Critical current–gate voltage characteristics in short- and long-gated Josephson junctions

We studied the gate controllability of the critical current and the normal resistance in superconductor–semiconductor–superconductor junctions. The junctions used a two-dimensional electron gas (2DEG) in the InAs-inserted InAlAs/InGaAs heterostructure. It is shown that the interface barrier between the superconductor and the 2DEG affects the controllability in a short-gated junction. In a split-gated junction, the critical current–normal resistance product is almost constant against gate voltage. This is due to quantization of both the critical current and the conductance in a narrow and short semiconductor channel. The long-gated junction in the quasi-ballistic transport regime shows rapid suppression of the critical current by gate voltage.     

Estimation of built-in voltage from steady-state current–voltage characteristics of organic diodes

A technique for extraction of built-in voltage from the steady-state current–voltage characteristics of a two terminal organic diode is described which does not require assumption of quadratic dependence of current on voltage. The technique relies instead on current voltage characteristics being exponential below built-in voltage and power-law above it to generate a sharply defined peak at a voltage proportional to built-in voltage. Simulation results are used to validate the proposed method and experimental results obtained with P3HT and P3HT:PCBM blends are presented.     

Intrinsic current–voltage characteristics of metal-carbon nanotube networks: A first-principles study

The interconnections involving metal atoms in single-walled carbon nanotube (SWNT) networks are crucial for building nanoscaled devices. The influence of the metal-(η⁶-SWNT) interconnects in the electrical conductivity of SWNT film have been reported in recent experiments [X. Tian et al. Nano lett. 2014,14,3930]. Using non-equilibrium Green's function with density function theory, we performed theoretical calculations on the electron transport properties of (Cr, Li, Au)-SWNT systems. We revealed the roles of transition metal Cr, alkalis metal Li and inert metal Au in improving the electrical conductance of metal-SWNT systems. Our calculated results show that transport properties along the inter-tube direction are strongly dependent on the connecting metal atoms varying over many orders of magnitudes. Gold atoms fail to enhance the electrical conductance of SWNT systems. Meanwhile, negative differential resistances are demonstrated in semiconducting inter-tube models, which would have potential applications in the electronic device. Our results provide a promising way to optimize the performance of SWNT based networks.     

Engineering the current–voltage characteristics of metal–insulator–metal diodes using double-insulator tunnel barriers

The femtosecond-fast transport in metal–insulator–metal (MIM) tunnel diodes makes them attractive for applications such as ultra-high frequency rectenna detectors and solar cells, and mixers. These applications impose severe requirements on the diode current–voltage I(V) characteristics. For example, rectennas operating at terahertz or higher frequencies require diodes to have low resistance and adequate nonlinearity. To analyze and design MIM diodes with the desired characteristics, we developed a simulator based on the transfer-matrix method, and verified its accuracy by comparing simulated I(V) characteristics with those measured in MIM diodes that we fabricated by sputtering, and also with simulations based on the quantum transmitting boundary method. Single-insulator low-resistance diodes are not sufficiently nonlinear for efficient rectennas. Multi-insulator diodes can be engineered to provide both low resistance and substantial nonlinearity. The improved performance of multi-insulator diodes can result from either resonant tunneling or a step change in tunneling distance with voltage, either of which can be made to dominate by the appropriate choice of insulators and barrier thicknesses. The stability of the interfaces in the MIIM diodes is confirmed through a thermodynamic analysis.     

Influences of magnetic fields on current–voltage characteristics of gold-DNA-gold structure with variable gaps

Achieving highly sensitive magnetic sensors by means of Metal-DNA-Metal (MDM) structure is a key issue. DNA, being a genetic information carrier in living cells reveals tunable semiconducting response in the presence of external electric and magnetic fields, which is promising for molecular electronics. The influence of magnetic fields up to 1200 mT on the current–voltage (I–V) behavior of Gold-DNA-Gold (GDG) structure having variable gap sizes from 20–50 μm are reported in this work. These structures were fabricated using UV lithography, DC magnetron sputtering and thermal evaporation techniques. DNA strands were extracted from Boesenbergia rotunda plant via standard protocol. The acquired I–V characteristics display the semiconducting diode nature of DNA in GDG structures. The potential barrier for all the structures exhibit an increasing trend with the increase of externally imposed magnetic field irrespective of variable gap sizes. Furthermore, the potential barrier in GDG junction at higher magnetic field strengths (>1000 mT) is found to be considerably enhanced. This enhancement in the junction barrier height at elevated magnetic fields is attributed to the reduction of carrier mobility and augmentation of resistance. The achieved admirable features of magnetic sensitivity suggest the viability of using these GDG sandwiches as a prospective magnetic sensor.     

