Negative Differential Resistance Devices Research Articles

High-performance GaAs/AlAs superlattice electronic devices in oscillators at frequencies 100–320 GHz

Negative differential resistance devices were fabricated from two epitaxial wafers with very similar GaAs/AlAs superlattices and evaluated in resonant-cap full-height waveguide cavities. These devices yielded output powers in the fundamental mode between 105 GHz and 175 GHz, with 14 mW generated at 127.1 GHz and 9.2 mW at 133.2 GHz. The output power of 4.2 mW recorded at 145.3 GHz constitutes a 50-fold improvement over previous results in the fundamental mode. The highest confirmed fundamental-mode oscillation frequency was 175.1 GHz. In a second-harmonic mode, the best devices yielded 0.92 mW at 249.6 GHz, 0.7 mW at 253.4 GHz, 0.61 mW at 272.0 GHz, and 0.54 mW at 280.7 GHz. These powers exceed those extracted previously from higher harmonic modes by orders of magnitude. The power of 0.92 mW constitutes an improvement by 77% around 250 GHz. The second-harmonic frequency of 317.4 GHz is the highest to date for superlattice electronic devices and shows an increase by 25% over previous results.

Designing Negative Differential Resistance Devices Based on Self‐Heating

AbstractThere are a number of important emerging applications that would benefit from simple circuit elements that exhibit tunable current‐controlled negative differential resistance (NDR). The advent of such devices would enable, for example, key components for threshold logic and neuromorphic computing such as threshold switches, periodic and chaotic oscillators, and small signal amplifiers. Circuit elements that provide NDR with modifiable electrical characteristics would also be useful for creating optimized “selectors” that enable addressing of individual memory cells in large resistance‐based memory arrays. Currently, there are no simple, bipolar, two‐terminal commercial devices that exhibit current‐controlled NDR. This paper demonstrates that current‐controlled NDR can, in principal, arise from any electrical conduction mechanism that depends superlinearly on temperature, and that in practice a broad spectrum of materials can be utilized to yield NDR. A model is presented that accurately predicts conditions under which NDR can be observed and guidelines are provided for choosing materials that result in desired electrical characteristics. This model accurately predicts the behavior of some existing structures and can be used to tailor future circuit elements for emerging applications. It may also explain the onset of a number of “soft breakdown” phenomena.

Recent progress in Van der Waals (vdW) heterojunction-based electronic and optoelectronic devices

The rediscovery of graphene in 2004 triggered an explosive expansion of research on various van der Waals (vdW) materials. The atomic layers of these vdW materials do not have surface crystal defects and are bonded by weak vdW interactions, thus the vdW materials can be stacked onto each other to form vdW heterojunction structures without needing to consider the lattice mismatch issue. In addition, the broad library of vdW materials makes it possible to design diverse types of heterojunctions with a wide range of band alignments, bandgaps, and electron affinities. Vertical vdW heterostructures especially offer numerous possibilities for the realization of high-performance electronic and optoelectronic devices. Therefore, these vdW heterostructures have received significant attention, and extensive relevant experimental results have been reported in the past few years. In this review, we first introduce the transfer techniques to form vdW heterojunction structures. Next, we discuss recent progress in vdW heterostructure-based electronic and optoelectronic devices, including vertical field effect transistors, negative differential resistance devices, memories, photodetectors, photovoltaic devices, and light-emitting diodes. Finally, we conclude this review by discussing the current challenges facing vdW heterojunction structure-based devices and our perspective on future research directions.

