Current Conduction Model Research Articles

Resistive switching behaviour of nickel nanoparticle-embedded naphthalene sulphonic acid-doped polyaniline nanocomposites

Hybrid nanocomposite (NC) materials comprising organic polymers and inorganic metal nanoparticles (NPs) with unique properties are popular for their advanced technological applications including resistive switching memory devices. Herein, NCs of 2-naphthalene sulphonic acid-doped polyaniline nanotubes (PANI-NSA NTs) and nickel nanoparticles (Ni NPs) were synthesized via a facile chemical synthesis procedure where metallic Ni NPs were embedded in/deposited onto the surface of PANI-NSA NTs by a simple reduction method. Different characterization methods revealed successful deposition of weak ferromagnetic Ni NPs onto the PANI-NSA matrix. The bipolar resistive switching behaviour of the as-synthesized PANI-NSA + Ni NCs was investigated under the application of voltage stress in a two-terminal sandwiched device configuration. The fabricated indium tin oxide/PANI-NSA + Ni/silver (ITO/PANI-NSA + Ni/Ag) device displays bipolar resistive switching properties having a memory window of ∼1.5 × 103, and switches effectively over 200 cycles. Ohmic conduction in the lower-voltage regime and the space-charge-limited Mott–Gurney current conduction model in the higher-voltage region were identified as major charge conduction mechanisms in the high resistive state of the device. On the other hand, in the entire low resistive state region the experimental data followed the Mott–Gurney conduction model.

Resistive switching effect in RE-Doped cobalt ferrite nanoparticles

Spinel ferrite along with numerous important properties, also exhibit resistive switching effect. Cerium (Ce) doped Co-ferrite nanoparticles having composition CoFe2-xCexO4 (where x = 0.0, 0.05, 0.15, 0.20) were synthesized by co-precipitation synthesis route. X-ray Diffraction analysis confirmed the formation of cubic spinel phase with minor amount of impurities. Frequency dependent dielectric and electrical properties were studied at room temperature within frequency range of 20 Hz to 3 MHz. Dielectric constant, dielectric losses and AC conductivity decreases with cerium substitutions which is usual trend observed in ferrite materials. Modified Debye function was employed to fit Dielectric constant (ε′)- frequency (f) data. Jonscher's power law was employed to study AC conductivity. DC resistivity decreased with increasing temperature. DC resistivity and drift mobility decreased with cerium substitution while activation energy increased. Current–Voltage (I–V) curves of the synthesized composition were studied at room temperature. Current–Voltage (I–V) curves showed nonlinear hysteresis loop like behavior. Current follow different values for forward and reversed applied DC voltage which confirmed that resistive switching effect exit in studied samples. Sample with Ce composition x = 0.25 exhibit larger hysteresis loop than that of other compositions. This shows that sample for Ce composition x = 0.25, can be employed for nonvolatile Resistive Random-Access Memory (ReRAM) applications. Resistive switching effect was explained by utilizing Space-charge-limited current (SCLC) conduction model and by formation of a Schottky barrier at the metal-semiconductor interface.

Analysis and Modeling of Vertical Current Conduction and Breakdown Mechanisms in Semi-Insulating GaN Grown on GaN: Role of Deep Levels

Vertical current conduction in a 1.3- μm-thick semi-insulating (SI) C-doped GaN grown on a GaN substrate is analyzed. During the growth, pressure was varied from 100 to 20 mbar in order to increase C concentration from ~ 1×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">17</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> to ~ 6×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">18</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> ; SI GaN is sandwiched between two n-GaN layers. Optical transitions suggest two acceptor levels: ~0.9 eV above the valence band and ~0.6 eV below the conduction band. Current-voltage characterizations reveal a space-charge-limited-current conduction with an impact-ionization-assisted filling of traps in a moderately C-doped sample. On the other hand, highly compensated SI GaN forms a ~0.5-eV potential barrier at the interface with n-GaN, whereas the breakdown voltage exceeds 350 V. As the model explains, deep acceptors above the valence band compensate residual donors and lead to an electron mobility collapse. On the other hand, depending on C concentration, acceptors below the conduction band play a different role. In the moderately doped SI GaN, they act as electron traps and define the breakdown voltage. On the other hand, acceptors below the conduction band in highly compensated SI GaN are responsible for the barrier-controlled conduction and reaching of the avalanche.

