Transition times between the extremum points of the current–voltage characteristic of a resonant tunneling diode with hysteresis

A numerical solution to the problem of transient processes in a resonant tunneling diode featuring a current–voltage characteristic with hysteresis is found for the first time in the context of a coherent model (based on the coupled Schrödinger and Poisson equations) taking into account the Fermi distribution of electrons. The transitions from the high-current to the low-current state and vice versa, which result from the existence of hysteresis and are of great practical importance for ultrafast switches based on resonant tunneling diodes, are studied in detail. It is shown that the transition times for such processes initiated by the application of a small voltage can significantly exceed the characteristic time ?/Γ (where G is the width of the resonance level). It is established for the first time that the transition time can be reduced and made as short as the characteristic time ?/Γ by applying a sufficiently high voltage. For the parameters of the resonant-tunnelingdiode structure considered in this study, the required voltage is about 0.01 V.     

Experimental determination of the derivative of the current–voltage characteristic of a nonlinear semiconductor structure using modulation Fourier analysis

The derivative of the nonlinear current–voltage characteristic of two antiparallel p–n junctions is experimentally obtained by the method of modulation Fourier analysis. The derivative of the current–voltage characteristic is reconstructed using the current dependences of the first and higher voltage harmonics. The advantage of modulation Fourier analysis over numerical differentiation is experimentally validated for the first time. The applied technique has no limitations on the current modulation amplitude. Large amplitudes make it possible to identify the nature of the nonlinearity of the dependence under study and to determine the contribution of the nonlinear fraction against the background of significant linearity.     

Simplified model for ballistic current–voltage characteristic in cylindrical nanowires

The ballistic regime gives the upper limit of an electron device performance. This paper proposes a fast and efficient model for calculating the current–voltage characteristic of a cylindrical nanowire within the framework of the non-equilibrium Green's function. Under certain assumptions, the calculation is simplified to a one-dimensional problem and the modes due to the radial confinement are given by an analytical equation. We further derive an analytical expression for the current–voltage characteristic at temperature approaching 0 K. The relationship between the radius of the nanowire and the electrical current is clearly shown in this expression. The effects of the radius on the current–voltage characteristic curve are also studied. Furthermore, we plot the trend of the saturation current as the radius is increased as predicted by both the numerical result and our analytical model. Our proposed model can be further used to include electron–photon interaction in the calculation of nanoscale optoelectronic 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.     

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.     

Physical parameters extraction from current–voltage characteristic for diodes using multiple nonlinear regression analysis

In this work, the two-step iteration combined with the nonlinear multiple regression technique to extract physical parameters for diodes, using a simple physical-based current–voltage (I–V) model is demonstrated. This statistical method can be applied for sampling for a wide variety of diodes including light-emitting diodes (LEDs) and Schottky diodes. Our results show the technique is an accurate and systematic approach for extracting diode parameters. The calculated recombination currents indicate the recombination efficiency for LEDs and the quality for Schottky diodes.     

A technique to improve the linearization of frequency–voltage characteristic of LC-VCO

This paper presents a very low-power linearization technique to improve the linearity of frequency-voltage characteristic of LC-VCO (voltage controlled oscillator) using MOS varactor. This reduces the VCO gain (K _VCO) variation and its required value over the tuning voltage range. Low K _VCO improves noise and reference spur performances at the output of phase lock loop/frequency synthesizer (FS). Low K _VCO variation reduces FS loop stability problem. Using this VCO circuit, a fully on-chip integer-N frequency synthesizer has been fabricated in 0.18 μm epi-digital CMOS technology for 2.45 GHz ZigBee application. The measured VCO phase noise is ?115.76 and ?125.23 dBc/Hz at 1 and 3 MHz offset frequencies, respectively from 2.445 GHz carrier and the reference spur of the frequency synthesizer is ?68.62 dBc. The used supply voltage is 1.5 V.     

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.     

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.     

Circuital modelling of S-shape removal in the current–voltage characteristic of TiOx inverted organic solar cells through white-light soaking

In this work light activation phenomenon in inverted bulk heterojunction (BHJ) organic solar cells (OSC) has been electrically modelled with a two-diode equivalent circuit. OSC are based on poly(3-hexylthiophene) (P3HT): 1-(3-methoxycarbonyl)-propyl-1-1-phenyl-(6,6) C61 (PCBM) with a titanium oxide (TiO_x) sublayer. Current–voltage (I–V) characteristics show a highly pronounced S-shape that is gradually removed during light activation process. The circuit used to model I–V curves includes two diodes in forward and reverse bias together with two parallel resistances, R_P1 and R_P2. The parallel of the reverse bias diode and its corresponding resistance R_P2 models the electrical behaviour of the TiO_x interlayer. This interlayer has been thermally treated at different temperatures, from 80 °C up to 180 °C, reducing the activation time from 400 s for unbaked devices down to 30 s for devices annealed at temperatures higher than 80 °C. The S-shape shown in the I–V characteristic is completely removed after a few minutes of white-light illumination. I–V curves recorded during the activation process have been fitted with the analytical solution of the two-diode circuit based on W-Lambert function. A decrease of the subcircuit 2 equivalent resistance has been found to be the cause of S-shape removal. This resistance diminishing is in good agreement with the increase of TiO_x conductance with baking temperature and white-light exposure time found by other authors.     

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.     

Investigation of current–voltage characteristics of vertically stacked all-NbCN Josephson junctions

Current–voltage characteristics of vertically stacked all-NbCN Josephson junctions has been investigated with a purpose to use them as an element of integrated circuits. It has been shown that increases of microwave power in the junction definition process using electron cyclotron resonance (ECR) etching causes reduction of the junction quality parameter. From results of a measurement of current–voltage characteristics for an array composed of five-fold vertically stacked NbCN/MgO/NbCN junctions, it has been found that a very high uniformity in critical currents can be achieved.     

The influence of a voltage ramp on the measurement of I–V characteristics of a solar cell

For convenience and efficiency the voltage applied to a Si solar cell is often fairly rapidly driven from zero to the open circuit value typically at a constant rate of 1 V per millisecond. During this time the values of the current are determined as a function of the instantaneous voltage thus producing an I–V characteristic. It is shown here that the customary expressions for the current as a function of cell parameters remain still valid provided that the diffusion length in the expression for the dark current is changed from its steady state value L to the effective diffusion length L_i given by

$\text{L}{}_1\text{= L}\text{1+}\text{q}\text{V}\text{?}\text{kT}{}^{\mathrm{\tau }}\text{,}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$

where V is the ramp rate considered constant and τ is the lifetime of minority carriers. This result is true to a very good approximation provided that low level injection prevails.     

Cd x Hg1 − x Te-based photodetector with the spectral characteristic controlled by the voltage

A photodetector with a spectral characteristic of the photoresponse controlled by the bias voltage is realized on the basis of the Al-n-Cd _x Hg_{1 ? x} Te heterostructure with a narrow insulator gap. The features of the spectral characteristic of the photocurrent are accounted for by the variation in the ratio between the surface and bulk components of the photocurrent upon varying the bias voltage. The possibility of simultaneous detection and control over the spectral characteristic of photosensitivity at the fundamental adsorption edge and in the short-wavelength spectral region is shown.

     

Development of Fiber Optically Driven Instrument for High—voltage Line Current

The measurement theorem of fiber optically driven instrument for high-voltage line current is presented.The PLL voltage-frequency-narrow pulse principle and its micro-consuption mechanism are proposed.followed by anayssis on the two main factors affecting PLL measurement precision.A software desighn scheme using 80C196KB mciro-controller is introduced.The experiment results is satisfactory.     

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.     

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.     

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.