Methods for measuring the current–voltage characteristics of photodiodes in a multirow infrared photodetector

Methods for measuring the current-voltage characteristics (I–V curves) of photodiodes in a 6 × 576 mercury-cadmium-tellurium (MCT) multirow photodetector designed for operation in the longwave part of the infrared (IR) spectral range are analyzed. The I–V curve is plotted using the resultes of measurements of output signals of a large-scale readout integrated circuit (ROIC) hybridized with a row of IR photodiodes. The method of independent current measurement at each point of the I–V curve is compared to the method of additive current measurements. A method of determining optimum working points of photodiodes by plotting and analyzing the dependence of the differential resistance of photodiode on the bias voltage is proposed. Distributions of photodiode currents for a sample of a 6 × 576-element focal plane array (FPA) based on MCT photodiodes with a p-type conductivity substrate having the cutoff wavelength of λ_0.5 = 10.5 μm are considered.     

Calculation of the Schottky barrier and current–voltage characteristics of metal–alloy structures based on silicon carbide

A simple but nonlinear model of the defect density at a metal–semiconductor interface, when a Schottky barrier is formed by surface defects states localized at the interface, is developed. It is shown that taking the nonlinear dependence of the Fermi level on the defect density into account leads to a Schottky barrier increase by 15–25%. The calculated barrier heights are used to analyze the current–voltage characteristics of n-M/p-(SiC)_1–x(AlN)_x structures. The results of calculations are compared to experimental data.     

Numerical simulation study of current–voltage characteristics of a Schottky diode with inverse doped surface layer

The Poisson’s equation and drift–diffusion equations are used to simulate the current–voltage characteristics of Schottky diode with an inverse doped surface layer. The potential inside the bulk semiconductor near the metal–semiconductor contact is estimated by simultaneously solving these equations, and current as a function of bias through the Schottky diode is calculated for various inverse layer thicknesses and doping concentrations. The Schottky diode parameters are then extracted by fitting of simulated current–voltage data into thermionic emission diffusion equation. The obtained diode parameters are analyzed to study the effect of inverse layer thickness and doping concentration on the Schottky diode parameters and its behavior at low temperatures. It is shown that increase in inverse layer thickness and its doping concentration give rise to Schottky barrier height enhancement and a change in the ideality factor. The temperature dependences of Schottky barrier height and ideality factor are studied. The effect of temperature dependence of carrier mobility on the Schottky diode characteristics is also discussed.     

Temperature dependent of the current–voltage (I–V) characteristics of TaSi2/n-Si structure

Tantalum silicide (TaSi₂) thin films were deposited on n-type silicon single crystal substrates using a dual electron-gun system and with Ta and Si targets. The electrical transport properties of the TaSi₂/n-Si structures were investigated by temperature-dependent current–voltage (I–V) measurements. The temperature-dependent I–V characteristics revealed that the forward conduction was determined by thermionic-emission and space-charge-limited current mechanisms at low and high voltage respectively. On the other hand, the reverse current is limited by the carrier generation process.     

Optically-induced effects in Y–ba–cu–O Josephson junctions

We report our studies on light-induced changes in electrical properties of YBa₂Cu₃O_x (YBCO) grain-boundary Josephson weak links. We discuss the erasable process (photodoping), in which light-induced enhancement of junctions properties at low temperatures relaxes back above 250 K. Our studies are focused on the junction critical current versus time, light intensity, and magnetic field measurements. In tested few-μm-wide step-edge junctions, photodoping manifested itself as above 50% increase of the critical current and the decrease of the junction magnetic penetration depth, leading to reduction of the effective junction width. Contrary to the photodoping effect, the high-intensity laser modification of junctions led to permanent modification of their electrical characteristics that remained unchanged after subsequent room-temperature/helium thermal cycling of the sample. The laser-modified junctions exhibited up to 25% increase of the critical current times normal-state resistance product.     

