Mechanism Of Current Flow Research Articles

Features of current flow in the n-CoFe2O4/n-CdTe heterojunction

n-CoFe2O4/n-CdTe heterojunctions with a current rectification ratio of 3·105 at voltages |V| = 1.5 V were made by spray pyrolysis of aqueous solutions of cobalt and iron salts on n-CdTe substrates. Based on the analysis of the temperature dependence of I-V-characteristics in the forward voltage range, a change in the mechanisms of current flow in n-CoFe2O4/n-CdTe heterojunctions was established from overbarrier at voltages of 3kT/q < V < 0.3 V to tunneling at voltages of 0.4 V < V < 1 V. The role of surface states in the formation of the energy profile of the heterojunction and the participation of energy levels in the band gap of n-CdTe in the formation of the tunnel current have been clarified. The reasons for the occurrence of negative differential resistance at the forward biases of the structure have been clarified. The current at reverse biases in the range −3 V < V < -3kT/q was analyzed. According to the analysis of the C-V-characteristics, an inversion layer was found in the heterojunction and its behavior from voltage was explained.

Importance of tides and winds in influencing the nonstationary behaviour of coastal currents in offshore Singapore

Abstract. Coastal currents significantly impact port activities, coastal landform morphodynamics, and ecosystem functioning. It is therefore necessary to understand the physical characteristics and natural variability of these currents within coastal settings. Traditional methods, such as harmonic analysis, assume stationarity of tide-driven currents and may thus not be applicable to systems modulated by variable nontidal inputs and processes. Here we deployed eight tilt current meters in shallow (&lt; 5 m) coral reef environments in southern Singapore. Tilt current meters were positioned around the reefs at the main compass bearings to analyse the spatiotemporal variability of coastal currents in the frequency domain for 1 year (March 2018 to March 2019). Tidal motions were the primary mechanism of current flow on reefs and account for between 14 % and 45 % of total variance across all sites, with diurnal currents having either a similar or greater proportion of energy compared to semidiurnal currents. The relationship between currents and wind stress was then investigated across various frequencies. There is high correlation at low frequencies during the northeast monsoon, when the Madden–Julian Oscillation (MJO) is more active, thus generating currents that propagate either in phase or ahead of the MJO. At diurnal frequencies, the interaction between P1 and K1 results in a semi-annual cycle where currents are stronger during the monsoon seasons. This interaction could help to explain the seasonal variation in correlation as well as the K1 amplitude, the latter of which could be further enhanced by the diurnal wind stress. The phase relationship between currents and wind stress is highly complex due to the variable bathymetry and could only be partially accounted for by the orientation of the coastlines relative to that of the wind. Given the importance of wind, we thus require longer time-series datasets to examine the role of atmospheric phenomena at greater timescales to improve our understanding of the variability of coastal currents.

On the relationship between electrical and electro-optical characteristics in vertical cavity surface emitting lasers for chip scale Rb atomic clocks

We report on a comprehensive study of the electrical and electro-optical properties of 795 nm vertical cavity surface emitting lasers (VCSELs) designed for chip scale Rb atomic clocks. We highlight several key findings including the observation that the current flow at moderate bias levels comprises several parallel paths which are identified by an analysis of the I−V characteristic also confirmed by a numerical simulation. Resistance is a key parameter in any VCSEL. We analyze it in detail at all bias levels and find that above transparency, when the VCSEL enters the high injection regime, the current flow mechanism is modified significantly from an exponential to a power law characteristic. Consequently, resistance attains a nonlinear contribution which is quadratic in the spontaneous emission regime and quasi-linear above the threshold. This nonlinear contribution is not considered in common models. The optoelectronic properties are strongly correlated with the electrical characteristics what allow to explain several peculiarities of the VCSEL performance. We designed and fabricated the VCSELs according to the requirements of miniature Rb atomic clocks, including optimal operation at high temperatures. Their minimum threshold occurs at 363 K where they emit at 794.7 nm. The modal and polarization discrimination in the bias range where these VCSELs operate in practical miniature atomic clocks is well above 30 dB.

