Temperature Current-voltage Characteristics Research Articles

ZrxCo0.8−xNi0.2−xFe2O4-graphene nanocomposite for enhanced structural, dielectric and visible light photocatalytic applications

Zirconium doped nickel cobalt ferrite (ZrxCo0.8−xNi0.2−xFe2O4) nanoparticles and ZrxCo0.8−xNi0.2−xFe2O4-graphene nanocomposites were synthesized by a cheap and facile co-precipitation method. Annealing was done at 750°C for 6.5h. Spinel cubic structure of prepared nanoparticles was confirmed by X-ray powder diffraction (XRD) technique. Crystalline size of nanoparticles was observed in the range of 18–27nm. Graphene was synthesized by Hummer's method. Formation of rGO was confirmed by UV-visible spectroscopy (UV-vis) and XRD. ZrxCo0.8−xNi0.2−xFe2O4-graphene nanocomposites were prepared by ultra-sonication route. Grain size of nanoparticles and dispersion of nanoparticles between rGO layers was determined by Scanning electron microscopy (SEM). In application studies of nanoparticles and their nanocomposites, photocatalytic efficiency of nanoparticles under visible light irradiation was observed by degradation of methylene blue. Charge transfer resistance was measured by electrochemical impedance spectroscopy (EIS) and the variation in dc electrical resistivity was analyzed by room temperature current voltage characteristics (I-V). Dielectric constant was also evaluated in frequency range from 1MHz to 3GHz. All these investigations confirmed the possible utilization of these materials for a variety of applications such as visible light photocatalysis, high frequency devices fabrication etc.

Resistance switching memory characteristics of CaF2/Si/CaF2 resonant-tunneling quantum-well heterostructures sandwiched by nanocrystalline Si secondary barrier layers

A novel resistance switching memory using CaF2/Si/CaF2 resonant-tunneling quantum well heterostructures sandwiched by nanocrystalline Si (nc-Si) as secondary barrier layers has been proposed and the room temperature current–voltage characteristics of the basic resistance switching memory operation have been demonstrated. A resistance switching voltage of 1.0 V, a peak current density of approximately 42 kA/cm2, and an ON/OFF ratio of 2.8 were observed. In particular, more than 28000 write-read-erase cyclic memory operations have been demonstrated by applying pulsed input voltage sequences, which suggests better endurance than the device using a CaF2/CdF2/CaF2 heterostructure.

Electrical transport in transverse direction through silicon carbon alloy multilayers containing regular size silicon quantum dots

Electrical transport in the transverse direction has been studied through a series of hydrogenated silicon carbon alloy multilayers (SiC-MLs) deposited by plasma enhanced chemical vapor deposition method. Each SiC-ML consists of 30 cycles of the alternating layers of a nearly amorphous silicon carbide (a-SiC:H) and a microcrystalline silicon carbide (μc-SiC:H) that contains high density of silicon quantum dots (Si-QDs). A detailed investigation by cross sectional TEM reveals preferential growth of densely packed Si-QDs of regular sizes ∼4.8nm in diameter in a vertically aligned columnar structure within the SiC-ML. More than six orders of magnitude increase in transverse current through the SiC-ML structure were observed for decrease in the a-SiC:H layer thickness from 13nm to 2nm. The electrical transport mechanism was established to be a combination of grain boundary or band tail hopping and Frenkel–Poole (F-P) type conduction depending on the temperature and externally applied voltage ranges. Evaluation of trap concentration within the multilayer structures from the fitted room temperature current voltage characteristics by F-P function shows reduction up-to two orders of magnitude indicating an improvement in the short range order in the a-SiC:H matrix for decrease in the thickness of a-SiC:H layer.

Simulations of Graphene Base Transistors With Improved Graphene Interface Model

A simulation study of the graphene base heterojunction transistor (GBHT) is presented based on a novel realistic graphene–Si interface model, calibrated on the experimental graphene–Si Schottky diodes, whose current–voltage-temperature characteristics are well reproduced. The GBHT simulations predict $f_{T}$ in the tens-of-gigahertz range and confirm the need for an improved quality of the graphene interface for the terahertz operation to be reached.

Tailoring phase slip events through magnetic doping in superconductor-ferromagnet composite films.

