Observation Of Negative Differential Resistance Research Articles

22‐3: Negative Capacitance ZAO/ZnO Ferroelectric Thin‐Film Transistor for Neuromorphic Computing

We report complementary metal‐oxide semiconductor (CMOS)‐compatible, negative capacitance (NC) ferroelectric (FE) zirconium‐aluminum oxide (ZAO)/ZnO thin‐film transistors (TFTs) at a low thermal budget of 360 °C. The NC‐FE‐TFTs demonstrate uniform device‐to‐device performances, featuring a high memory window of 6.7 ± 0.1 V and steep subthreshold swing of 43 ± 4 mV dec–1 . The observation of negative differential resistance at room temperature confirms the NC effect in FE‐ZAO/ZnO TFTs. In addition, a learning accuracy of ≈92% is achieved, highlighting the potential for high precision neuromorphic computing application.

Density functional theory study of the electronic and optical properties of pentagraphyne nanotubes.

Pentagraphyne (PG-yne), a recently predicted two-dimensional (2D) carbon allotrope with appealing properties, has opened up possibilities for a wide range of applications. In this study, we investigate the structural, electronic, optical, and electrical transport properties of a novel one-dimensional (1D) system called pentagraphyne nanotubes (PG-yneNTs), formed by rolling a PG-yne sheet, using density functional theory (DFT) calculations. We design PG-yneNTs with diameters ranging from 6.94 Å to 13.62 Å and employ state-of-the-art theoretical calculations to confirm their energetic, dynamic, and thermodynamic stability. Our electronic band structure calculations reveal that all these nanotubes are wide indirect band gap semiconductors. Remarkably, PG-yneNTs exhibit superior optical properties, including high absorption coefficients and absorption spectra covering the visible regime of the electromagnetic spectrum, making them potential candidates for visible-light-driven photocatalysis and solar cells. Interestingly, both the electronic and optical band gaps increase with the diameter of the nanotubes. Additionally, the observation of negative differential resistance (NDR) phenomena in (4, 0) PG-yneNT suggests their potential applications in NDR devices such as fast switches, frequency multipliers, and memory devices.

Observation of negative differential Resistance(NDR) in chemically synthesized CuGaSe2 nanorods

CuGaSe2 nanorods has been synthesized through chemical bath deposition method using PVP(polyvinylpyrrolidone) as capping agent. Formation of CuGaSe2 nanorods was confirmed by SEM and TEM analysis. A systematic electrical study has been done on CuGaSe2 nanostructure by changing the Cu to Ga(%) composition ratio from CuSe2 to GaSe nanostructure. I-V characteristics showed that CuGaSe2 nanorods exhibit a negative differential resistance(NDR) region and their peak/valley ratio increases with Ga(%) composition. The occurrence of the NDR region is due to the electron tunneling through the potential barrier of Cu/CuGaSe2 interface. The increase in peak current in NDR region in CuGaSe2 nanorods with the increase in Ga(%) makes them suitable application in building oscillator and memory devices.

Observation of negative differential resistance in SiO2/Si heterostructures

The negative differential resistance (NDR) effect been widely reported in the physical systems of traditional semiconductors, and corresponding theoretical mechanisms are known and applied. However, exploring the origin of NDR phenomena emerging in new structures or conditions remains a worthwhile challenge. Here, we report an experimental observation of an NDR effect based on SiO 2 /Si heterojunctions by injecting photo-generated carriers via vacuum ultraviolet (VUV) irradiation. We propose a complex competition mechanism between trap centers’ and recombination centers’ dominating carrier transport behavior. This is caused by the difference in spatial distribution of density of band-tail states and defect states in SiO 2 /Si. This work may inspire further consideration of SiO 2 /Si heterojunctions for electronic applications. • NDR effect is observed in SiO 2 /Si heterojunction via vacuum VUV irradiation • NDR effect originates from difference in spatial distribution of density of states • SiO 2 /Si heterojunction with NDR effect shows potential for space applications Using vacuum ultraviolet irradiation, Jia et al. observe a negative differential resistance effect in the structure of SiO2/Si heterojunction. This work may bring new opportunities for traditional SiO 2 /Si heterojunctions in electronic applications, such as switches and amplifying elements in space detection systems.