Temporary changes in current flow mechanisms in erbium-doped porous silicon

The paper discusses the basic mechanisms of conductivity in silicon MIS structures. The object of the study is porous silicon doped with an erbium impurity of an aqueous solution of erbium nitrate Er(NO3)3 • 5H2O by temperature annealing in a diffusion furnace at a temperature of 800°C for 1 hour. Comparative characteristics of the current-voltage and capacitance-voltage dependences are presented, describing the regular changes in the mechanisms of current flow and charge capture in the samples under study. The results of the work qualitatively and quantitatively describe the temporary change in the electrical characteristics of porous silicon, which can be taken into account by technologists for better understanding the mechanisms of current transfer in luminescent structures of porous silicon with erbium ions, as well as in the study and manufacture of light-emitting diodes based on it.

DC current–voltage and impedance spectroscopy characterization of nCdS/pZnTe HJ

This paper describes the electrical and dielectric behavior of the nCdS/pZnTe HJ by current–voltage, capacitance–voltage characteristics, and impedance spectroscopy in a temperature interval 220–350 K. A microcrystalline p-ZnTe layer and n-CdS were grown on glass/ZnO substrate by closed space sublimation method. As frontal contact to CdS, the transparent ZnO and as a back contact to ZnTe, silver conductive paste (Ag) treated at 50 °C in vacuum were used. The current–voltage results of nCdS/pZnTe HJ show a rectifying behavior. The junction ideality factor, barrier height, and series resistance values were extracted from the rectifying curves at different temperatures. The built-in voltage, carrier concentration and depletion width were obtained from the capacitance–voltage measurements. Analysis of the J–V–T and C–V–T characteristics shows that the thermionic emission and recombination current flow mechanisms dominate in the nCdS/pZnTe HJ. The dielectric study reveals that the experimental values of the AC conductivity, dielectric constant, dielectric loss, the imaginary part of the electric modulus are found to be very sensitive to frequency and temperature. The dielectric constant and dielectric loss are observed to be high at the low frequency region. The increase in the values of electric modulus with the frequency implies an increase in the interfacial polarization at the interface of nCdS/pZnTe HJ. Jonscher’s universal power law shows that with increasing frequency, AC conductivity increased. The results conductivity show that the ionic conductivity and interfacial polarization are the main parameters affecting the dielectric properties of the device when the temperature changes.

The Mechanism of Current Flow in Composite Alumochromiun Ceramics during Its Electron Beam Sintering in a Forevacuum

The Mechanism of Current Flow in Composite Alumochromiun Ceramics during Its Electron Beam Sintering in a Forevacuum

Temporary Changes of Current Flow Mechanisms in Erbium-Doped Porous Silicon

Temporary Changes of Current Flow Mechanisms in Erbium-Doped Porous Silicon

A study of the effect of γ-radiation on the current-carrying mechanism in the P-CuTlS2 single crystal

The electrical conductivity and volt–ampere characteristics (VAC) of the p-CuTlS2 single crystal with specific resistance [Formula: see text] and irradiated by [Formula: see text]-quantum were studied in the range of 100–300[Formula: see text]K temperature and 10–104[Formula: see text]V/cm. It was determined that the cause of the conduction disorder observed in the CuTlS2 single crystal at low electric fields and high radiation doses is the formation of defect clusters dominated by cation vacancies. A sharp increase in current at high electric fields and temperatures occurs as a result of thermo-field ionization of the acceptor level with activation energy [Formula: see text][Formula: see text]eV and the ionization voltage decreases with increasing radiation dose. Based on the determination of the parameters ([Formula: see text]) that determine the mechanism of current flow, the dependence of the shape of the potential hole on the radiation dose was determined.