The interplay between superconductivity (SC) and ferromagnetism (FM) when embedded together has attracted unprecedented research interest due to very rare coexistence of these two phenomena. The focus has been mainly put into the proximity induced effects like, coexistence of magnetism and superconductivity, higher critical current, triplet superconductivity etc. However, very little attention has been paid experimentally to the role of magnetic constituent on triggering phase slip processes in the composite films (CFs). We demonstrate that less than 1 at.% of magnetic contribution in the CFs can initiate phase slip events efficiently. Due to advanced state-of-the-art fabrication techniques, phase slip based studies have been concentrated mainly on superconducting nanostructures. Here, we employ wide mesoscopic NbGd based CFs to study the phase slip processes. Low temperature current-voltage characteristics (IVCs) of CFs show stair-like features originated through phase slip events and are absent in pure SC films. Depending on the bias current and temperature, distinct regions, dominated by Abrikosov type vortex-antivortex (v-av) pairs and phase slip events, are observed. The results presented here open a new way to study the phase slip mechanism, its interaction with v-av pairs in two dimensions and hence can be useful for future photonic and metrological applications.

High temperature current-voltage characteristics of InP-based tunnel junctions

In this paper, we present temperature-dependent current–voltage measurements of tunnel junctions lattice matched to InP at temperatures ranging from room temperature to 220 °C. Temperature-dependent tunneling properties were extracted by fitting the current–voltage characteristics using a simple analytical formula. Three different designs of tunnel junction were characterized, including a bulk InAlGaAs tunnel junction, an InAlGaAs tunnel junction with InAlAs cladding layers and an InGaAs/InAlGaAs quantum-well tunnel junction. Each device exhibited different temperature dependence in peak tunnel current and excess current, with the quantum-well tunnel junction exhibiting the greatest temperature sensitivity. We use a non-local tunneling model, in conjunction with a numerical drift-diffusion solver, to explain the performance improvement available by using double heterostructure cladding layers around the junction region, and use the same model to explain the observed temperature dependence of the devices. Copyright © 2014 John Wiley & Sons, Ltd.

Current–voltage–temperature characteristics and magnetic response of Co/n-CuO/p-Si/Al heterojunction diode

Cupric oxide (CuO) films with n-type conductivity and polycrystalline structure were successfully synthesized onto p-Si substrates by simple thermal oxidation of copper films prepared by liquid phase epitaxy (LPE) technique. Scanning electron microscope showed that the films consist of spherical particles with a diameter in the range of 0.5–0.67µm. The dark current-voltage characteristics of Co/n-CuO/p-Si/Al diode were investigated in temperature range 300–390K. The ideality factor and barrier height were determined in terms of thermionic emission theory. Norde's function was used for determining the barrier height and series resistance. At relatively higher applied voltage, space charge limited current dominated by exponential trap of distribution is the operating conduction mechanism. The Co/CuO/p-Si multilayers showed ferromagnetic response in which the coercivity and saturation magnetization are evaluated.

Performance characteristics of CdTe drift ring detector

CdTe and CdZnTe material is an excellent candidate for the fabrication of high energy X-ray spectroscopic detectors due to their good quantum efficiency and room temperature operation. The main material limitation is associated with the poor charge transport properties of holes. The motivation of this work is to investigate the performance characteristics of a detector fabricated with a drift ring geometry that is insensitive to the transport of holes. The performance of a prototype Ohmic CdTe drift ring detector fabricated by Acrorad with 3 drift rings is reported; measurements include room temperature current voltage characteristics (IV) and spectroscopic performance. The data shows that the energy resolution of the detector is limited by leakage current which is a combination of bulk and surface leakage currents. The energy resolution was studied as a function of incident X-ray position with an X-ray microbeam at the Diamond Light Source. Different ring biasing schemes were investigated and the results show that by increasing the lateral field (i.e. the bias gradient across the rings) the active area, evaluated by the detected count rate, increased significantly.

Ultraviolet Photodetection Properties of ZnO/Si Heterojunction Diodes Fabricated by ALD Technique Without Using a Buffer Layer

The fabrication and characterization of a Si/ZnO thin film heterojunction ultraviolet photodiode has been presented in this paper. ZnO thin film of ~100 nm thick was deposited on <100> Silicon (Si) wafer by atomic layer deposition (ALD) technique. The Photoluminescence spectroscopy confirms that as-deposited ZnO thin film has excellent visible-blind UV response with almost no defects in the visible region. The room temperature current-voltage characteristics of the n-ZnO thin film/p-Si photodiodes are measured under an UV illumination of 650 <W at 365 nm in the applied voltage range of ±2V. The current-voltage characteristics demonstrate an excellent UV photoresponse of the device in its reverse bias operation with a contrast ratio of ~ 1115 and responsivity of ~0.075 A/W at 2 V reverse bias voltage.