Direct observation of negative differential resistance in WS2 homojunction

Vertical tunneling junctions showing negative differential resistance (NDR) are realized in WS2 homojunction devices. Mono-/multilayered single crystalline WS2 is grown using chemical vapor deposition. NDR is observed through resonant tunneling in Au/bi-layer WS2/Au and Pt/few-layered WS2/Au tunneling junctions by back-gating at room temperature. While two-dimensional materials have been a central focus of materials research during the past decade, exploiting novel properties in diverse layers of these materials is emerging with new designs for electronic devices. Our results pave the way for novel resonant tunneling devices presenting a route to fabricate homojunction WS2 with simple fabrication techniques.

Observation of resistance switching in Vanadyl-phthalocyanine thin films

Herein, we report the first observation of Negative differential resistance (NDR) associated with resistance switching in Vanadyl-phthalocyanine (VOPc) based devices with the configuration: ITO/F4TCNQ/VOPc/MoO3/Al. It was observed that the devices were initially at low resistance ON state (LS) and were switched to high resistance OFF state (HS) at sufficient applied bias. The NDR behaviour was observed during the initial sweep for each device (often referred to as the writing process). The ON/OFF state transition was attributed to the formation and neutralization of interface dipoles at the ITO/VOPc interface. Finally, the observed non-volatile RS switching behaviour was demonstrated employing impedance spectroscopic studies. This study opens up the potential applications of VOPc Resistance Switching devices in security and data protection applications.

Observation of negative differential resistance in mesoscopic graphene oxide devices

The fractions of various functional groups in graphene oxide (GO) are directly related to its electrical and chemical properties and can be controlled by various reduction methods like thermal, chemical and optical. However, a method with sufficient controllability to regulate the reduction process has been missing. In this work, a hybrid method of thermal and joule heating processes is demonstrated where a progressive control of the ratio of various functional groups can be achieved in a localized area. With this precise control of carbon-oxygen ratio, negative differential resistance (NDR) is observed in the current-voltage characteristics of a two-terminal device in the ambient environment due to charge-activated electrochemical reactions at the GO surface. This experimental observation correlates with the optical and chemical characterizations. This NDR behavior offers new opportunities for the fabrication and application of such novel electronic devices in a wide range of devices applications including switches and oscillators.

Atomically manufactured nickel\u2013silicon quantum dots displaying robust resonant tunneling and negative differential resistance

Providing a spin-free host material in the development of quantum information technology has made silicon a very interesting and desirable material for qubit design. Much of the work and experimental progress has focused on isolated phosphorous atoms. In this article, we report on the exploration of Ni–Si clusters that are atomically manufactured via self-assembly from the bottom-up and behave as isolated quantum dots. These small quantum dot structures are probed at the atomic-scale with scanning tunneling microscopy and spectroscopy, revealing robust resonance through discrete quantized energy levels within the Ni–Si clusters. The resonance energy is reproducible and the peak spacing of the quantum dot structures increases as the number of atoms in the cluster decrease. Probing these quantum dot structures on degenerately doped silicon results in the observation of negative differential resistance in both I–V and dI/dV spectra. At higher surface coverage of nickel, a well-known √19 surface modification is observed and is essentially a tightly packed array of the clusters. Spatial conductance maps reveal variations in the local density of states that suggest the clusters are influencing the electronic properties of their neighbors. All of these results are extremely encouraging towards the utilization of metal modified silicon surfaces to advance or complement existing quantum information technology.

Films fabricated from partially fluorinated graphene suspension: structural, electronic properties and negative differential resistance

The band structure and electric properties of films created from a partially fluorinated graphene suspension are analyzed in this paper. As may be inferred from the structural study, graphene islands (quantum dots) are formed in these films. Various types of negative differential resistance (NDR) and a step-like increase in the current are found for films created from the fluorinated graphene suspension. NDR resulting from the formation of the potential barrier system in the film and corresponding to the theoretical prediction is observed for a relatively low fluorination degree. The origin of the NDR varies with an increase in the fluorination degree of the suspension. The observation of NDR in the fluorinated films widens the range of application of such films, including as active device layers fabricated using 2D printed technologies on rigid and flexible substrates.