Bipolar resistive switching and non-volatile memory properties of MnO2-polyaniline (PANI) nanocomposite

Organic materials are becoming a promising candidate for non-volatile memory especially resistive switching memories. The present work reports bipolar resistive switching and memristive properties of polyaniline coated MnO2 nanocomposite. The hybrid nanocomposite was synthesized by oxidative polymerization of aniline in the presence of the MnO2 nanostructures. The XRD analysis confirms the α-MnO2 phase and the TEM micrograph reveals the formation of nanorods of the material. The results of Attenuated Total Reflection Infrared Spectroscopy (ATR-IR) and Thermogravimetric analysis (TGA) confirmed the presence of the polymer in the composite. The developed device shows bipolar resistive switching behavior with a memory window ~7 × 102, switches efficiently over 103 cycles, and can retain the data over 104 seconds. Space charge limited current conduction model along with the possible filamentary route of operation describes conduction and resistive switching mechanisms of the device.

Investigation of electrical parameters of Au/P3HT:PCBM/n-6H–SiC/Ag Schottky barrier diode with different current conduction models

Abstract We have researched the electrical characteristics of Au/P3HT:PCBM/n-6H–SiC/Ag Schottky barrier diode (SBD) fabricated with a polymer interface layer between 300 and 375 K temperatures. The experimentally obtained parameters from current-voltage (I–V) measurements are calculated with four different current conduction models. It is observed that parameters calculated from research findings related to different methods are compatible with each other. The barrier inhomogeneity of the metal-polymer-semiconductor (MPS) interface layer is explained by Gaussian distribution (GD). Furthermore, the mean barrier height ( Ф ‾ bo) and the modified effective Richardson constant (A**) are found by drawing Richardson curves of the sample. Finally, the electrical properties of Au/P3HT:PCBM/n-6H–SiC/Ag SBD have been determined to affect the interface materials and the interface state density (Nss) as well as the current conduction models.

Observation of Different Charge Transport Processes and Origin of Magnetism in rGO and rGO-ZnSe Composite

The effect of nanoparticle incorporation inside reduced graphene oxide (rGO) layers on the electrical transport properties has been investigated by temperature-dependent resistivity measurements on rGO and rGO-zinc selenide (rGO-ZnSe) thin films in a wide temperature range of 84–473 K. The fraction of ZnSe in rGO-ZnSe composite has been varied from 26 to 98%. Resistance curve derivative analysis reveals a conduction mechanism consistent with Mott two-dimensional (2D) variable range hopping (VRH) in rGO films, whereas different rGO-ZnSe samples exhibit three-dimensional (3D) VRH at lower temperatures (84–280 K). At higher temperatures (290–473 K), Arrhenius-like transport was observed for all of the samples. A model where ZnSe nanoparticles are incorporated inside wrinkled rGO layers to facilitate interlayer connections, thus 3D charge transport, has been proposed. Room-temperature carrier mobility values, calculated using trap-free space charge limited current conduction model in the dark, reach a maximum...