Negative differential resistance and rectification effects in zigzag graphene nanoribbon heterojunctions: Induced by edge oxidation and symmetry concept

By applying non-equilibrium Green's functions (NEGF) in combination with tight-binding (TB) model, we investigate and compare the electronic transport properties of H-terminated zigzag graphene nanoribbon (H/ZGNR) and O-terminated ZGNR/H-terminated ZGNR (O/ZGNR–H/ZGNR) heterostructure under finite bias. Moreover, the effect of width and symmetry on the electronic transport properties of both models is also considered. The results reveal that asymmetric H/ZGNRs have linear I–V characteristics in whole bias range, but symmetric H-ZGNRs show negative differential resistance (NDR) behavior which is inversely proportional to the width of the H/ZGNR. It is also shown that the I–V characteristic of O/ZGNR–H/ZGNR heterostructure shows a rectification effect, whether the geometrical structure is symmetric or asymmetric. The fewer the number of zigzag chains, the bigger the rectification ratio. It should be mentioned that, the rectification ratios of symmetric heterostructures are much bigger than asymmetric one. Transmission spectrum, density of states (DOS), molecular projected self-consistent Hamiltonian (MPSH) and molecular eigenstates are analyzed subsequently to understand the electronic transport properties of these ZGNR devices. Our findings could be used in developing nanoscale rectifiers and NDR devices.

Interface Engineering for Controlling Device Properties of Organic Antiambipolar Transistors.

The main purpose of this study is to establish a guideline for controlling the device properties of organic antiambipolar transistors. Our key strategy is to use interface engineering to promote carrier injection at channel/electrode interfaces and carrier accumulation at a channel/dielectric interface. The effective use of carrier injection interlayers and an insulator layer with a high dielectric constant (high-k) enabled the fine tuning of device parameters and, in particular, the onset (Von) and offset (Voff) voltages. A well-matched combination of the interlayers and a high-k dielectric layer achieved a low peak voltage (0.25 V) and a narrow on-state bias range (2.2 V), indicating that organic antiambipolar transistors have high potential as negative differential resistance devices for multivalued logic circuits.

First-principles studies on electronic properties of Oligo-p-phenylene molecular device

The electronic properties of Oligo-p-phenylene molecular device are studied through density functional theory (DFT) in combination with non-equilibrium Green's function (NEGF). The electronic transport properties of Oligo-p-phenylene molecular device are investigated in terms of I-V characteristics, transmission spectrum and total density of states (TDOS). The TDOS gets modified with the number of phenyl units present in the device and also the applied bias voltage influence Oligo-p-phenylene molecular device. The density of charge along Oligo-p-phenylene molecular device is observed in both the conduction band and in the valence band upon increasing bias voltage. The transmission spectrum of Oligo-p-phenylene molecular device provides the insights on the transition of electrons across various energy intervals. The results of the present work clearly show that Oligo-p-phenylene molecular device can be utilized as negative differential resistance (NDR) device and its NDR property can be fine-tuned with the bias voltage and also by the number of phenyl units.

A Resonant Tunneling Nanowire Field Effect Transistor with Physical Contractions: A Negative Differential Resistance Device for Low Power Very Large Scale Integration Applications

In this paper, the influence of ultra-scaled physical symmetrical contraction on electrical characteristics of ultra-thin silicon-on-insulator nanowires with circular gate-all-around structure is investigated by using a 3D Atlas numerical quantum simulator based on non-equilibrium green’s function formalism. It is demonstrated that local cross-section variation in a nanowire transistor results in the establishment of tunnel energy barriers at the source-channel and drain-channel junctions which change device physics and cause a transmission from a quantum wire (1-D) to a floating quantum dot nanowire (0-D) introducing a resonant tunneling nanowire FET (RT-NWFET) as an interesting concept of nanoscale MOSFETs. The barriers construct resonance energy levels in the channel region of nanowires because of the longitudinal confinement in three directions causing some fluctuation in I D–V GS characteristic. In addition, these barriers remarkably improve the subthreshold swing and minimize the ON/OFF-current ratio degradation at a low operation voltage of 0.5 V. As a result, RT-NWFETs are intrinsically preserved from drain–source tunneling and are an interesting candidate for developing the roadmap below 10 nm.