Observation of negative differential resistance in GaN-based multiple-quantum-well light-emitting diodes

Anomalous current–voltage behaviors, such as negative differential resistance (NDR) and current hysteresis, are observed in the room-temperature current–voltage (I-V) curves of InGaN/GaN multiple-quantum-well light-emitting diodes. It is found that the NDR can be observed in the positive voltage range of the I-V curve only when the samples are pretreated with a negative voltage before sweeping, and the NDR disappears permanently after an over-current treatment. The dependence of the NDR upon the negative voltage and sweeping conditions leads to the conclusion that a variation of the charging state of the defect-induced hole traps is responsible for the anomalous I-V behaviors. Therefore, NDR is excluded as a feature of the tunneling transport mechanism, especially in GaN-based devices with a high defect density.

Observation of room temperature negative differential resistance in solution synthesized ZnO nanorod

We report the observation of negative differential resistance (NDR) in solution synthesized ZnO nanorod. The ZnO nanorod was fabricated as a two terminal planar device using lithographically patterned Au electrodes. The measured current–voltage response of the device has shown a negative differential resistance behavior. The peak-to-valley current ratio of the NDR is found to be greater than 4. The mechanism of this observed NDR effect has been explained based on charge trapping and de-trapping at the nanoscale contacts. It is the first observation of negative differential resistance effect in solution synthesized ZnO nanorod.

Observation of negative differential resistance and electrical bi-stability in chemically synthesized ZnO nanorods

Zinc oxide nanorods/p-Si heterostructures have been fabricated by depositing the chemically synthesized ZnO nanorods on p-type silicon substrate. Heterostructure shows electrical bi-stability and negative differential resistance (NDR) only at the beginning of the forward bias region, and these phenomena have been explained with the help of energy band diagram. An explanation is proposed for the origin of electrical bi-stability in light of the electric field induced charge transfer across the junction, and the NDR phenomena could be attributed to interfacial traps and defect level that arises due to oxygen and zinc interstitial vacancies. Room temperature photoluminescence measurement of ZnO nanorods exhibits the emission peaks at about 466 nm and 566 nm which are attributed to oxygen vacancies and Zn interstitials. A correlation between NDR and blue emission phenomena in the ZnO nanorods due to defects states has been established.

Space-charge limited current in the series resistance of GaAs solar cells

We report the observation of space-charge limited current in the current–voltage characteristics of GaAs solar cells as evidenced by an abrupt decrease in the series resistance, a concurrent steep increase in the dark current at a threshold voltage and the observation of a quadratic dependence of the dark current on the voltage across the series resistance above threshold. The abrupt decrease in the series resistance at threshold, results in the observation of negative differential resistance and a subsequent hysteresis in the current–voltage characteristics. Auger electron spectroscopy analysis shows that the space-charge limited current can be attributed to a thin insulating CrAs layer at the contact/semiconductor interface.

The Effect of Germanium Fraction on High-Field Band-to-Band Tunneling in ${\rm p}^{+}$-SiGe/${\rm n}^{+}$-SiGe Junctions in Forward and Reverse Biases

The dependence of band-to-band tunneling in <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm p}^{+}\hbox{-}{\rm Si}_{1-x}{\rm Ge}_{x}/{\rm n}^{+}\hbox{-}{\rm Si}_{1-x}{\rm Ge}_{x}$</tex></formula> homojunctions on Ge fraction and electric field is investigated in the range <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$2\hbox{--}3\times 10^{8}~{\rm V}/{\rm m}$</tex></formula> . Negative differential resistance (NDR) in forward bias is observed for each device with the highest peak tunneling-current density of 8.2 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm kA}/{\rm cm}^{2}$</tex></formula> without any postannealing step. Reverse-biased band-to-band tunneling, as relevant for tunneling field-effect transistors, is also measured. Tunneling via junction defects can mask band-to-band tunneling and the observation of NDR at forward bias confirms negligible tunneling via those defects. Both forward-biased and reverse-biased data are compared with models versus electric field and Ge fraction.

