High Peak-to-valley Current Ratio Research Articles

Charge transfer mechanism for realization of double negative differential transconductance

With development of information age, multi-valued logic (MVL) technology utilizing negative differential transconductance (NDT) phenomenon has drawn attention as next-generation computing technology that can replace binary logic. However, because conventional NDT devices primarily use ternary logic, multiple-peak NDT device is required for higher-radix MVL that can process more datasets. Here, van der Waals double-peak anti-ambipolar transistor (AAT) as NDT device was developed by utilizing peak voltage (Vpeak) modulation of NDT peak. For realization of quaternary logic, Vpeak modulation technology was developed through charge transfer mechanism from channel, thereby shifting NDT peak and increasing peak-to-valley current ratio (PVCR). Furthermore, Double-peak AAT was implemented through parallel configuration of two AATs with different Vpeak values. Finally, quaternary inverter with four widely stable logic states was implemented by utilizing the developed double-peak AAT with two distinct NDT peaks and high PVCR. This double-peak AAT is expected to contribute to the development of next-generation MVL technology capable of processing datasets.

Record peak current density of over 1500 kA/cm2 in highly scaled AlN/GaN double-barrier resonant tunneling diodes on free-standing GaN substrates

This work demonstrates high-performance AlN/GaN double-barrier resonant tunneling diodes (RTDs) with high peak current density grown by plasma-assisted molecular beam epitaxy on c-plane free-standing GaN substrates, featuring stable and repeatable negative differential resistance (NDR) characteristics at room temperature. By scaling down the barrier thickness of AlN barrier and the lateral mesa size of collector, the record peak current density of 1551 kA/cm2 is achieved along with a peak-to-valley current ratio (PVCR) of 1.24, which is attributed to the reduced resonant tunneling time under thinner AlN barrier and the suppressed external incoherent valley current by reducing the dislocation number contained in the RTD device with the smaller size of collector. By statistically analyzing the NDR performance of RTD devices with different thicknesses of AlN barrier, the average peak current density increases from 145.7 to 1215.1 kA/cm2, while the average PVCR decreases from 1.45 to 1.1, correspondingly, accompanying with a decreased peak voltage from 6.89 to 5.49 V, with downscaling the AlN barrier thickness from 1.5 to 1.25 nm. The peak current density obtained in this work is the highest value among all the reported nitride-based RTDs up until now while maintaining high PVCR value simultaneously, which illustrates that ultra-scaled RTD based on vertical quantum-well structure and lateral collector size is a valuable approach for the development of nitride-based RTDs with excellent NDR characteristics and reveals their great potential applications in high-frequency oscillation sources and high-speed switch circuits.

Hydrogenated cove-edge aluminum nitride nanoribbons for ultrascaled resonant tunneling diode applications: a computational DFT study

While synthesizing quasi-one-dimensional nanoribbons, there is a finite probability that edges have cove-edge defects. This paper focuses on the structural, electronic, and transport properties of cove-edge aluminum nitride nanoribbons (AlNNR) using density functional theory and the non-equilibrium Green’s function (NEGF) method. The cove-edge AlNNRs are thermodynamically stable and exhibit metallic behavior. Interestingly, the calculated current–voltage characteristics of the cove-edge AlNNR-based nanodevices show negative differential resistance (NDR). The H-AlN-Cove nanodevice exhibits high peak-to-valley current ratio (PVCR) of the order of 107. The calculated PVCR of the H-AlN-Cove nanodevice is 106 times higher than that of the silicene nanoribbon (SiNR) and graphene nanoribbon (GNR), and 104 times higher than that of the phosphorene nanoribbon (PNR) and arsenene nanoribbons (ANR)-based devices respectively. The NDR feature with high PVCR provides a prospect for the cove-edge AlNNR in nanodevice applications.

Bidirectional negative differential resistance in AlN/GaN resonant tunneling diodes grown on freestanding GaN

In this paper, we report bidirectional negative differential resistance (NDR) in Al(Ga)N/GaN/AlN resonant tunneling diodes grown on free-standing GaN substrates by RF-plasma assisted molecular beam epitaxy. Bidirectional NDR has exhibited a current–voltage (I–V) characteristic in both forward and reverse biases at room temperature. The positive peak current density is 160 kA/cm2 with a peak to valley current ratio (PVCR) of 1.34, and the negative peak current density is 112 kA/cm2 with a high PVCR of 1.56. The bidirectional NDR is attributed to the change in the polarization field in the active region, which is caused by the asymmetric barrier component.

