Peak-to-valley Current Ratio Research Articles

Influence of tunneling barrier width on the forward current characteristics of InAs-based microwave p–n diode

InAs-based p–n interband tunneling bi-barrier resonant microwave (ITE BBRM) devices were successfully fabricated by using the molecular beam epitaxial (MBE) method in this research. The influence of a central barrier thickness from 10Å to 40Å on electrical characteristics of BBRM devices was investigated by using theoretical analysis and experimental evidence. Tunneling current densities (JT) of BBRM devices were simulated in accordance with the consideration of a narrowing bandgap (NBG) effect caused by the heavy concentration doped (HCD) effect. The peak-to-valley current ratio (PVCR) value and output current density reached as high as 383 and 0.226kA/cm2 in practice, respectively, when the central barrier thickness was 10Å thick. When an InAs-based p–n BBRM device produces a resonant phenomenon, the resonant operation voltage of the device is as low as 2.03V in our experimental study. Experimental results of the tunneling current density are matched to the calculating results of device from the calculation of quantum energy levels. The thinner the tunneling barrier thickness between the double quantum wells, the more the tunneling current density, which is attributed to the larger transmittance coefficient. In this study, an increase in the central barrier thickness increased the resistive cutoff frequency (fr), which the frequency reached GHz indicating that the ITE BBRM device became a microwave resonant device.

Optimum current‐voltage characteristics of GaAs/AlAs intraband microwave devices

In this reported work, both high peak current density and high peak-to-valley current ratio (PVCR) in AlAs/GaAs triple-barrier quantum-well intraband resonant tunnelling diodes (TBQW IRTDs) were accomplished. The valley current density (JV) of TBQW IRTDs can be degraded as the barrier thickness reaches 4 nm thickness. This result suggests narrow barrier thickness is due to the slight band bending effect in the conduction band of i -AlAs barrier layers. The peak current density (JP) of the TBQW IRTDs will be <2.43 KA/cm2 as the i -AlAs barriers thickness of the TBQW IRTD reaches 5 nm thickness. The optimal thickness of barrier layers should be selected at 4 nm thickness to obtain the highest PVCR value (about 4270), in which the sample with barrier layers of 4 nm thickness possesses the lowest valley current density.

Staggered band gap n+In0.5Ga0.5As/p+GaAs0.5Sb0.5 Esaki diode investigations for TFET device predictions

We study in this paper the epitaxial growth and electrical characterization of an n+In0.5Ga0.5As/p+GaAs0.5Sb0.5 Esaki diode lattice matched to (001)-oriented InP substrate. First, the effects of molecular beam epitaxy growth temperature and group-V growth rates on the GaAsxSb1−x composition are characterized by means of X-ray diffraction (XRD). It is found that GaAsxSb1−x lattice constant is mainly determined by the Sb4 incorporation rather than the As4 one. After optimization, high quality In0.54Ga0.46As(Si)/GaAs0.52Sb0.48(Be) heterostructure is confirmed by XRD, Transmission electron microscope (TEM) and Secondary Ion Mass Spectroscopy (SIMS) profiles meeting requirements for sub-60mV/dec operating devices. Esaki tunnel diodes are then fabricated to be used as a prediction of Band-To-Band Tunneling (BTBT) for Tunnel Field-Effect transistors (TFETs). The results are compared to previously reported n+/p+In0.5Ga0.5As homojunction diodes, showing a ×60 factor improvement of BTBT current density for the same electric field with an excellent average Peak-to-Valley Current Ratio (PVCR) of 14.

Multiple negative differential resistance devices with ultra-high peak-to-valley current ratio for practical multi-valued logic and memory applications

In this paper, we propose a novel multiple negative differential resistance (NDR) device with ultra-high peak-to-valley current ratio (PVCR) over 106 by combining tunnel diode with a conventional MOSFET, which suppresses the valley current with transistor off-leakage level. Band-to-band tunneling (BTBT) in tunnel junction provides the first peak, and the second peak and valley are generated from the suppression of diffusion current in tunnel diode by the off-state MOSFET. The multiple NDR curves can be controlled by doping concentration of tunnel junction and the threshold voltage of MOSFET. By using complementary multiple NDR devices, five-state memory is demonstrated only with six transistors.