Pyridine “alligator-clip” as molecular negative differential resistor predicted by first-principles study

Based on non-equilibrium Green's function and density functional theory, a first-principles study of the transport properties of two benzene-pyridines sandwiching the σ barrier of ethyl is performed. Using symmetric leads, strong negative differential resistance (NDR) effects with high peak-to-valley ratios (PVRs) are present under low bias. When using asymmetric leads, the PVR can be modulated to higher value with the unchanging of voltage (Vpeak) corresponding current peak (Ipeak). Our investigations indicate that pyridine “alligator-clip” can be used as very good low bias molecular NDR devices.

An Unusual Mechanism for Negative Differential Resistance in Ferroelectric Nanocapacitors: Polarization Switching-Induced Charge Injection Followed by Charge Trapping.

Negative differential resistance (NDR) has been extensively investigated for its wide device applications. However, a major barrier ahead is the low reliability. To address the reliability issues, we consider ferroelectrics and propose an alternative mechanism for realizing the NDR with deterministic current peak positions, in which the NDR results from the polarization switching-induced charge injection and subsequent charge trapping at the metal/ferroelectric interface. In this work, ferroelectric Au/BiFe0.6Ga0.4O3 (BFGO)/Ca0.96Ce0.04MnO3 (CCMO) nanocapacitors are prepared, and their ferroelectricity and NDR behaviors are studied concurrently. It is observed that the NDR current peaks are located at the vicinity of coercive voltages (Vc) of the ferroelectric nanocapacitors, thus evidencing the proposed mechanism. In addition, the NDR effect is reproducible and robust with good endurance and long retention time. This study therefore demonstrates a ferroelectric-based NDR device, which may facilitate the development of highly reliable NDR devices.

Electronic and Optoelectronic Devices based on Two‐Dimensional Materials: From Fabrication to Application

Since the rediscovery of graphene in 2004, this material has attracted an enormous amount of interest owing to its unique structural, mechanical, electronic, and optical properties. Beyond this, the unique properties of graphene have also triggered extensive research on other two‐dimensional (2D) materials including transition metal dichalcogenides (TMDs), particularly for electronic and optoelectronic device applications. In particular, not only single junction but also various heterojunction devices based on 2D materials have afforded novel functionality and advances in many research fields. The availability of various 2D materials could allow the formation of a wide variety of heterojunctions with desired band alignments, thereby providing a powerful fabrication process platform for high‐performance electronic and optoelectronic devices. In this review, the important fabrication techniques of i) doping, ii) contact engineering, and iii) heterojunction formation for improving the performance of 2D‐material‐based devices are first introduced. Promising 2D‐material‐based electronic and optoelectronic devices are then discussed, including lateral/vertical field‐effect transistors (FETs), negative differential resistance (NDR) devices, memory, photodetectors, photovoltaics, and light‐emitting diode (LED) devices.

Negative Differential Resistance Device from Organic/Inorganic Hybrid Nanostructures.

Negative differential resistance device (NDR) fabricated by spin coating of organic/inorganic hybrid nanostructures at room temperature, is reported in the present paper. The coated organic layer is MEH-PPV (poly-[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylenevinylene] and inorganic layer is ZnO nanoparticles. The device shows negative differential resistance at low voltage and I–V characteristics of the device show multiple peaks at low voltage values. A value of 13 and 4 for the peak- to-valley ratio of current are reported in bi-layer and single layer structures respectively. Depending on the observed NDR signature, operating mechanisms are explored based on carrier (resonant) tunneling process and donor like trap mechanisms. This results show that the MEH-PPV/ZnO thin films gives good performance and is relevant for applications in optoelectronic devices such as a negative differential resistance.

