two electrodes are investigated by using nonequilibrium Green’s function formalism combined first-principles density functional theory. Theoretical results show that the system manifests negative differential resistance (NDR) behavior. A detailed analysis of the origin of negative differential resistance has been given by observing the shift in transmission resonance peak across the bias window with varying bias voltage.

Analysis of negative differential conductance of single-island single-electron transistors owing to Coulomb oscillations

Despite many years of effort, the precise origin of negative differential resistance (NDR) shown by some organic layers remains unclear. Tang et al. accounted qualitatively for NDR phenomena by coulomb blockade of single-electron transistors (SETs). From this foundation, a novel method based on analysis of the charge stability diagram of a SET is proposed in this study. The method can be used to systematically analyse negative differential conductance (NDC) characteristic of a SET and some organic layers. With this method, the NDC effect is explained with respect to device parameters, and several NDC cells proposed by others are analysed in detail. The results show that this method can be efficiently used to analyse the NDC effect of SETs and some organic layers.

Negative Differential Resistance in ZnO Nanowires Bridging Two Metallic Electrodes

The electrical transport through nanoscale contacts of ZnO nanowires bridging the interdigitated Au electrodes shows the negative differential resistance (NDR) effect. The NDR peaks strongly depend on the starting sweep voltage. The origin of NDR through nanoscale contacts between ZnO nanowires and metal electrodes is the electron charging and discharging of the parasitic capacitor due to the weak contact, rather than the conventional resonant tunneling mechanism.

Negative differential resistance in molecular junctions: Application to graphene ribbon junctions

Using self-consistent calculations based on nonequilibrium Green's function formalism, the origin of negative differential resistance (NDR) in molecular junctions and quantum wires is investigated. Coupling of the molecule to electrodes becomes asymmetric at high bias due to asymmetry between its highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels. This causes appearance of an asymmetric potential profile due to a depletion of charge and reduction of screening near the source electrode. With increasing bias, this sharp potential drop leads to an enhanced localization of the HOMO and LUMO states in different parts of the system. The reduction in overlap, caused by localization, results in a significant reduction in the transmission coefficient and current with increasing bias. An atomic chain connected to two graphene ribbons was investigated to illustrate these effects. For a chain substituting a molecule, an even-odd effect is also observed in the NDR characteristics.

Origin of Negative Differential Resistance in a Strongly Coupled Single Molecule-Metal Junction Device

A new mechanism is proposed to explain the origin of negative differential resistance (NDR) in a strongly coupled single molecule-metal junction. A first-principles quantum transport calculation in a Fe-terpyridine linker molecule sandwiched between a pair of gold electrodes is presented. Upon increasing the applied bias, it is found that a new phase in the broken symmetry wave function of the molecule emerges from the mixing of occupied and unoccupied molecular orbitals. As a consequence, a nonlinear change in the coupling between the molecule and the lead is evolved resulting in NDR. This model can be used to explain NDR in other classes of metal-molecule junction devices.

Origin of negative differential resistance and memory characteristics in organic devices based on tris(8-hydroxyquinoline) aluminum

Negative differential resistance (NDR) and memory phenomenon have been realized in current-voltage (I-V) characteristics of indium tin oxide/tris(8-hydroxyquinoline) aluminum/aluminum devices. The I-V curves have been divided into three operational regions that are associated with different working regimes of the devices: (i) bistable region, (ii) NDR region, and (iii) monotonic region. The bistable region disappeared after a couple of voltage sweeps from zero to a positive voltage. The bistable nature can be reinstated by applying a suitable negative voltage. The I-V characteristics have been explained in terms of space charge limited conduction. It has been found that injection of holes in these devices play an important role in NDR and resistive switching processes. Formation of nanofilamentary pathways and space charge field inhibition of injection elucidate the observed phenomenon well.