Invited: III-Nitride Semiconductor Nanowire Resonant Tunneling Diodes

Resonant tunneling devices (RTDs) have attracted considerable interests because of their extremely high switching speeds and potential applications in multi-logic circuits. Due to the large conduction band offset, strong piezoelectric and spontaneous polarization, III-nitride wide band gap semiconductors are promising materials for resonant tunneling devices. However, III-nitride thin film structures always suffer from a large density of threading dislocations due to the large lattice matches between themselves and also substrates. Therefore negative differential resistances (NDR) reported in thin film III-nitride devices are a result of trap-assisted tunneling. III-nitride heterojunction nanowires have the potential to address this issue because that the large surface-to-volume ratio and small cross sections allows semiconductor nanowires accommodate much higher lattice mismatch with an efficient elastic strain relaxation thereby inhibiting the formation of dislocations. In this work, we demonstrate III-nitride nanowire RTDs with high tunneling current density and peak-to-valley current ratio. We started with growth of n-GaN/AlN/i-GaN/AlN/n-GaN double barrier heterojunction nanowres by plasma assisted molecular beam epitaxy. The I-V characteristics show clear NDR features at both room temperature and cryogenic temperatures. Significantly, NDR happens in both forward and backward voltage sweeps at the same bias, which is a strong evidence that NDR is a result of tunneling resonance as designed rather trap-assisted tunneling reported in III-N thin film heterostructures. A maximum peak to valley current ratio (PVCR) of 41 and a maximum resonant peak current density of 106 A/cm2 have been demonstrated. To our best knowledge, this is higher than any reported PVCR values in AlN/GaN RTDs. The details of the design, simulation, growth, and fabrication of such III-nitride heterojunction nanowire RTDs will be discussed in this talk.

Half-filled energy bands induced negative differential resistance in nitrogen-doped graphene.

Nitrogen-doping brings novel properties and promising applications into graphene, but the underlying mechanism is still in debate. To determine the key factor in motivating the negative differential resistance (NDR) behaviour of nitrogen-doped graphene, the electronic structure and transport properties of an 11-dimer wide nitrogen-doped armchair graphene nanoribbon (N-AGNR) were systematically studied by first principles calculations. Both the effect of interaction between N-dopants and the effect of doping-sublattice on the NDR were examined for the first time. Taking into account the two effects, N-AGNR becomes metallic or semiconducting depending on the doping configuration, and its Fermi level varies in a large range. NDR was firmly verified not to be intrinsic for N-AGNRs. However, it is totally determined by whether nitrogen-doping induces half-filled energy bands (HFEBs) because it is HFEBs that cross the Fermi level and determine the transport properties of N-AGNR under low biases. With the bias increasing, the transmission spectrum near the Fermi level showed a flag shape, and therefore, the corresponding transport channel is totally suppressed at a certain bias, resulting in the NDR behaviour with a configuration-dependent peak-to-valley current ratio (PVCR) up to 10(4). Our findings give new insights into the microscopic mechanism of chemical doping induced NDR behaviour and will be useful in building NDR-based nanodevices in the future.

Anodic Oxidation of Ultra-Thin Ti Layers on ITO Substrates and their Application in Organic Electronic Memory Elements

In this work, controlled anodic oxidation is reported for ultra-thin (3nm thick) titanium layers on indium tin oxide (ITO) coated glass substrates. A physical explanation is also provided for the origin of the delamination process of the Ti during the anodic oxidation. The properties of the fabricated layers are studied using electrochemical impedance spectroscopy (EIS) and X-ray Photoelectron Spectroscopy (XPS). In addition, one intriguing application is demonstrated for the anodized layers: their use as an interfacial barrier in organic diodes. Diodes containing an electrochemically fabricated TiO2 barrier layer exhibit clear room temperature negative differential resistance (NDR) and a peak-to-valley current ratio (PVCR) of 3.6. The reference diodes without the TiO2 layer show normal diode characteristics with no observable NDR. The NDR diodes have potential applications as memory elements for large-area electronics.

Effect of tensile strain on the negative differential resistance in the WTe2 armchair nanoribbon

In this work, we have studied the charge transport characteristics of WTe2 armchair nanoribbon and analyzed the variation in results by applying tensile strain to the nanoribbon. Tungsten ditelluride (WTe2) is a member of the transition metal dichalcogenides family. WTe2 is orthorhombic in structure with lattice parameters a = 0.6282 nm, b = 0.3496 nm, c = 1.407 nm. We have simulated the model using first-principle density functional tight binding theory and the non-equilibrium Green’s function method to study the effect of strain on the transport characteristics. The obtained results are compared with that of the perfectly relaxed nanoribbon. We have applied uniaxial (ϵxx) and biaxial (ϵxx = ϵyy) tensile strain to the nanoribbon. We present the ID-VDS characteristics, transmission spectrum and conductance for different cases. Negative differential resistance (NDR) is observed in all the cases along with a change in peak-to-valley current ratio (PVCR) and negative differential resistance region (NDRR).

