Wide Range Of Electric Fields Research Articles

Interplay of Coulomb blockade and ferroelectricity in nanosized granular materials

We study electron transport properties of composite ferroelectrics---materials consisting of metallic grains embedded in a ferroelectric matrix. In particular, we calculate the conductivity in a wide range of temperatures and electric fields, showing pronounced hysteretic behavior. In weak fields, electron cotunneling is the main transport mechanism. In this case, we show that the ferroelectric matrix strongly influences the transport properties through two effects: (i) the dependence of the Coulomb gap on the dielectric permittivity of the ferroelectric matrix, which in turn is controlled by temperature and external field, and (ii) the dependence of the tunneling matrix elements on the electric polarization of the ferroelectric matrix, which can be tuned by temperature and applied electric field as well. In the case of strong electric fields, the Coulomb gap is suppressed and only the second mechanism is important. Our results are important for (i) thermometers for precise temperature measurements and (ii) ferrroelectric memristors.

Effect of burst and recombination models for Monte Carlo transport of interacting carriers in a-Se x-ray detectors on Swank noise

The authors describe the modification to a previously developed Monte Carlo model of semiconductor direct x-ray detector required for studying the effect of burst and recombination algorithms on detector performance. This work provides insight into the effect of different charge generation models for a-Se detectors on Swank noise and recombination fraction. The proposed burst and recombination models are implemented in the Monte Carlo simulation package, ARTEMIS, developed by Fang et al. ["Spatiotemporal Monte Carlo transport methods in x-ray semiconductor detectors: Application to pulse-height spectroscopy in a-Se," Med. Phys. 39(1), 308-319 (2012)]. The burst model generates a cloud of electron-hole pairs based on electron velocity, energy deposition, and material parameters distributed within a spherical uniform volume (SUV) or on a spherical surface area (SSA). A simple first-hit (FH) and a more detailed but computationally expensive nearest-neighbor (NN) recombination algorithms are also described and compared. Simulated recombination fractions for a single electron-hole pair show good agreement with Onsager model for a wide range of electric field, thermalization distance, and temperature. The recombination fraction and Swank noise exhibit a dependence on the burst model for generation of many electron-hole pairs from a single x ray. The Swank noise decreased for the SSA compared to the SUV model at 4 V/μm, while the recombination fraction decreased for SSA compared to the SUV model at 30 V/μm. The NN and FH recombination results were comparable. Results obtained with the ARTEMIS Monte Carlo transport model incorporating drift and diffusion are validated with the Onsager model for a single electron-hole pair as a function of electric field, thermalization distance, and temperature. For x-ray interactions, the authors demonstrate that the choice of burst model can affect the simulation results for the generation of many electron-hole pairs. The SSA model is more sensitive to the effect of electric field compared to the SUV model and that the NN and FH recombination algorithms did not significantly affect simulation results.

Direct Molecular Dynamics Simulation of Electrocaloric Effect in BaTiO3

The electrocaloric effect (ECE) in BaTiO3 is simulated using two different first-principles based effective Hamiltonian molecular dynamics methods. The calculations are performed for a wide range of temperatures (30–900 K) and external electric fields (0–500 kV/cm). As expected, a large adiabatic temperature change, ΔT, at the Curie temperature, TC, is observed. It is found that for single crystals of pure BaTiO3, the temperature range where a large ΔT is observed is narrow for small external electric fields (<50 kV/cm). Large fields (>100 kV/cm) may be required to broaden the effective temperature range. The effect of crystal anisotropy on the ECE ΔT is also investigated. It is found that applying an external electric field along the [001] direction has a larger ECE than those along the [110] and [111] directions.

Electron Transport Characteristics of Wurtzite GaN

A three-valley Monte Carlo simulation approach was used to investigate electron transport in wurtzite GaN such as the drift velocity, the drift mobility, the average electron energy, energy relaxation time, and momentum relaxation time at high electric fields. The simulation accounted for polar optical phonon, acoustic phonon, piezoelectric, intervalley scattering, and Ridley charged impurity scattering model. For the steady-state transport, the drift velocity against electric field showed a negative differential resistance of a peak value of 2.9×105 m/s at a critical electric field strength 180×105 V/m. The electron drift velocity relaxes to the saturation value of 1.5×105 m/s at very high electric fields. The electron velocities against time over wide range of electric fields are reported.