Composition-dependent metal-insulator transition in perovskite CaXPb(1−X) TiO3 (CPT) ceramic

Ceramic compositions of a complex perovskite CaXPb(1−X)TiO3 (CPT) systems with x=0.6, 0.7 and 0.8 were prepared by mechanical mixing of their oxides (CaTiO3 and PbTiO3). The structure of the (CPT) ceramics was characterized by X-ray diffraction (XRD) The ceramics transform gradually from orthorhombic phase (pseudo cubic phase) to cubic phase by increasing pb content percent. The dc resistivity ρ(t) versus temperature (range 300–525K) for x=0.6, 0.7 and 0.8. The ρ.T/curves reveal that samples exhibit a metallic behaviour at low temperature and undergo a metal-semiconductor transition with increasing temperature at Tp=373K, 343K and 333K, for x=0.6, 0.7 and 0.8, respectively. The nature of conduction mechanism is studied in semiconductor region by studying the current–voltage temperature characteristics. The current–voltage characteristics were interpreted in terms of Poole–Frenkel type of conduction mechanism.

Characterization of deep levels in n-type and semi-insulating 4H-SiC epitaxial layers by thermally stimulated current spectroscopy

We have investigated deep level centers in n-type and semi-insulating (SI) 4H-SiC epitaxial layers by thermally stimulated current (TSC) spectroscopy. The epitaxial layers were grown using chemical vapor deposition utilizing a dichlorosilane precursor. Both epitaxial layers exhibited relatively shallow levels related to Al, B, L- and D-centers. A deep level center with an activation energy of 1.1 eV, peaked at ∼400 K, was detected in the n-type epitaxial layer and correlated with the IL2 level and the 1.1 eV center in a high purity bulk SI 4H-SiC. The TSC spectra of the SI epitaxial layer was dominated by the peaks at 525–585 K that we attributed to intrinsic defects and their complexes with energy levels close to the middle of the bandgap. The TSC spectra of SI epitaxial layer exhibited peaks with different current polarity which is explained by thermoelectric effect and the built-in electric field reversal. The results of the transfer length method measurements of the SI epitaxial layer and the room temperature current-voltage (I-V) characteristics of both epitaxial layers are also reported.

Temperature Dependence of the Giant Magnetoresistance in Fe/DNA/Fe Structure

A numerical study is presented to investigate the spin-dependent transport through poly(dG)-poly(dC) DNA molecule sandwiched between ferromagnetic contacts in the absence and in the presence of environmental effects. Making use of tight-binding procedure and within the framework of a generalized Green's function technique, the room temperature current-voltage characteristics of DNA molecule and the giant magnetoresistance (GMR) of Electrode/DNA/Electrode structure, with iron (Fe) as the electrode are studied. It is found that the GMR to be lower than 12% for small applied bias and about 35% for applied bias larger than 2.5 volts. Considering the environmental effects, the GMR would be increased up to 13% at a bias lower than 2 volts and decreases up to 23% for the bias about 2.5 volts. In addition, our calculations indicate that for applied biases around 2.5 volts, the GMR decreases when the temperature increased.

Hydrothermal synthesis of CdTe QDs: Their luminescence quenching in the presence of bio-molecules and observation of bistable memory effect in CdTe QD/PEDOT:PSS heterostructure

We report one-pot hydrothermal synthesis of nearly mono-disperse 3-mercaptopropionic acid capped water-soluble cadmium telluride (CdTe) quantum dots (QDs) using an air stable Te source. The optical and electrical characteristics were also studied here. It was shown that the hydrothermal synthesis could be tuned to synthesize nano structures of uniform size close to nanometers. The emissions of the CdTe QDs thus synthesized were in the range of 500–700 nm by varying the duration of synthesis. The full width at half maximum (FWHM) of the emission peaks is relatively narrow (40–90 nm), which indicates a nearly uniform distribution of QD size. The structural and optical properties of the QDs were characterized by transmission electron microscopy (TEM), photoluminescence (PL) and Ultraviolet–visible (UV–Vis) spectroscopy. The photoluminescence quenching of CdTe QDs in the presence of l-cysteine and DNA confirms its biocompatibility and its utility for biosensing applications. The room temperature current–voltage characteristics of QD film on ITO coated glass substrate show an electrically induced switching between states with high and low conductivities. The phenomenon is explained on the basis of charge confinement in quantum dots.

Sensor properties of structures with porous silicon layer

We have measured at room temperature current-voltage and noise characteristics of structures with a porous silicon (porosity 80%) layer at adsorption of gases ammonia, propane and butane mixture, and ethyl alcohol vapor. It was obtained that the largest change in CVC and low-frequency noise is observed under action of ammonia gas on the structure. Physical reasons of sensor properties of studied samples are discussed.