Non-volatile resistive switching in oxide ion conductor BiYO3 thin films

We experimentally demonstrate non-volatile resistive switching (RS) with a resistance window of ∼10× in oxide ion conductor BiYO3 (BYO) thin films. (111)-oriented BYO films of multiple thicknesses (20 nm–300 nm) were deposited using the pulsed laser deposition technique on a Pt/TiO2/SiO2/Si substrate. The thermal stability of BYO films in a wide temperature range (10 K–800 K) was confirmed, using temperature dependent dielectric measurements. Further, impedance spectroscopy suggests the presence of oxygen vacancies (defects) at the Au/BYO interface in the high resistance state (after forming) too. Root mean square roughness of the films varied from 1.16 nm to 2.76 nm, confirming a uniform and homogeneous surface. We explain the conduction mechanism in our Au/BYO/Pt devices using space charge limited current (SCLC) and Ohmic conduction models. The bipolar RS characteristics of the BYO devices are empirically modeled on the basis of the oxygen ion driven filamentary switching process.

Analytic Modeling of Nonlinear Current Conduction in Access Regions of III-Nitride HEMTs

AbstractThe transconductance degradation caused by the non-linear resistance of access regions in III-nitride high electron-mobility transistors (HEMTs) is mainly responsible for limiting the RF linearity of the transistor. In this paper, we use Landauer’s transmission theory to develop an analytic electrothermal current-voltage (I-V) model of access regions in III-nitride HEMTs. With only 12 parameters, most of which have a physical origin and can be obtained through experimental calibration, the model is able to correctly predict the I-V behavior in access regions from the drift-diffusive to the quasi-ballistic transport regimes. Model accuracy is demonstrated by comparing the results against experimental and numerical hydrodynamic simulations of ungated transmission line structures with length scales ranging from few 10’s of nanometers to 10’s of micrometers.

Effects of coarse aggregates on the electrical resistivity of Portland cement concrete

Electrical resistivity of concrete is an inherent material parameter associated with the composition, condition, and deterioration of concrete. Over the past few decades, studies have focused on the applicability of employing concrete resistivity as a self-monitoring indicator. This study attempted to investigate the effects of coarse aggregates (CAs) on the electrical resistivity of Portland cement concrete. Concrete mixtures with variations in CA content, size, and type were designed under identical water to cement ratios and curing conditions, and tested at 28days. Bulk resistivity (BR) was measured using two-probe methods under saturated surface dry (SSD) conditions. Backscattered electron images (BEI) obtained using scanning electron microscopes (SEM) and X-ray computed tomography (CT) image analysis were also employed to study the capillary porosities and mesoscale voids that might affect BR. A mesoscale current conduction model was also employed for interpretation. The experimental results suggested that concrete resistivity is sensitive to the inclusion of CAs. Instead of altering the cement hydration, CAs were observed to serve as direct electrical obstacles that resulted in the enhancement of BR. Higher CA content increased the existence of obstacles, thereby increasing BR. Variations in CA size and type were observed to exert no effects on BR, which further validated the adopted mesoscale current conduction model, and further indicated that interfacial transition zones do not exert a substantial influence on concrete resistivity. It was also observed that capillary porosities and mesoscale voids were not influenced by CA content, indicating that cement pastes had similar quality among all concrete mixtures.

Highly dense and textured superconducting (Bi,Pb)2Sr2Ca2Cu3O10+δ ceramic samples processed by spark-plasma texturing

Consolidated powders of the superconducting cuprate Bi1.65Pb0.35Sr2Ca2Cu3O10+δ (Bi-2223) by the spark-plasma texturing (SPT), spark-plasma sintering (SPS), and the traditional solid-state reaction method were investigated by several techniques and their features compared. The results show that SPT samples exhibit a higher degree of texture, as inferred by a Lotgering factor of ∼0.73 along the [00l] direction and a relative density of 96% of the theoretical value. From magnetic hysteresis loops M vs. H at 5K, the intragranular critical current densities along two applied magnetic field orientations, Jc0c and Jc0ab, relative to the compacting pressure direction, were determined. The anisotropy factor, γJ=Jc0ab/Jc0c, yielded an estimate of ∼2 in the SPS sample and ∼19 for samples obtained via the SPT method. In the latter samples, Jc0c at 5K is close to 1.3×108A/cm2, a value higher than others found for the same compound. The temperature dependence of the electrical resistivity, ρ(T), analyzed within the framework of a current conduction model for granular superconductors, supports the higher degree of texture of SPT samples and indicates changes in the oxygen content when samples are subjected to a post-annealing heat treatment. All the results reveal the promising capabilities of the SPT method for improving volume density, texture, and grain boundary connectivity of superconducting Bi-2223 materials.