Theoretical and experimental studies of the current–voltage and capacitance–voltage of HEMT structures and field-effect transistors

The sensitivity of classical n ⁺/n ^– GaAs and AlGaN/GaN structures with a 2D electron gas (HEMT) and field-effect transistors based on these structures to γ-neutron exposure is studied. The levels of their radiation hardness were determined. A method for experimental study of the structures on the basis of a differential analysis of their current–voltage characteristics is developed. This method makes it possible to determine the structure of the layers in which radiation-induced defects accumulate. A procedure taking into account changes in the plate area of the experimentally measured barrier-contact capacitance associated with the emergence of clusters of radiation-induced defects that form dielectric inclusions in the 2D-electron-gas layer is presented for the first time.     

Temperature dependence of current–voltage characteristics of MoS2/Si devices prepared by the chemical vapor deposition method

Layers of MoS₂ are directly deposited on the n-type Si (n-Si) substrate by chemical vapor deposition for fabricating a MoS₂/n-Si heterojunction device. The rectification current–voltage (I–V) characteristics of MoS₂/n-Si devices were measured in the temperature range from 80 to 300 K in steps of 20 K. The temperature-dependent forward-bias I–V characteristics can be explained on the basis of the thermionic emission theory by considering the presence of the interfacial inhomogeneous barriers at the MoS₂/n-Si interfaces. The dominance of the induced carrier capture/recombination by states at the MoS₂/n-Si interface that lead to the formation of the inhomogeneous barriers serves to influence the photo-response at room temperature. The fabricated MoS₂/n-Si devices exhibit reversible switching between high and low current densities, when the simulated sunlight is turned on and off. The sensitivity of the I–V characteristics to temperature provides an opportunity to realize stable and reliable rectification behaviors in the MoS₂/n-Si devices. It is found that the electron mobility in the n-Si layer reduces as temperature increases, which leads to the noticeably increased value of the series resistance of MoS₂/n-Si devices.     

Investigation of ESD protection strategy in high voltage Bipolar–CMOS–DMOS process

This paper presents device optimization and physical analysis based on gate-grounded NMOS (GGNMOS) and n-channel lateral DMOS (nLDMOS) devices manufactured in a 0.35 μm 5 V/30 V high-voltage BCD process. The multiple body pick-up technique has been investigated in detail for the GGNMOS, and the robustness and effectiveness of the LDMOS device is optimized by tuning the drain contact to gate space (DCGS) and increasing the body resistance. Finally, the trigger voltage walk-in effect is observed for the nLDMOS device and is studied by comprehensive simulation and TLP tests.     

Capacitance–conductance–current–voltage characteristics of atomic layer deposited Au/Ti/Al2O3/n-GaAs MIS structures

We have studied the admittance and current–voltage characteristics of the Au/Ti/Al₂O₃/n-GaAs structure. The Al₂O₃ layer of about 5 nm was formed on the n-GaAs by atomic layer deposition. The barrier height (BH) and ideality factor values of 1.18 eV and 2.45 were obtained from the forward-bias ln I vs V plot at 300 K. The BH value of 1.18 eV is larger than the values reported for conventional Ti/n-GaAs or Au/Ti/n-GaAs diodes. The barrier modification is very important in metal semiconductor devices. The use of an increased barrier diode as the gate can provide an adequate barrier height for FET operation while the decreased barrier diodes also show promise as small signal zero-bias rectifiers and microwave. The experimental capacitance and conductance characteristics were corrected by taking into account the device series resistance R_s. It has been seen that the non-correction characteristics cause a serious error in the extraction of the interfacial properties. Furthermore, the device behaved more capacitive at the reverse bias voltage range rather than the forward bias voltage range because the phase angle in the reverse bias has remained unchanged as 90° independent of the measurement frequency.     

Current–voltage characteristics of organic heterostructure devices with insulating spacer layers

The dark current density in donor/acceptor organic planar heterostructure devices at a given forward voltage bias can either increase or decrease when an insulating spacer layer is added between the donor and acceptor layers. The dominant current flow process in these systems involves the formation and subsequent recombination of interfacial exciplex states. If the exciplex recombination rate limits current flow, an insulating interface layer decreases the dark current. However, if the exciplex formation rate limits the current, an insulating interface layer may increase the dark current. We present a device model to describe this behavior, and we discuss relevant experimental data.     