Computational exploration and design of nano scale sensors and devices

We describe large-scale ab initio simulations of nanoscale sensors and transistors, which can predict the best-performing structures. In the sensors part we focus on mechanisms of detection of small molecules: ammonia, nitrogen dioxide, glucose and ethylene by nanotube-based sensors, and on a novel nano circuit involving a nanotube functionalized with a fragment of polymerase I enzyme. The nano circuit monitors replication of a single-stranded DNA and can potentially be used to sequence DNA by detecting electrical signatures of the adding bases. We discuss modifications that should enable reliable distinction between some of the bases, and our work towards complete sequencing. We also describe computational optimization of graphene nanoribbon (GNR) structures and devices, including the determination of atomically precise polymer-GNR conversion mechanism due hole injection, the design of realistic, experimentally realizable negative differential resistance device based on 7-GNR, and optimization of transistor structures consisting of a GNR channel, BN insulating layers and an Al gate.

Phosphorene/rhenium disulfide heterojunction-based negative differential resistance device for multi-valued logic.

Recently, negative differential resistance devices have attracted considerable attention due to their folded current–voltage characteristic, which presents multiple threshold voltage values. Because of this remarkable property, studies associated with the negative differential resistance devices have been explored for realizing multi-valued logic applications. Here we demonstrate a negative differential resistance device based on a phosphorene/rhenium disulfide (BP/ReS2) heterojunction that is formed by type-III broken-gap band alignment, showing high peak-to-valley current ratio values of 4.2 and 6.9 at room temperature and 180 K, respectively. Also, the carrier transport mechanism of the BP/ReS2 negative differential resistance device is investigated in detail by analysing the tunnelling and diffusion currents at various temperatures with the proposed analytic negative differential resistance device model. Finally, we demonstrate a ternary inverter as a multi-valued logic application. This study of a two-dimensional material heterojunction is a step forward toward future multi-valued logic device research.

Negative differential resistance effect in similar right triangle graphene devices

In this work, nanojunctions consisting of two combined similar right triangle graphenes (SRTGs) bonded covalently with zigzag-edged graphene nanoribbon electrodes are designed, and their electron transport properties are investigated using density functional theory and non-equilibrium Green's function method. Results reveal that the SRTG-based devices exhibit an interesting negative differential resistance (NDR) effect and present a rule indicating that the NDR effect increases with the increasing sizes of both SRTGs. The electron transport properties are further tested using two combined SRTGs with different sizes. Overall, this study suggests that the SRTG-based structures are promising candidates in the design of nanoscale NDR devices.

Strong n-type molecule as low bias negative differential resistance device predicted by first-principles study

A first-principles study of the transport properties of two thiolated pentacenes sandwiching ethyl is performed. The thiolated pentacene molecule shows strong n-type characteristics when contact Ag lead because of low work function about metal Ag. A strong negative differential resistance (NDR) effect with large peak-to-valley ratio of 758% is present under low bias. Our investigations indicate that strong n- or p-type molecules can be used as low bias molecular NDR devices and that the molecular NDR effect based on molecular-level leaving not on molecular-level crossing has no hysteresis.

Multiple Negative Differential Resistance Device by Using the Ambipolar Behavior of Tunneling Field Effect Transistor with Fast Switching Characteristics.

We propose a novel double-peak negative differential resistance (NDR) characteristic at the conventional single-peak MOS-NDR circuit by employing ambipolar behavior of TFET. The fluctuated voltage transfer curve (VTC) from ambipolar inverter is analyzed with simple model and successfully demonstrated with TFET, as a practical example, on the device simulation. We also verified that the fluctuated VTC generates additional peak and valleys on NDR characteristics by using circuit simulations. Moreover, by adjusting the threshold voltage of conventional MOSFET, ultra-high 1st and 2nd peak-to-valley current ratio (PVCR) over 10(7) is obtained with fully suppressed valley currents. The proposed double-peak NDR circuit expected to apply on faster switching and low power multi-functional applications.