Effect of CuPc layer insertion on the memory performance of CdS nanocomposite diodes

In the present work, semiconductor diodes with CdS nanocomposite as an active layer have been fabricated and investigated for memory device applications. The effect of copper phthalocyanine (CuPc) layer insertion between the bottom electrode and CdS nanocomposite has been studied. I–V characteristics show electrical hysteresis behaviour vital for memory storage application. The as-fabricated devices exhibit bipolar switching behaviour with OFF to ON state transition at positive bias and vice versa. Device with CuPc layer exhibits ION/IOFF ratio ̃ 1.4 × 104. Possible conduction mechanism has been described on the basis of theoretical current conduction models. The frequency dispersion capacitance, series resistance and conductance of the devices have been studied and discussed. At low frequency, the series resistance and the interface states dominate the electrical properties of the device. The results indicate that the multilayered devices open up the possibility of new generation non-volatile memory devices with low cost, high density and stability.

Space-charge-controlled field emission model of current conduction through Al2O3 films

This study proposes a model for current conduction in metal-insulator-semiconductor (MIS) capacitors, assuming the presence of two sheets of charge in the insulator, and derives analytical formulae of field emission (FE) currents under both negative and positive bias. Since it is affected by the space charge in the insulator, this particular FE differs from the conventional FE and is accordingly named the space-charge-controlled (SCC) FE. The gate insulator of this study was a stack of atomic-layer-deposition Al2O3 and underlying chemical SiO2 formed on Si substrates. The current-voltage (I-V) characteristics simulated using the SCC-FE formulae quantitatively reproduced the experimental results obtained by measuring Au- and Al-gated Al2O3/SiO2 MIS capacitors under both biases. The two sheets of charge in the Al2O3 films were estimated to be positive and located at a depth of greater than 4 nm from the Al2O3/SiO2 interface and less than 2 nm from the gate. The density of the former is approximately 1 × 1013 cm−2 in units of electronic charge, regardless of the type of capacitor. The latter forms a sheet of dipoles together with image charges in the gate and hence causes potential jumps of 0.4 V and 1.1 V in the Au- and Al-gated capacitors, respectively. Within a margin of error, this sheet of dipoles is ideally located at the gate/Al2O3 interface and effectively reduces the work function of the gate by the magnitude of the potential jumps mentioned above. These facts indicate that the currents in the Al2O3/SiO2 MIS capacitors are enhanced as compared to those in ideal capacitors and that the currents in the Al-gated capacitors under negative bias (electron emission from the gate) are more markedly enhanced than those in the Au-gated capacitors. The larger number of gate-side dipoles in the Al-gated capacitors is possibly caused by the reaction between the Al and Al2O3, and therefore gate materials that do not react with underlying gate insulators should be chosen in order to achieve a low leakage current by suppressing the current enhancement. Although the current conduction in this study is essentially limited by FE, neither the Fowler-Nordheim (FN) nor Poole-Frenkel (PF) plots of the I-V characteristics are fitted by a linear function. The failures of the FN and PF plot methods alert us to the inaccuracies of basing the investigation of current conduction on these traditional plots. Hence, the methodology of a current conduction analysis and the knowledge of Al2O3 charging in this study provide a solid foundation for investigating the current conduction in MIS capacitors.