Characterization of InGaN/GaN light-emitting diodes with micro-hole arrayed indium-tin-oxide layer

We demonstrate that InGaN/GaN multiple quantum well light-emitting diodes (LEDs) with micro-hole arrayed indium-tin-oxide layers exhibit better performance and optoelectrical properties than do conventional LEDs. Under 20 mA injection current operation the room-temperature output power conversion efficiency and external quantum efficiency obtained by employing a micro-hole array on the top surface of the LED structure could be increased by 28.7% and 14.3%, respectively, over that of conventional broad area devices. The room temperature current–voltage characteristics of the LEDs showed the series resistance and leakage current to be related to the hole dimensions and etching depth, respectively. Interestingly, the leakage current of the transparent conductive layer was dominated by the contribution of the micro-hole side-wall, the number of etched micro-holes, and the wet-etching depth. We conclude that a well-designed micro-hole array structure fabricated using the wet etching process can indeed, not only significantly inhibit the leakage current of the indium-tin-oxide transparent conductive layer, but also enhance the external quantum efficiency and extraction efficiency over a broad temperature range.

TMR and spin-dependent transport of polyacetylene-based magnetic junctions

A numerical study is presented that investigates the spin-dependent transport through a trans-polyacetylene (trans-PA) molecule sandwiched between ferromagnetic (FM) contacts. Using the tight-binding procedure and in the framework of a generalized Green's function technique, the room temperature current–voltage characteristics of the trans-PA molecule and the tunnel magnetoresistance (TMR) of the electrode/trans-PA/electrode structure, with iron (Fe) as the electrode, are studied. It is found that the parallel arrangement of magnetic moments in FM electrodes causes a much higher current through the polyacetylene molecule than does the anti-parallel arrangement. Also, our results indicate that TMR has its maximum value (more than 60%) at low bias voltages.

The current–voltage–temperature characteristics of Al/NPB/p-Si contact

The current–voltage ( I– V) characteristics of the Al/NPB/p-Si contact shows rectifying behavior with a potential barrier formed at the contact interface. The barrier height and ideality factor values of 0.65 eV and 1.33 are measured at the forward bias of the diode. The barrier height of the Al/NPB/p-Si diode at room temperature is larger that (∼0.58 eV) of conventional Al/p-Si diode. It reveals the NPB organic film control the carrier transport of the diode at the contact interface. The temperature effect on the I– V measurement is also performed to reveal the junction characteristics. The ideality factor of the Al/NPB/p-Si contact increases with decreasing temperature. And the barrier height decreases with decreasing temperature. The effects are due to the existence of the interface states and the inhomogeneous of the barrier at the junction.

Si Esaki diodes with high peak to valley current ratios

We report room temperature current voltage characteristics of Si p+-i-n+ Esaki diodes integrated on silicon substrates. The diodes were fabricated by low-temperature molecular beam epitaxy. Very high and abrupt p- and n-type dopant transitions into the 1020 cm−3 ranges are achieved by boron and antimony, respectively. The integrated devices are realized without a postgrowth annealing step. The silicon Esaki diodes show negative differential resistance at room temperature with excellent peak to valley current ratios up to 3.94. A variation in the thickness of the silicon tunneling barrier changes the peak current density over three orders of magnitude.

Antimony doped Si Esaki diodes without post growth annealing

Room temperature current density versus voltage characteristics of silicon Esaki diodes grown with molecular beam epitaxy are presented. The diodes are doped with boron and antimony. The integrated devices are realized without a post growth annealing step. Good peak to valley current ratios in excess of 3 and excellent peak current densities up to 5.2 kA/cm 2 were found at room temperature. We present a detailed investigation of the influence on the boron surface segregation effects of the peak current density.

Synthesis and characterization of conducting polypyrrole-polymannuronate nanocomposites

Polypyrrole-polymannuronate (PPy-PM) composite films were studied by preparing the composites via in situ deposition techniques. These studies on the chemical interactions, structural morphology, and thermal properties of the films support the formation of PPy-PM composites, and suggest that the ratio of pyrrole to PM is tailored to optimize the potential crosslinking inside the composite. The room temperature current–voltage characteristics and the frequency-dependent AC conductivity of the PPy-PM composites were studied within the frequency range of 102 to 106 Hz. Based on the aforementioned properties, the synthesis of PPy-PM composite films may suggest the future development of biomimetic materials that can be used to create new multicomponent and multifunctional bionanocomposite materials.