Current invariant as fundamental relation between saturation currents and band gaps for semiconductor solar cells

The optimization of present multijunction junction solar cells and the development of new concepts is an important task for modem photovoltaics. For its development, special attention should be paid to the potential quality of photoactive p-n junctions, as well as to their properties when operating at various temperatures. The present research has shown that for two-diode model of the p-n junction it is convenient to use current invariants Jz1 and Jz2 for calculating the diffusion and recombination saturation dark currents J01 and J02 for p-n junctions based on semiconductor materials with any band-gap energy. It has been experimentally found that Jz1 and Jz2 are constants relating the semiconductor material band gap energy and temperature with J01 and J02. It has also been shown that Jz1 and Jz2 determine the open circuit voltage and the value of voltage offset WOC. Current invariant suggested to be useful tool for evaluating the quality of a p-n junction and for modeling the characteristics of solar cells because it allows making calculations taking into account both main mechanisms of current flow and the operating temperature of the device.

Electrical Properties of Anisotype ZnO:Al/n-ZnSe/p-CdTe Heterostructures.

ZnO:Al/n-ZnSe/p-CdTe anisotype heterostructures with diode properties were fabricated by the high-frequency magnetron deposition of ZnO:Al and n-ZnSe thin films onto the surface of crystalline p-CdTe. The flow of currents limited by the space charge at forward voltages up to 0.45 V and tunneling currents at V > 0.45 V was established. A change in these current flow mechanisms was observed at reverse voltages V = -0.6 V. The main part of the energy barrier qϕk = 1 eV of the ZnO:Al/n-ZnSe/p-CdTe heterostructure was formed in the p-CdTe substrate, which was established from studies of capacitance-voltage (C-V) characteristics. A model of the energy diagram of the heterostructure is proposed.

Low temperature electrical transport in thin carbon films deposited on SiO2/Si substrates by pulsed laser deposition

In this paper electrical transport studies are performed on thin carbon films deposited on SiO2/Si substrates by pulsed laser deposition (PLD) applying laser ablation of micro-crystalline graphite target. Experiments were carried out on 320 - 420 nm thick SiO2 on Si substrates as well as on hydrogenated diamond-like carbon (DLC) films deposited on SiO2/Si. Structural studies by means of XPS, SEM and Raman spectroscopy revealed that the films can be characterized as nano-sized carbon phases possessing different phase composition (i.e. the ratio sp3/sp2 hybridized carbon, etc.). The electrical conductivity/resistivity of the films was measured in the temperature range 10 K < T < 300 K. Four-contact Van der Pauw method as well as two contact schemes have been applied. Some films have low room temperature resistivity in the range ρ = (0.1–1.5)×10-3 Ω.·m and consist predominantly of sp2 hybridized carbon with Raman spectra, which resemble that of nano-sized graphene depending on the deposition conditions and substrates used. The thinnest only 0.5 nm layer deposited directly on SiO2 exhibits relatively low specific resistance (~10-3 Ω. m), which can be taken as an indication of good deposition conditions of graphene-like layers. The current flow mechanism was explored at temperatures from 300 K down to 10K. The temperature dependence reveals non-metallic behavior - the conductivity decreases at decreasing temperature as opposed to typical metal behaviour. A model of variable range hopping (VRH) mechanism is applied to explain the low temperature conductivity drawn from transport in nanocrystalline disordered systems.

Low temperature electrical transport in microwave plasma fabricated free-standing graphene and N-graphene sheets

In this paper, the electrical transport in free-standing graphene and N-graphene sheets fabricated by a microwave plasma-based method is addressed. Temperature–dependent resistivity/conductivity measurements are performed on the graphene/N-graphene sheets compressed in pellets. Different measurement configurations reveal directional dependence of current flow—the room-temperature conductivity longitudinal to the pellet’s plane is an order of magnitude higher than the transversal one, due to the preferential orientation of graphene sheets in the pellets. SEM imaging confirms that the graphene sheets are mostly oriented parallel to the pellet’s plane and stacked in agglomerates. The high longitudinal electrical conductivity with values on the order of 103 S/m should be noted. Further, the current flow mechanism revealed from resistivity-temperature dependences from 300K down to 10K shows non-metallic behavior manifested with an increasing resistivity with decreasing the temperature usually observed for insulating or localized systems. The observed charge transport shows variable range hopping at lower temperatures and thermally activated behaviour at higher temperatures. This allows us to attribute the charge transport mechanism to a partially disordered system in which single graphene sheets are placed predominantly parallel to each other and stacked together.