Microstructural characterization and current conduction mechanisms of front-side contact of n-type crystalline Si solar cells with Ag/Al pastes

Recently, high efficiency n-type crystalline Si cells made with the screen printed Ag/Al metallization have received considerable attention. We report here our microstructural investigations of the critical interfacial region between the front-side contact and the Si wafer of n-type cells fired under progressively higher temperatures. Our study revealed that the key characteristic microstructures of the interfacial region changed from one with a large fraction of residual SiNx, to one consisting of a thin glass layer with nano-Ag colloids, and finally to one decorated with Ag and Ag/Al crystallites attached to the emitter surface for cells with under-, optimally-, and over-fired conditions, respectively. We did not find any Al-Si eutectic layer on the emitter surface that would support a silicon dissolution and re-growth mechanism, which is operative in the back surface field formation process for the Al back contact of p-type industrial solar cells. The presence of the SiNx antireflection coating has likely altered the chemistry between Si and Al significantly. The observed microstructures lead us to conclude that the main current conduction mechanism in optimally-fired n-type cells is tunneling through those areas of thin interfacial glass containing nano-Ag colloids. This mechanism is similar to the current conduction model we have proposed previously for optimally-fired p-type crystalline Si solar cells. We believe that the intrusion of Ag/Al (and/or Ag) crystallites into the p+-Si emitter in over-fired cells is one of the major sources of metallization-induced recombination losses, which degrades cell performance.

Current Conduction Mechanism of Front-Side Contact of N-Type Crystalline Si Solar Cells With Ag/Al Pastes

Recently, n-type crystalline Si (c-Si) cells with front-side (FS) metallization Ag/Al paste have attracted considerable attention. However, a clear understanding of current conduction mechanism is still lacking. We report here the results of our microstructural investigation of the interfacial contact region using electron microscopy techniques. In optimally fired cells, we did not find any Al-Si eutectic layer on the emitter surface that would support a regrowth mechanism as found during the back surface field formation process commonly practiced to create the full plane Al back contact of p-type industrial solar cells. The presence of SiN x antireflection coating has possibly altered significantly the chemistry between Si and Al. The observed microstructures suggest that the current conduction is predominantly tunneling through ultrathin interfacial glass, assisted by the presence of nano-Ag colloids. We believe this mechanism is similar to the current conduction model we have proposed previously for FS Ag-contact of p-type c-Si solar cells with Ag paste.

Current Conduction Model for Oxide-Based Resistive Random Access Memory Verified by Low-Frequency Noise Analysis

A conduction model consisting of two parallel resistances from a highly conductive filament region and a uniform leakage oxide region is proposed in this brief to represent the current conduction in the filament-type switching resistive random access memory cell. Low-frequency noise analysis of current fluctuation at different resistance states has been employed to verify its efficiency. It is found that, in the low-resistance regime, filament resistance dominates current conduction and noise varies as a power law of resistance, whereas in the high-resistance regime, uniform oxide leakage is the major source of conduction, giving rise to a nearly constant noise level.

Carrier Transport Mechanisms of Organic Bistable Devices Fabricated Utilizing Hybrid C60/Poly(methyl methacrylate) Nanocomposites

Organic bistable devices (OBDs) based on nanocomposites consisting of C60 embedded in the poly(methyl methacrylate) (PMMA) layer were fabricated by using a spin coating method. The current density–voltage (J–V) curves of the Al/C60 embedded in PMMA layer/indium–tin-oxide devices exhibited an electrical bistability with a low-conductivity state, a transition state, and a high-conductivity state. The J–V curves for OBDs containing hybrid C60 and PMMA except a low voltage range were reasonably fitted by using the space-charge-limited current conduction model. The trapped electron densities of the OBDs were attributed to the space charge relative to the internal electric field.