Current–voltage characteristics of Schottky diode simulated using semiconductor device equations

The Poisson's equation and the drift diffusion equations have been used to simulate the current–voltage characteristics of Schottky diode. The potential variation inside the bulk semiconductor near the metal–semiconductor contact was estimated first and then the current as a function of bias through the Schottky diode using silicon parameters were calculated over a wide temperature range. From the simulated current–voltage characteristics the diode parameters were extracted by fitting of current–voltage data into thermionic emission diffusion current equation. The derived barrier parameters are analysed to study the effect of various parameters, e.g. semiconductor thickness, doping concentration, temperature dependence of carrier mobility and energy band gap, on the current–voltage characteristics of Schottky diode in view of the thermionic emission diffusion current equations.     

Specific features of the current–voltage characteristics of SiO2/4H-SiC MIS structures with phosphorus implanted into silicon carbide

The effect of phosphorus implantation into a 4H-SiC epitaxial layer immediately before the thermal growth of a gate insulator in an atmosphere of dry oxygen on the reliability of the gate insulator is studied. It is found that, together with passivating surface states, the introduction of phosphorus ions leads to insignificant weakening of the dielectric breakdown field and to a decrease in the height of the energy barrier between silicon carbide and the insulator, which is due to the presence of phosphorus atoms at the 4H-SiC/SiO₂ interface and in the bulk of silicon dioxide.     

Study on the basic capacitance–voltage characteristics of organic molecular semiconductors

Capacitance–voltage (C–V) characteristics of organic molecular semiconductors attracted much research interest recently, but no convincing physical mechanism has been established so far. In this work, the C–V characteristics of pentacene-based devices have been systematically investigated at various frequencies. Only one peak occurs when the measuring frequency is less than 3 kHz or greater than 8 kHz. While within the frequency range between the two, two C–V peaks are observed with quite different dependence on temperature, which suggests that the origins of these two C–V peaks are respectively mobile holes and trapped carriers. This conclusion is also experimentally validated with the C–V characteristics of intentionally doped devices.     

Effect of transverse electric field on the longitudinal current–voltage characteristic of graphene superlattice

The current density induced along the axis of graphene superlattice in the presence of ac and dc electric fields has been calculated. The dc electric field vector is assumed to have both transverse and longitudinal components with respect to the superlattice axis. The constant component of the current density is shown to oscillate with a change in the ac field amplitude. The longitudinal current–voltage characteristic of graphene superlattice contains a portion with negative differential conductivity. The maximum of the longitudinal current–voltage characteristic shifts to larger values of the longitudinal component of dc field with an increase in the transverse component of electric field.     

Current–voltage and capacitance–voltage characteristics of Al Schottky contacts to strained Si-on-insulator in the wide temperature range

The electrical characteristics of Al/strained Si-on-insulator (sSOI) Schottky diode have been investigated using current–voltage (I–V) and capacitance–voltage (C–V) measurements in the wide temperature range of 200–400 K in steps of 25 K. It was found that the barrier height (0.57–0.80 eV) calculated from the I–V characteristics increased and the ideality factor (1.97–1.28) decreased with increasing temperature. The barrier heights determined from the C–V measurements were higher than those extracted from the I–V measurements, associated with the formation of an inhomogeneous Schottky barrier at the interface. The series resistance estimated from the forward I–V characteristics using Cheung and Norde methods decreased with increasing temperature, implying its strong temperature dependence. The observed variation in barrier height and ideality factor could be attributed to the inhomogeneities in Schottky barrier, explained by assuming Gaussian distribution of barrier heights. The temperature-dependent I–V characteristics showed a double Gaussian distribution with mean barrier heights of 0.83 and 1.19 eV and standard deviations of 0.10 and 0.16 eV at 200–275 and 300–400 K, respectively. From the modified Richardson plot, the modified Richardson constant were calculated to be 21.8 and 29.4 A cm⁻² K⁻² at 200–275 and 300–400 K, respectively, which were comparable to the theoretical value for p-type sSOI (31.6 A cm⁻² K⁻²).