A Test Circuit for Extremely Low Gate Leakage Current Measurement of 10 aA for 80 000 MOSFETs in 80 s

We discuss the measurement accuracy of the test circuit, which can evaluate statistical characteristics of gate leakage current of small area metal-oxide-semiconductor field-effect transistors (MOSFETs) in a very short time. The accuracy and precision of the gate leakage current obtained by the test circuit are verified for a wide range. As a result it is confirmed that very accurate gate current of 10-17 A ±10% is able to be measured with this method. Using this test circuit, we can evaluate the gate leakage current at a wide electric field range, which is important in discussing the conduction mechanism of gate leakage current.

DESIGN OF A SAMPLE HOLDER FOR LOW TEMPERATURE ELECTRICAL CONDUCTIVITY MEASUREMENTS

Both DC and AC electrical conductivity of materials provide a number of valuable informationon the nature of current carriers, 3-D effects, scattering by defects and impurities, formation of CDW, soliton propagation, non – linear and switching phenomenon and other characters pertaining to these compounds. These measurements are therefore carried out over a wide range of temperature, pressure, electric fields and impurity concentrations. Besides these, the low temperature studies of the materials are performed to determine Optical and Magnetic properties and etc. Therefore, a suitable sample holder is required to perform these studies with low temperature variations. In this paper, we report a design of such a suitable and simple sample holder, which can work up to liquid nitrogen temperature (77 K). This model is easy to fabricate, low cost, more efficient with less wastage in terms of liquid gases than other models. This model can be used for both low temperature dependent electrical conductivity at ambient pressure and clamped high pressure measurements within the given range

Impact ionization coefficients of 4H- and 6H-SiC

The Monte Carlo (MC) simulation of electron and hole impact ionization rates for 4H- and 6H-SiC in high electric field is presented. This work focuses on the study of impact ionization rates and impact ionization coefficients since these parameters play a very important role in determining the device performance. In our simulation, the impact ionization rates are obtained by using modified Keldysh equation with a softness factor fitted to the experimental data described by other researchers. The electron and hole impact ionization coefficients in 4H- and 6H-SiC are parameterized at high electric field. The electron and hole impact ionization coefficients for a wide range of electric fields have been successfully derived in our model.

Electrical properties of thin films deposited with MnO- and MnO2-modified BiFeO3 oxide targets

Mn-modified Bi1.05FeO3 thin films were deposited on Pt(111)/Ti/SiO2/Si(100) substrates by using a pulsed laser deposition method with BFO oxide targets modified with MnO or MnO2, and the effects of the Mn were investigated. The 3% MnO-modified BFO thin film capacitor exhibited a large remnant polarization (2P r = 179 µC/cm2) and low leakage currents over a wide electric-field range. However, different leakage current behaviors were observed in the 10% MnO-modified and 10% MnO2-modified BFO thin films. The leakage current mechanism of the 10% MnO-modified BFO thin film was Ohmic conduction while that of the 10% MnO2-modified BFO thin film was related to the oxygen vacancy-associated electrical conductivity.

Monte Carlo transport simulation of velocity undershoot in zinc blende and wurtzite InN

AbstractVelocity undershoot in zinc blende (ZB) and wurtzite (WZ) InN is investigated by ensemble Monte Carlo (EMC) calculation. The results show that velocity undershoot arises from the relatively long energy relaxation time compared with momentum. Monte Carlo transport simulations over wide range of electric fields is presented in the paper. The results show that velocity undershoot impacts the electron transport greatly, compared with velocity overshoot, when the electric field changes quickly with time and space. A comparison study between WZ and ZB InN shows that WZ InN has more advantages in device applications due to its excellent electron transport properties.

OBIC Measurements on Avalanche Diodes in 4H-SiC for the Determination of Impact Ionization Coefficients

Optical Beam Induced Current (OBIC) measurements have been performed on 4H-SiC avalanche diodes with very thin and highly doped avalanche region. The light source used in this study is an Ar-laser with a wavelength of 351 nm which results in a mixed carrier injection. From these measurements, impact ionization coefficients for 4H-SiC have been extracted in the electric field range from 3 to 4.8 MV/cm. In combination with ionization coefficients in our previous paper extracted from diodes with lowly doped avalanche region, we propose a set of parameters of impact ionization coefficients for 4H-SiC, applicable to a wide electric field range.