Carrier Transport Mechanisms of Organic Bistable Devices Fabricated Utilizing Hybrid C60/Poly(methyl methacrylate) Nanocomposites

Organic bistable devices (OBDs) based on nanocomposites consisting of C60 embedded in the poly(methyl methacrylate) (PMMA) layer were fabricated by using a spin coating method. The current density–voltage (J–V) curves of the Al/C60 embedded in PMMA layer/indium–tin-oxide devices exhibited an electrical bistability with a low-conductivity state, a transition state, and a high-conductivity state. The J–V curves for OBDs containing hybrid C60 and PMMA except a low voltage range were reasonably fitted by using the space-charge-limited current conduction model. The trapped electron densities of the OBDs were attributed to the space charge relative to the internal electric field.

Theory of charging and charge transport in “intermediate” thickness dielectrics and its implications for characterization and reliability

Thin film dielectrics have broad applications, and the performance degradation due to charge trapping in these thin films is an important and pervasive reliability concern. It has been presumed since the 1960s that current transport in intermediate-thickness (IT) oxides (∼10–100 nm) can be described by Frenkel-Poole (FP) conduction (originally developed for ∼mm-thick films) and algorithms based on the FP theory can be used to extract defect energy levels and charging-limited lifetime. In this paper, we review the published results to show that the presumption of FP-dominated current in IT oxides is incorrect, and therefore, the methods to extract trap-depths to predict lifetime should be revised. We generalize/adapt the bulk FP current conduction model by including additional tunneling-based current injection. Steady state characteristics are obtained by a flux balance between contacts and the IT oxide. An analytical approximation of the generalized FP model yields a steady state leakage current J ∝ exp(−B√E)(1 − C√E − D/E), where B, C, and D are material-specific constants. This reformulation provides a new algorithm for extracting defect levels to predict the corresponding charging limited device lifetime. The validity and robustness of the new algorithm are confirmed by simulations and published experimental data.

A Semi-analytical Model for Depletion-mode N-type Nanowire Field-effect Transistor (NWFET) with Top-gate Structure

We propose a semi-analytical current conduction model for depletion-mode n-type nanowire field-effect transistors (NWFETs) with top-gate structure. The NWFET model is based on an equivalent circuit consisting of two back-to-hack Schottky diodes for the metal-semiconductor (MS) contacts and the intrinsic top-gate NWFET. The intrinsic top-gate NWFET model is derived from the current conduction mechanisms due to bulk charges through the center neutral region as well as of accumulation charges through the surface accumulation region, based on the electrostatic method, and thus it includes all current conduction mechanisms of the NWFET operating at various top-gate bias conditions. Our previously developed Schottky diode model is used for the MS contacts. The newly developed model is integrated into ADS, in which the intrinsic part of the NWFET is developed by utilizing the Symbolically Defined Device (SDD) for an equation-based nonlinear model. The results simulated from the newly developed NWFET model reproduce considerably well the reported experimental results.

Temperature Dependence of the Intergranular Critical Current Density in Uniaxially Pressed Bi1.65Pb0.35Sr2Ca2Cu3O10+δ Samples

We have studied the normal and superconducting transport properties of Bi1.65Pb0.35Sr2Ca2Cu3O10+δ (Bi-2223) ceramic samples. Four samples, from the same batch, were prepared by the solid-state reaction method and pressed uniaxially at different compacting pressures, ranging from 90 to 250 MPa before the last heat treatment. From the temperature dependence of the electrical resistivity, combined with current conduction models for cuprates, we were able to separate contributions arising from both the grain misalignment and microstructural defects. The behavior of the critical current density as a function of temperature at zero applied magnetic field, Jc(T), was fitted to the relationship Jc(T)∝(1−T/Tc)n, with n≈ 2 in all samples. We have also investigated the behavior of the product Jcρsr, where ρsr is the specific resistance of the grain-boundary. The results were interpreted by considering the relation between these parameters and the grain-boundary angle, θ, with increasing the uniaxial compacting pressure. We have found that the above type of mechanical deformation improves the alignment of the grains. Consequently the samples exhibit an enhance in the intergranular properties, resulting in a decrease of the specific resistance of the grain-boundary and an increase in the critical current density.