Resonant tunneling with high peak to valley current ratio in SiO2/nc-Si/SiO2 multi-layers at room temperature

We have investigated carrier transport in SiO2/nc-Si/SiO2 multi-layers by room temperature current-voltage measurements. Resonant tunneling signatures accompanied by current peaks are observed. Carrier transport in the multi-layers were analyzed by plots of ln(I/V2) as a function of 1/V and ln(I) as a function of V1/2. Results suggest that besides films quality, nc-Si and barrier sub-layer thicknesses are important parameters that restrict carrier transport. When thicknesses are both small, direct tunneling dominates carrier transport, resonant tunneling occurs only at certain voltages and multi-resonant tunneling related current peaks can be observed but with peak to valley current ratio (PVCR) values smaller than 1.5. When barrier thickness is increased, trap-related and even high field related tunneling is excited, causing that multi-current peaks cannot be observed clearly, only one current peak with higher PVCR value of 7.7 can be observed. While if the thickness of nc-Si is large enough, quantum confinement is not so strong, a broad current peak with PVCR value as high as 60 can be measured, which may be due to small energy difference between the splitting energy levels in the quantum dots of nc-Si. Size distribution in a wide range may cause un-controllability of the peak voltages.

Asymmetrical Molecular Junctions with different Alligator Clips

This paper describes different molecular junctions with different alligator clips connected to gold electrodes at nanometre-scale. Our objective was to determine the charge transport characteristics of these junctions and determine the optimum alligator clip pair. We scrutinised anthracenedithiol (ADT), anthracenediamine (ADA) and anthracenethiolamine (ATA) and computed their conductance parameters through our simulations via Semi Emperical Extended Huckel Theory Approach. We aimed at finding that whether symmetrical (same alligator clips at each side) or asymmetrical (different alligator clips at each side) is the optimised approach to connect the anthracene molecule with gold electrodes and found that different alligator clips i.e. thiol and amine exhibited more conduction than that of same clip pair i.e. ADT and ADA. We further examined the effect of changing alligator clips positions from para to meta and found varied quantum interference effects. Peak to valley current ratios (PVR) for ADT was found to be maximum as 7.05 whereas meta ATA exhibited lowest peak to valley current ratio of 1.44. 

Negative Differential Resistance Devices with Ultra-High Peak-to-Valley Current Ratio and Its Multiple Switching Characteristics

We propose a novel negative differential resistance (NDR) device with ultra-high peak-tovalley current ratio (PVCR) by combining pn junction diode with depletion mode nanowire (NW) transistor, which suppress the valley current with transistor off-leakage level. Band-to-band tunneling (BTBT) Esaki diode with degenerately doped pn junction can provide multiple switching behavior having multi-peak and valley currents. These multiple NDR characteristics can be controlled by doping concentration of tunnel diode and threshold voltage of NW transistor. By designing our NDR device, PVCR can be over 10<SUP>4</SUP> at low operation voltage of 0.5 V in a single peak and valley current.

Fabrication of Al/MgO/C and C/MgO/InSe/C tunneling barriers for tunable negative resistance and negative capacitance applications

Abstract In this work, the design and characterization of magnesium oxide based tunneling diodes which are produced on Al and InSe films as rectifying substrates are investigated. It was found that when Al thin films are used, the device exhibit tunneling diode behavior of sharp valley at 0.15 V and peak to valley current ratio (PVCR) of 11.4. In addition, the capacitance spectra of the Al/MgO/C device show a resonance peak of negative capacitance (NC) values at 44.7 MHz. The capacitance and resistance–voltage characteristics handled at an ac signal frequency of 100 MHz reflected a build in voltage ( V bi ) of 1.29 V and a negative resistance (NR) effect above 2.05 V. This device quality factor ( Q )–voltage response is ~10 4 . When the Al substrate is replaced by InSe thin film, the tunneling diode valley appeared at 1.1 V. In addition, the PVCR, NR range, NC resonance peak, Q and V bi are found to be 135, 0.94–2.24 and 39.0 MHz, ~10 5 and 1.34 V, respectively. Due to the wide differential negative resistance and capacitance voltage ranges and due to the response of the C/MgO/InSe/C device at 1.0 GHz, these devices appear to be suitable for applications as frequency mixers, amplifiers, and monostable–bistable circuit elements (MOBILE).

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.

SPICE Modeling of the Scaling of Resonant Tunneling Diodes and the Effects of Sidewall Leakage

Si/SiGe and AlGaAs/GaAs resonant tunneling diodes (RTDs) are realized using a self-aligned fabrication process with dimensions ranging from 50 μm down to 30 nm. Using these devices, scaling rules are developed and incorporated into a modified SPICE model. The depletion width and the sidewall current are extracted from the model. The results confirm that the parasitic sidewall current is responsible for the reduction in peak-to-valley current ratio (PVCR) in small-diameter RTDs. A new device layout is demonstrated to significantly reduce the sidewall current for optimum nanoscale performance. Improvements in the PVCRs are demonstrated by this approach.