Controlling Phase‐Coherent Electron Transport in III‐Nitrides: Toward Room Temperature Negative Differential Resistance in AlGaN/GaN Double Barrier Structures

AbstractResonant tunneling of electrons is important for the manufacture of high‐speed electronic oscillators and the electron injection control in quantum cascade lasers. In this work, room temperature negative differential resistance (NDR) in AlGaN/GaN double barrier structure with AlN/GaN digital alloy (DA) barriers is demonstrated. The peak‐to‐valley current ratio (PVCR) ranges from 1.1 to 1.24 at room temperature and becomes 1.5 to 2.96 at low temperatures, whereas no NDR is observed in double barrier structures with conventional ternary AlGaN barriers. The room temperature NDR together with the high PVCR at low temperature is attributed to the suppression of alloy disorder scattering by introducing AlN/GaN DA barriers. This work presents the successful control of phase‐coherent electron transport in III‐nitride heterostructures and is expected to benefit the future design of nitride‐based resonant tunneling structures and high‐speed electronic devices.

Superior Peak to Valley Current Ratio of the InAs/Gasb Core-Shell Nanowires for Tunnel Diode Application

Raising transistors density led by scaling is responsible for the increase of the power consumption. Consequently, the supply voltage scaling is a strong issue in recent years. Tunnel diode is considered as one of the potential candidate for low power applications. In this respect, the broken-gap InAs/GaSb heterostructure which has narrow bandgap and small effective mass that increase interband tunneling probability to use to fabricate the core-shell nanowires for low power tunnel diode application. Peak to valley current ratio (PVCR) of negative differential resistance is a property which occurs in tunnel diode to determine the amplification of an AC signal ability. We demonstrate an intensive negative differential resistance phenomenon and PVCR in InAs/GaSb core-shell nanowires device. The tunnel diode characteristics display a higher peak to valley current ratio of 8.69 at VDD= 0.32 V. Among all published literature, our result show a record high PVCR to the author’s best knowledges. InAs/GaSb core-shell nanowires are promising candidate for low power high switching speed application.

Tunnel Dielectric Field-Effect Transistors with High Peak-to-Valley Current Ratio

We present silicon-compatible tunnel dielectric field-effect transistors with strong negative differential resistance. On-state tunneling currents have been improved and fully suppressed ambipolarity with lowest subthreshold slope (SS) 10 mV/dec. In addition to the TFET mode, our device works as the negative transconductance characteristic that produces a high current peak-to-valley current ratio (PVR) (up to 107). Numerical simulations demonstrate the impact of tunnel dielectric layer thickness, gate oxide thickness and temperature on the PVR. With the significant improvement in SS, on-state current and high PVR, this tunnel dielectric transistor provides an effective technique for enhancing the drive current, and realizes its applications in logic and memory circuits.

High peak-to-valley current ratio In0.53Ga0.47As/AlAs resonant tunneling diode with a high doping emitter

An In0.53Ga0.47As/AlAs resonant tunneling diode (RTD) with a high doping emitter is designed and fabricated using air bridge technology. The RTD exhibits a high peak-to-valley current ratio (PVCR) of more than 40 at room temperature, with a peak current density of 24 kA/cm2. The extraction of device parameters from DC and microwave measurements is presented together with an RTD equivalent circuit. The high PVCR RTD with small intrinsic capacitance is favorable for microwave/THz applications.

To observe bidirectional negative differential resistance at room temperature by narrowing transport channels for charge carriers in vertical organic light-emitting transistor

Bidirectional negative differential resistance (NDR) at room temperature with high peak-to-valley current ratio (PVCR) of ∼10 are observed from vertical organic light-emitting transistor indium-tin oxide (ITO)/N,N′-di(naphthalene-1-yl)-N,N′-diphenyl-benzidine) (α-NPD)(60nm)/Al(30nm)/α-NPD(60nm)/tris-(8-hydroxyquinoline) aluminium (Alq3)(50nm)/Al by narrowing the transport channels for charge carriers with a thick-enough middle Al gate electrode layer to block charge carriers transporting from source electrode to drain electrode. When the transport channel for charge carriers gets large enough, the controllability of gate bias on the drain–source current gets weaker and the device almost works as an organic light-emitting diode only. Therefore, it provides a very simple way to produce NDR device with dominant bidirectional NDR and high PVCR (∼10) at room temperature by narrowing transport channels for charge carriers in optoelectronics.