Tuning electronic transport of zigzag graphene nanoribbons by ordered B or N atom doping

Calculations of electronic structures and transport properties of zigzag graphene nanoribbons (ZGNRs) by ordered doping of a column of boron (B) or nitrogen (N) atoms were conducted using density functional theory combined with the non-equilibrium Green's function. Introducing B or N impurity atoms into ZGNRs with an odd number of zigzag chains can suppress currents compared with the intrinsic ZGNR device. The ZGNRs with an even number of zigzag chains across their width show that B or N atom doping can increase currents compared with the intrinsic ZGNR nanojunction. Notably, B or N doping can induce a significant negative differential resistance behavior for ZGNRs with an even number of zigzag chains across their width. These findings provide avenues to modify the electronic transport of ZGNR-based systems. The findings also suggest that ZGNRs are potential materials for future nanoscale negative differential resistance device.

Novel five-state latch using double-peak negative differential resistance and standard ternary inverter

We propose complement double-peak negative differential resistance (NDR) devices with ultrahigh peak-to-valley current ratio (PVCR) over 106 by combining tunnel diode with conventional CMOS and its compact five-state latch circuit by introducing standard ternary inverter (STI). At the “high”-state of STI, n-type NDR device (tunnel diode with nMOS) has 1st NDR characteristics with 1st peak and valley by band-to-band tunneling (BTBT) and trap-assisted tunneling (TAT), whereas p-type NDR device (tunnel diode with pMOS) has second NDR characteristics from the suppression of diode current by off-state MOSFET. The “intermediate”-state of STI permits double-peak NDR device to operate five-state latch with only four transistors, which has 33% area reduction compared with that of binary inverter and 57% bit-density reduction compared with binary latch.

Design of Broadband Non-Foster Circuits Based on Resonant Tunneling Diodes

A non-Foster circuit (NFC) based on the resonant tunneling diode (RTD) is proposed for application to broadband impedance matching of electrically small antennas (ESAs). NFCs have traditionally been implemented with transistor pairs to achieve negative impedance, but these have limitations with respect to performance and operational bandwidth at high frequencies. At certain biasing voltages, double-barrier RTDs behave as negative differential resistance (NDR) devices, which may be transformed to exhibit negative impedance. In contrast to the transistor-based NFC, these structures serve to gyrate or invert the load impedance, such that an inductive load will lead to a negative capacitance, and vice versa. This device is termed a negative impedance inverter (NII). We demonstrate negative impedance behavior for prototypes with measurements of negative resistance at up to 3 GHz, and device gain of around 5 dB from dc to 4 GHz. Design for stability of the RTD is performed using the Nyquist stability criterion. Stabilized negative capacitance NFCs show optimum performance from dc to the GHz range depending upon the load value. These NFCs are used to impedance match an antenna at low frequencies. An antenna with only one resonance at 3.5 GHz has been transformed with two different matching circuits: to an antenna encompassing the 1–2-GHz range, as well as the VHF/UHF bands from 300 MHz to 1 GHz. Additionally, RTDs have been demonstrated for operation at up to THz frequencies, so this topology can be extended to higher frequencies subject to fabrication constraints.

Negative differential resistance in GeSi core-shell transport junctions: the role of local sp(2) hybridization.

We report a theoretical investigation of nonlinear quantum transport properties of Au/GeSi/Au junctions. For GeSi semiconducting core-shell structures brought into contact with Au electrodes, a very unusual behavior is that the tunneling transport is on-resonance right at equilibrium. This resonance is not due to the alignment of a quantum level in GeSi to the electrochemical potential of Au, but due to the alignment of very sharp DOS features - hot spots, localized at the two Au/GeSi interfaces of the device. An applied bias voltage shifts the hot spots relative to each other which gives rise to substantial negative differential resistance (NDR). The hot spots localized at the two interfaces were found to be due to the unbonded pz orbital of a sp(2) hybridized interface Si atom which is surrounded by three non-sp(2) hybridized neighbors. The mechanism of inducing hot spots and NDR by a local structure unit is not limited to the GeSi. The results suggest an interesting scheme for constructing NDR devices by orbital manipulation, to be more explicit, for example, by designing local structural units having unbonded orbitals at the interfaces between electrodes and the central region of the transport junction.