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.

Boron Delta-Doping Dependence on Si/SiGe Resonant Interband Tunneling Diodes Grown by Chemical Vapor Deposition

Si/SiGe resonant interband tunnel diodes (RITD) were fabricated using CVD on 200-mm silicon wafers. The RITD devices consist of a p <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> -i-n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> structure with δ-doped quantum wells providing resonant interband tunneling through a nominally intrinsic Si/SiGe region. The vapor-phase doping technique was used to obtain abrupt degenerate doping profiles. The boron doping in the δ-doped region was varied, and its effect on peak current density <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Jp</i> and peak-to-valley current ratio (PVCR) was studied. As the flow rate is reduced, <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Jp</i> was found to reduce while the PVCR initially increases and then decreases. Device simulations were performed using the ATLAS simulator developed by SILVACO to interpret the results. A maximum PVCR of 2.95 was obtained, and the highest <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Jp</i> recorded was 600 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . This is the highest reported PVCR for any CVD-grown Si/SiGe RITD.

Detemining the Thickness of Barriers and Well of Resonance Tunneling Diodes by Specified I-V Characteristic

In this paper, a method of determining physical dimension of Double Barrier Quantum Well (DBQW) of Resonance Tunneling Diodes (RTDs) is presented by using I-V characteristic governing on them. In this procedure, first we have used performance metrics related to RTDs I-V characteristic such as Peak to Valley Current Ratio (PVCR), peak current density (JP), valley current density (JV) and Voltage Swing (VS), and by some other arbitrary points, we have fitted a curve to the RTD current-voltage equation by MATLAB software. Then we have obtained the physical parameter of I-V equation and adjusted some of them with modification coefficients. Next, by choosing the material of barriers and the well and amount of doping, we have calculated the thicknesses of both. To review the mentioned method, the experimental result of I-V characteristic of the sample structure DBQW is considered and we have come to this idea that the dimensions gained out of this method are highly correlated with those of the experimental sample.

Tunneling Effects in DNA bases Adenine and Guanine

Molecular electronics has been the centre stage of research recently. Much interest has been shown by scientists in exploring the electrical and electronic properties of DNA. In this paper DNA bases Adenine and Guanine are being explored for its use as tunneling device. The molecules are applied variable bias voltage ranging from –5V to +5V to observe the flow of current using two-probe setup of Virtual Nanolab. The current–voltage characteristics obtained resemble typical tunnel diode characteristic with display of resonant tunneling phenomenon in the molecule. The two molecules Adenine and Guanine exhibit Negative Differential Resistance with a considerably large Peak to Valley Current Ratio (PVR). The observations suggest that the two molecules may be used in molecular resonant devices. The NDR characteristic suggests useful utilization of the proposed device in nanoscale digital circuits. Also the large value of PVR supports the use of Adenine in power saving highdensity integrated circuits.

Extremely High Peak Current Densities of over 1×106 A/cm2 in InP-Based InGaAs/AlAs Resonant Tunneling Diodes Grown by Metal–Organic Vapor-Phase Epitaxy

InP-based InGaAs/AlAs resonant tunneling diodes (RTDs) with extremely high peak current density ( jP) were grown by metal–organic vapor-phase epitaxy. High-temperature growth at 660 °C provides high-quality heterointerfaces and excellent current–voltage (I–V) characteristics. To obtain extremely high jP, the structural parameter dependence of I–V characteristics on barrier and spacer thicknesses and emitter-doping concentration were examined. Clear exponential dependence of jP on barrier thickness was obtained in the barrier-thickness range from 1.2 to 2.8 nm. The reduction of spacer thickness to 2 nm increased jP without deteriorating the peak-to-valley current ratio (PVR). An investigation of Si dopant diffusion into double-barrier regions at the growth temperature supports the validity of reducing spacer thickness. The jP increased as Si doping concentration was increased from 1×1018 to 6×1018 cm-3 in InGaAs emitters. The highest jP reached 1.29×106 A/cm2 with a PVR of 1.5 in a RTD at room temperature with barrier and spacer thicknesses of 1.4 and 2 nm and Si doping concentration in the emitter of 6×1018 cm-3.

High-Performance Single Nanowire Tunnel Diodes

We demonstrate single nanowire tunnel diodes with room temperature peak current densities of up to 329 A/cm(2). Despite the large surface to volume ratio of the type-II InP-GaAs axial heterostructure nanowires, we measure peak to valley current ratios (PVCR) of up to 8.2 at room temperature and 27.6 at liquid helium temperature. These sub-100-nm-diameter structures are promising components for solar cells as well as electronic applications.