High performance aluminum arsenic intraband resonant microwave devices

We report on GaAs/AlAs triple-barrier quantum well intraband (TBQWI) heterostructures grown by molecular beam epitaxy (MBE) on n + GaAs substrate. Heterostructure quality was evaluated by X-ray diffraction and photoluminescence spectrum measurements. The position of the broad peak near 65.84° corresponds well to the diffraction from the (4 0 0) face of AlAs layers assuming intensity of total AlAs spacers and barriers. The 10K photoluminescence (PL) data has a strong peak at 8140 Å. The PL spectrum is dominated by a sharp peak centered at the emission energy of 1.52 eV attributed to the energy of e1-hh bond exciton of GaAs layer. TBQWI heterostructures were grown and processed into resonant tunneling diode (RTD). Room temperature electrical measurement of the TBQWI RTD yielded maximum peak to valley current ratio (PVCR) of 120 with peak current density ( J p) of 2.1 kA/cm 2. The high PVCR of this GaAs/AlAs TBQWI RTD is, to the better of our knowledge, one of the higher PVCRs obtained in any intraband tunnel device.

Observation of room temperature negative differential resistance (NDR) in organic light-emitting diode with inorganic dopant

Room temperature negative differential resistance (NDR) current–voltage ( I– V) curves with high peak-to-valley (PTV) current ratio (>5) were observed first in organic light electroluminescence diodes (OLEDs). The OLED has the configuration of Al/Alq 3 (aluminum tris-(8-hydroxygninoline))/TPD ( N, N′-diphenyl- N, N′-bis(3-methylphenyl)-1,l′-bipheny-4,4′-diamine)/indium tin oxide (ITO) with TDP doped with iodine (I 2) or nitrogen (N 2) as holes transport layer (HTL). The high PTV current ratio was achieved by evaporation of TPD under nitrogen gas ambient pressure 1×10 −4 Torr and iodine powder in weight ratio 10/1. Under low bias, the recombination between the low-energy holes in the dopant-induced guest-hopping sites and the electrons in lowest unoccupied molecular orbital (LUMO) only generates low-energy phonons, which scatter the carriers, thus leading to the NDR phenomenon. However, for high voltage, the recombination generates high-energy photons, thus enhancing the OLEDs output luminance. The doping of iodine and nitrogen promotes output luminance of OLED to 480%/200% and 200%/165% in magnitude under bias of 7 V/10 V, respectively.

High current density and high PVCR Si/Si 1−xGe x DQW RTD formed with quadruple-layer buffer

s As a strain-relief relaxed Si 1-x Ge x buffer that is used for type II band offset formation, we have proposed a quadruple-Si 1-x Ge x -layer (QL) buffer where misfit dislocations are evenly distributed in the lower two interfaces and a buffer surface with good crystallinity was obtained. The crystallinity of the buffer surface does not degrade by high P doping with a P concentration of ∼10 19 cm -3 during the buffer growth. A vertical-type electron-tunneling Si/Si 1-x Ge x resonant tunneling diode (RTD) formed with the highly P-doped QL buffer exhibits a high current density and a high peak-to-valley current ratio (PVCR) value. A planer-type electron-tunneling Si/ Si 1-x Ge x RTD formed with the same buffer using tetramethyl ammonium hydroxide (TMAH) etching and polyimide insulator, which is better suited for device integration, also exhibits a high current density and a high PVCR value and good initial static performance reproducibility.

Low sidewall damage plasma etching using ICP-RIE with HBr chemistry of Si∕SiGe resonant interband tunnel diodes

The effect and influence of dry plasma etching processes of Si/SiGe using HBr for the formation of diode mesa structures has been investigated to minimise sidewall leakage current. To characterise sidewall damage electrically, Si-based resonant interband tunnel diodes (RITD) were processed and the completed RITDs compared by their peak-to-valley current ratio (PVCR) and valley current density (VCD), which are sensitive to defect related currents. Dry processed RITDs were compared to reference RITDs fabricated by wet chemical etching (HNO3:HF:H2O=100:1:100). The combination of HBr process gas and very low substrate bias power (10 W) for inductively coupled plasma reactive ion etching (ICP-RIE) yielded the better results. The resulting RITDs processed by ICP-RIE using HBr chemistry show high PVCR of 4.02 with VCD of 32 A/cm2 while wet etched RITDs show a PVCR of only 2.81 with VCD of 40 A/cm2. Hydrogen passivation during the HBr plasma process may play a role that overcomes the slightly higher surface roughness compared to wet etching.