Investigation of electron mobility in GaAs‐based devices using genetic algorithm

PurposeThe purpose of this work is to study the capability of heuristic algorithms like genetic algorithm to estimate the electron transport parameters of the Gallium Arsenide (GaAs). Also, the paper provides a simple but complete electron mobility model for the GaAs based on the genetic algorithm that can be suitable for use in simulation, optimization and design of GaAs‐based electronic and optoelectronic devices.Design/methodology/approachThe genetic algorithm as a powerful heuristic optimization technique is used to approximate the electron transport parameters during the model development.FindingsThe capability of the model to approximate the electron transport properties of Gallium Arsenide is tested using experimental and Monte Carlo data. Results show that the genetic algorithm based model can provide a reliable estimate of the electron mobility in Gallium Arsenide for a wide range of temperatures, concentrations and electric fields. Based on the obtained results, this paper shows that the genetic algorithm can be a useful tool for the estimation of the transport parameters of semiconductors.Originality/valueFor the first time, the genetic algorithm is used to calculate the electron transport parameters in Gallium Arsenide. A complete electron mobility model for a wide range of temperatures, doping concentrations, compensation ratios and electric fields is developed.

Resonant control of polar molecules in individual sites of an optical lattice.

We study the resonant control of two nonreactive polar molecules in an optical lattice site, focusing on the example of RbCs. Collisional control can be achieved by tuning bound states of the intermolecular dipolar potential by varying the applied electric field or trap frequency. We consider a wide range of electric fields and trapping geometries, showing that a three-dimensional optical lattice allows significantly wider avoided crossings than free space or quasi-two dimensional geometries. Furthermore, we find that dipolar confinement-induced resonances can be created with reasonable trapping frequencies and electric fields, and have widths that will enable useful control in forthcoming experiments.

Pyroelectric waste heat energy harvesting using relaxor ferroelectric 8/65/35 PLZT and the Olsen cycle

Waste heat can be directly converted into electrical energy by performing the Olsen cycle on pyroelectric materials. The Olsen cycle consists of two isothermal and two isoelectric field processes in the electric displacement versus electric field diagram. This paper reports on the electrical energy generated by lanthanum-doped lead zirconate titanate (8/65/35 PLZT) subjected to the Olsen cycle. The material was alternately dipped into a cold and a hot silicone oil bath under specified electric fields. A maximum energy density of 888 J l−1/cycle was obtained with a 290 µm thick 8/65/35 PLZT sample for temperatures between 25 and 160 °C and electric fields cycled between 0.2 and 7.5 MV m−1. To the best of our knowledge, this is the largest pyroelectric energy density experimentally measured with multiple cycles. It corresponded to a power density of 15.8 W l−1. The electrical breakdown strength and therefore the energy and power densities of the material increased as the sample thickness was reduced from 720 to 290 µm. Furthermore, a physical model for estimating the energy harvested by ferroelectric relaxors was further validated against experimental data for a wide range of electric fields and temperatures.

Charge Transport in a Highly Phosphorescent Iridium(III) Complex‐Cored Dendrimer with Double Dendrons

AbstractThe charge transporting properties of a phosphorescent iridium(III) complex‐cored dendrimer, with two dendrons attached to each ligand of the core are reported. The results show that the high photoluminescence quantum yield of this material is obtained without compromising charge transport. The hole mobility values are reported over a wide range of temperatures and electric fields using the charge‐generation layer time‐of‐flight technique. The results are analysed using the Gaussian disorder model (GDM), the correlated disorder model, the polaronic correlated disorder model, and the short‐range correlated Gaussian disorder model. It is found that the GDM model gives the most comprehensive description of hole transport in this material. In spite of its larger size, the hole mobility of the doubly dendronised material compares favourably with that of a smaller singly dendronised material, and its spherical shape leads to low energetic disorder and clearly non‐dispersive charge transport. This shows how molecular shape can be used to combine favourable photoluminescence and charge‐transporting properties.

Magnetoelectric properties of Mn-substituted BiFeO3 thin films with a TiO2 barrier

Multiferroic thin films with the general formula TiO2/BiFe1−xMnxO3 (x=0.00, 0.05, 0.10 and 0.15) (TiO2/BFMO) were synthesized on Au/Ti/SiO2/Si substrates using a chemical solution deposition (CSD) method assisted with magnetron sputtering. X-ray diffraction analysis shows the thin films contained perovskite structures with random orientations. Compared with BFMO films, the leakage current density of the TiO2/BFMO thin films was found to be lower by nearly two orders of magnitude, and the remnant polarizations were increased by nearly ten times. The enhanced ferroelectric properties may be attributed to the lower leakage current caused by the introduction of the TiO2 layer. The J–E characteristics indicated that the main conduction mechanism for the TiO2/BFMO thin film was trap-free Ohmic conduction over a wide range of electric fields (0–500kV/cm). In addition, ferromagnetism was observed in the Mn doped BFO thin films at room temperature. The origin of ferromagnetism is related to the competition between distortion of structure and decrease of grain size and decreasing net magnetic moment in films due to Mn doping.