Ab Initio Density Functional Study on Negative Differential Resistance in a Fused Furan Trimer

We investigate the electronic transport properties of a trimer unit of cis-polyacetylene and a fused furan trimer using the ab initio density functional technique. Within the density functional theory, the effect of finite bias is introduced through nonequilibrium Green's functions. In the present study, both of the molecular systems have a thiol end group and they form a self-assembled monolayer on the Au (111) surface. The current−voltage characteristics of both the trimer unit of cis-polyacetylene and the fused furan trimer exhibit negative differential resistance over a certain range of bias voltage (±2.1 to ±2.45 V), and it is quite evident from the plot of differential conductance versus voltage. A detailed analysis of the origin of negative differential resistance has been given by observing the shift in transmission resonance peak across the bias window with varying bias voltage. The origin of the transmission resonance peak at certain bias voltages has been described from a study of molecular projected self-consistent Hamiltonian states.

Origin of negative differential resistance in molecular junctions of Rose Bengal

Negative differential resistance (NDR) is tuned at the junctions of electronically different dimers and trimers of Rose Bengal. Isolated molecule did not show any NDR. But it was induced to show double and triple NDRs with large peak to valley ratio (1.8–3.1) at 300K by varying number of neighbors and charging them by an electrical pulse. One could destroy or regenerate NDR by separating them or bringing together by a scanning tunneling microscope tip. NDR was also independent of polaronic nature. Bits 1 and 0 for cationic NDR (in dimer) and 0, 1, 2, and 3 for dianionic NDR (trimer) were written in an atomic scale junction. Importance of junction electronics and effective exposure is revealed.

Writing and erasing information in multilevel logic systems of a single molecule using scanning tunneling microscope

Large double negative differential resistance (NDR) has enabled a single quinone derivative to be stable in the neutral (0), singly reduced (1), typical neutral conformation generated by releasing the charge (2), and doubly reduced state (3) at 90K. The authors wrote and erased information by switching a single molecule among these four conducting states (0,1,2,3) showing random access memory and read only memory applications for terabit memory generation in future. Origin of NDR is investigated in typical functional groups of the molecule, in local environment, and at atomic junction with scanning-tunneling-microscope tip to conclude NDR as a collective phenomenon.

Changes of Coupling between the Electrodes and the Molecule under External Bias Bring Negative Differential Resistance

We report a first-principles study of electrical transport and negative differential resistance (NDR) in a single molecular conductor consisting of a borazine ring sandwiched between two Au(100) electrodes with a finite cross section. The projected density of states (PDOS) and transmission coefficients under various external voltage biases are analyzed, and it suggests that the variation of the coupling between the molecule and the electrodes with external bias leads to NDR. Therefore, we propose that one origin of NDR in molecular devices is caused by the characteristics of both the molecule and the electrodes as well as their cooperation, not necessarily only by the inherent properties of certain species of molecules themselves. The changes of charge state of the molecule have minor effects on NDR in this device because the Mulliken population analysis shows that electron occupation variation on the molecule is very small when different external biases are applied.

Physical origin of negative differential resistance in SOI transistors

From a two-dimensional solution of Laplace&apos;s equation it is shown that a significant increase in temperature occurs in the channel of SOI transistors due to the relatively poor thermal conductivity of the buried insulator. Based on this simulation an equation is derived which predicts that at small channel lengths the pinchoft point is shifted, an effect which is consistent with experimental observations. In addition, the positive &apos;kink&apos; is reduced with increasing gate voltage and this effect, together with the negative differential resistance, can be explained by a temperature increase in the channel.

Observation of electrical breakdown and negative resistance in an epitaxial GaAs film of a field effect structure

We have observed electrical breakdown and current-controlled negative differential resistance (NDR) in an epitaxial n-GaAs film at room temperature by using a field effect structure. The breakdown is attributed to the impact excitation of electrons trapped in 0.9-eV centers of concentration ∼1016 cm−3. The origin of NDR is explained by the theory which was originally developed for the breakdown phenomenon in Ge at low temperatures.