Si 1 − xGe x sputter epitaxy technique and its application to RTD

A Si 1 − x Ge x sputter epitaxy method using an ultra-high-vacuum-compatible magnetron sputtering technique with an Ar and H 2 mixture working gas has been introduced. The crystallinity and strain-relaxation controllability of a Si 1 − x Ge x layer grown on n-type Si(001) by our sputter epitaxy method is well comparable to those of a Si 1 − x Ge x layer grown by a standard molecular beam epitaxy (MBE) method. In the device level evaluation by forming an electron-tunneling Si/Si 1 − x Ge x asymmetric double quantum well resonant tunneling diode (ASDQW RTD), the fabricated RTD exhibits a high peak-to-valley current ratio (PVCR) of ∼ 26 with low background current, the performance of which is also close to that of our recent high PVCR ASDQW RTD fabricated by gas-source MBE. On the basis of these results, our proposed method is very promising for its application to various kinds of SiGe devices.

High PVCR Si/Si 1−xGe x DW RTD formed with new triple-layer buffer

A new thin triple-layer buffer consisting of three SiGe alloy layers is proposed for Si/Si 1− x Ge x resonant tunneling diodes (RTDs). The triple-layer buffer is compared to our previously proposed thin double-layer buffer with x being stepwise increased. The triple-layer buffer is formed by inserting an ultra-thin high Ge composition SiGe alloy layer between Si substrate and the thin double-layer buffer. By insertion of the ultra-thin high Ge composition SiGe alloy layer, the triple-layer buffer is more relaxed; however, the relaxation rate is limited to around 50% under our experimental conditions. Although the triple-layer buffer has still strain and the barrier height is relatively low, a double-well RTD using this buffer exhibits a peak-to-valley current ratio (PVCR) of as high as ∼50 000, which is far larger than that of standard III–V RTDs. The results also indicate that the proposed buffer leads to a high crystalline quality quantum well structure and that inelastic electron scattering in the Si/Si 1− x Ge x RTD is inherently low.

Physics and applications of Si/SiGe/Si resonant interband tunneling diodes

Room temperature (RT) current–voltage characteristics of Si/Si 1− x Ge x /Si p +-i-n + interband tunneling diodes are presented. The variation of the structural properties results in a more detailed picture of the tunneling process in these diodes, which allows further improvement of the relevant parameter. Special attention is paid to the peak current density (PCD) and the peak-to-valley current ratio (PVCR) of the devices. For an optimized structure with a 3-nm thick Si 0.54Ge 0.46 layer in the intrinsic zone a record PVCR of 6.0 at a PCD of approximately 1.5 kA/cm 2 was achieved. By reducing the layer thickness to 2.6 nm and simultaneously increasing the Ge content to 54%, the PCD increases to 30 kA/cm 2 at a high PVCR of 4.8.

Investigation of a Step-Doped-Channel Negative-Differential-Resistance Transistor

An interesting AlGaAs/InGaAs/GaAs step-doped channel negative-differential-resistance transistor (SDCNDRT) has been fabricated. The SDCNDRT is based on a previously reported step-doped-channel field-effect transistor (SDCFET). The N-shaped negative-differential resistance (NDR) are three-terminal-controlled NDR phenomena. We believe that the NDR phenomena can be attributed to the real space transfer (RST). A maximum drain current and peak-to-valley current ratio (PVCR) of 59 mA and 6.6 are obtained, respectively. The high drain current and PVCR indicate the potential of the SDCFET for practical circuit applications.

Multipeak NDR and high PVCR in GaAs/InGaAs/InAs multi-stepped quantum well resonant interband tunnelling diodes

The authors report a simple method for decreasing the valley current density and therefore increasing the peak-to-valley current ratio (PVCR) so that it reached 360 at room temperature in GaAs/In/sub 0.59/Ga/sub 0.41/As/InAs multi-stepped quantum well resonant interband tunnelling diodes (MSQW RITDs) using a GaAs undoping spacer layer. The PVCR is better data than that of other RITDs, to the knowledge of the authors. Multiple peak resonant tunnelling has been observed in this structure as the undoped GaAs spacer layer is involved.

Anomalous negative-differential-resistance (NDR) characteristics of step-doped-channel transistor (SDCT)

An Al0.3Ga0.7As/In0.15Ga0.85As/GaAs step-doped-channel transistor (SDCT) with anomalous three-terminal-controlled N-shaped negative-differential-resistance (NDR) phenomena has been fabricated and studied. The maximum drain current and peak-to-valley current ratio (PVCR) of 59 and 6.6 mA are obtained, respectively. The high drain current and PVCR can increase the range of potential applications in large signal and logic circuits. The authors believe that the NDR phenomena are attributed to real-space-transfer (RST) and the deep-level electron trapping effect.