An Analytic Model for Electron Mobility in Strained Si/Si&lt;sub&gt;1-x&lt;/sub&gt;Ge&lt;sub&gt;x&lt;/sub&gt; nMOSFETs

In order to describe electron transport properties in inversion layer of strained Si/Si1-xGex nMOSFETs, a new analytic electron mobility model is proposed. The model not only takes into account the effect of germanium(Ge) content on phonon scattering-limited mobility and surface roughness-limited mobility, and but also includes the degradation effect of strained Si film thickness and temperature on the device mobility. For various Ge content and a wide range of normal electric field, temperature and strained Si film thickness, the model provides good agreement with the experimental data in references. In addition, the model can be expressed using the analytical expression and can be easily included in the device simulator.

Experimental investigation on the effect of top electrode diameter in PZT thick films

We report the effect of top electrode diameter size in aerosol deposited Pb(Zr 0.52Ti 0.48)O 3 thick films (~ 10 μm-thick) with Pt top and bottom electrode. Dielectric and ferroelectric results showed that top electrode diameter of 0.5–1 mm provides reasonable performance with 1 mm being the most suitable dimension in wide range of AC electric field and frequency. The results were discussed based on the surface microstructure and Debye relaxation. The dielectric analysis showed that the properties variation was mainly due to average grain size and defect density. Debye relaxation modeling exhibited that the result is because of materials characteristic not measurement artifact. We believe the results of this study will find immediate application in design of aerosol deposition process.

Novel design for drift tubes in ion mobility spectrometry for optimised resolution of peak clusters

In the past decade, Ion Mobility Spectrometry has established a very strong foot hold in medical and biological applications due to its numerous advantages including sensitivity, ruggedness and reproducibility. During the analysis of complex samples such as human breath, it is very probable that two or more analytes form peak clusters due to similar drift times and pre-separation times, thus hindering the identification of the analytes. Furthermore, such overlapping of signal makes quantification very difficult or even impossible. Resolving these peak clusters is important to enable proper identification and quantification of analytes detected for diagnosis. Hence, we designed a drift tube with variable length for investigating the influence of varying drift lengths and electric field on resolution. Peak cluster formations usually seen between acetone and the reactant ion peak, between the dimer peaks of 2-Heptanone and 4-Heptanone have been resolved with the new drift tube after optimisation. These novel drift tubes could easily negate the peak clusters often encountered when complex medical and biological samples are measured with the ion mobility spectrometer. Furthermore, the fact that these drift tubes can be altered in length thereby providing a wide range of electric fields (from 50 to 3300 V.cm−1), opens up new research options in ion motions in an electric field.

Direct observation of the 1/E dependence of time dependent dielectric breakdown in the presence of copper

Time dependent dielectric breakdown (TDDB) lifetime model study has been performed on a metal-insulator-semiconductor capacitor structure with copper directly deposited on silicon dioxide without a barrier material. The structure generates a low electric field acceleration of time-to-failure, which makes it possible to measure TDDB over a wide range of electric fields from 3.5 to 10 MV/cm and experimentally validate TDDB lifetime model without any assumption and data extrapolation. The experimental results are in good agreement with the so called 1/E model and do not support the E, √E, or power-law model.

Nearly Universal $\hbox{1}/f^{2}$ Spectrum of Mobility Fluctuation Noise in a Quantum Wire at Radio and Microwave Frequencies

We have studied the noise power spectrum associated with mobility fluctuations of hot carriers in a GaAs quantum wire in the frequency range of 20 MHz-50 GHz using ensemble Monte Carlo simulation. This frequency range is outside the regime where a noise peak occurs in quantum wires due to well-known streaming oscillations in the carrier drift velocity. In this frequency range, the noise power spectrum is found to exhibit a nearly universal 1/ <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</i> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">α</sup> dependence, where <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</i> is the frequency. The exponent α remains remarkably constant over a wide range of electric field and temperature, and varies between 1.96 and 1.98 as the driving electric field is varied from 500 V/cm to 10 kV/cm at two different temperatures of 30 and 77 K. The constancy of α and its value of ~ 2 may be related to the nature of electron-phonon interactions in quantum wires.