Observation of Negative Differential Resistance in a GaN/AlGaN/GaN: Possible Tunneling Junction Using Polarization

We report an anomalous current–voltage behavior in an n-type GaN/undoped InGaN/undoped GaN/undoped AlGaN/n-type GaN diode grown by metalorganic chemical vapor deposition. The tunneling-junction-like band profile of the undoped GaN/undoped AlGaN/n-type GaN (GAG) structure is formed by a spontaneous and piezo polarization effect. We observe negative-differential resistance (NDR) behavior in the diode with the GAG structure. The NDR behavior suggests a possible tunneling junction consisting in the GAG structure.

Negative differential resistance in electron tunneling in ultrathin films near the two-dimensional limit

We report on our observation of negative differential resistance (NDR) in electron tunneling conductance in atomic-scale ultrathin Ag films on Si(111) substrates. NDR was observed by scanning tunneling spectroscopy measurements. The tunneling conductance depends on the electronic local density of states (LDOS) of the sample. We show that the sample bias voltage, at which negative differential resistance and peak negative conductance occur, depends on the film thickness. This can be understood from the variation in the LDOS of the Ag films as a function of film thickness down to the two-dimensional limit of one atomic layer. First principles density functional theory calculations have been used to explain the results.

InAs/AlGaSb heterojunction tunnel field‐effect transistor with tunnelling in‐line with the gate field

AbstractThe first fabrication of a III‐V tunnel field‐effect transistor (TFET) with tunneling directed perpendicular to the gate is reported. This new transistor geometry utilizes an InAs/Al0.45Ga0.55Sb staggered‐gap tunnel junction intended for high on current and steep subthreshold swing. The first measurements of the transistor transport properties at room temperature and ‐50 °C are provided. Tunneling transport is confirmed by the observation of negative differential resistance in the tunnel junction in the forward bias polarity. Transistor on‐current of 21 μA/μm at 0.3 V and subthreshold swing of 830 mV/decade is found. The large subthreshold swing is consistent with the large density of interface traps at the oxide/semiconductor interface (© 2012 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Observation of negative differential resistance in diketopyrrolopyrrole-based copolymer films

Remarkable and repeatable negative differential resistance (NDR) phenomenon was observed in a metal-polymer-metal structure diode based on bishexyloxy-divinyl-benzene-alt-diketopyrrolopyrrole (C6DPPPPV), a type of donor-acceptor (D-A) conjugated copolymer. Thickness dependence of the devices implied that the observed NDR characteristics were bulk-controlled. The device performance was considered to depend on the slow trapping and releasing processes related to the local deep states, which was enhanced by the growth and thermal rupture of conducting filaments through the organic layer. The results suggest that the D-A conjugated copolymer is a promising memory material based on NDR effect.

Observation of negative differential resistance in DNA molecular junctions

The mechanically controllable break junction technique is used to study charge transport through suspended DNA molecules. The current-voltage (I-V) characteristics in an aqueous solution display series of negative differential resistance (NDR) and hysteresis behavior. Under high-vacuum conditions, the peak positions of NDR shift to lower voltage, and the amplitude is reduced dramatically. The observed NDR behavior is consistent with the polarization mechanism in DNA molecular junctions, which demonstrates a change in the coupling of the molecular level to a polaron mode under different environment.

Observation of negative differential resistance from a Schottky-barrier structure embedded with Fe quantum dots

A Au/ZnS/Fe-quantum dots (QDs)/ZnS/n +-GaAs(1 0 0) Schottky-barrier structure containing five layers of spherical Fe QDs with diameter around 3 nm was fabricated by the molecular beam epitaxy technique. Its current–voltage ( I– V) characteristics measured from 5 to 295 K display negative differential resistance (NDR) for temperature ⩽50 K, which is caused by the presence of Fe QDs. The highest peak-to-valley current ratio obtained at 5 K is as high as 15:1. Staircase-like I– V characteristic was also observed at low temperature in some devices fabricated from this structure. Possible mechanisms that can account for the observed unusual I– V characteristics in this structure were discussed.