The mechanism of current flow in composite alumochromiun ceramics during its electron beam sintering in a forevacuum

It is shown that during electron beam sintering in the forevacuum pressure region of powder components of composite Al2O3-Cr ceramics, the magnitude of the current flowing through the sample depends both on the percentage of chromium and on the heating temperature of the sample. When a certain temperature is reached, the process of current flow is influenced by thermoelectric emission from the sample surface. Along with the ions from the beam plasma, a noticeable thermoelectric emission current contributes to the process of neutralizing the charging of the ceramic surface with an electron beam and reduces the absolute value of the negative potential of the sample surface. This ultimately contributes to an increase in the efficiency of energy transfer from the electron beam to the sample. Keywords: Electron beam irradiation of oxide ceramics, electrical conductivity, alumina ceramics, chromium, composite, electron beam, forevacuum.

Determining the mechanisms of current flow in structures of two-layer dielectrics

Diodes of type Metal-Dielectric 1-Dielectric 2-Metal are promising for use in devices paired with antennas-rectennas. To create diodes with the characteristics required for operation, it is necessary to understand the mechanisms of current transport in both dielectrics and their contacts with metals. To solve this problem, it is necessary to develop an algorithm for dividing the general current-voltage characteristic into characteristics of individual contacts, the analysis of which will also allow us to investigate the problems of the properties of defects in the dielectrics that make up the diode. In this paper, the solution of the above problems is presented on the example of the Al-Al2O3-Ta2O5-Ni diode. The authors showed how one can divide the current-voltage characteristic into components, calculate potential barriers at the boundaries of metals with contacting dielectrics, and determine the concentration and energy characteristics of structural defects in dielectrics. Keywords: metal-insulator-metal diodes, current-voltage characteristics, Poole-Frenkel effect, currents of thermionic and thermal field emission, currents limited by space charge.

Исследования радиационной стойкости гетероструктурных кремниевых солнечных элементов

The radiation resistance of different types of heterostructural silicon solar cells under irradiation with 1 MeV electrons in the fluence range 2.5•1014 - 1•1015 cm-2 has been studied. Studies have shown that the smallest degradation of the“saturation” currents of the diffusion current flow mechanism from J0d ≤ 5 10-13 to J0d ≤ 3 10-12 A/cm2 and efficiency from 19.2 to 13.6% (AM0, 1367W/m2) were n-α-Si:H/c-p(Ga)/p-α-Si:H and n-µc-Si:H/c-p(Ga)/p-α-Si:H. The results obtained make it possible to evaluate the prospects for the use of heterostructure silicon solar cells for low-orbit spacecraft.

Simulation based studies on performance of SiC temperature sensors

Present work reports the simulation based analysis of SiC temperature sensors based on schottky diode within temperature limit from 100 K to 400 K. The forward bias characteristics of Ni/SiC Schottky diode are simulated using Silvaco TCAD software. The variation in on-voltage with temperature has been extracted and plotted on the basis of current voltage features of forward bias. Thereafter the sensitivity of the designed structure has been determined and plotted as function of measurement current levels. It was found that device works well in the mentioned temperature range which attests its suitability in harsh environments. The findings of the work have been described in terms of thermionic emission current flow mechanism in the device.

Dark conduction mechanisms of PTQBDT based heterojunction diode

Al:LiF/PTQBT:PCBM/PEDOT:PSS/ITO/glass organic-based diode is fabricated with different weight ratios in PTQBT:PCBM active layer. The diodes D1, D2 and D3 are prepared using the precursor solution for spin coating process as 1:2, 1:3 and 1:4, respectively. Under dark, main diode parameters are extracted by conventional thermionic emission theory using the results of measurements. Parasitic resistance contribution, non-ideal barrier height formation and high values of ideality factor indicate possible effects of space charge limited current flow mechanism on forward biased characteristics. At saturated voltage region, series resistances are calculated and the results are evaluated according to Cheung’s method. The possible voltage sharing between interface layer and depletion region are also investigated by analysis of density of interface states. In addition, field effect is found in a major role on the reverse current flow and the mechanism is evaluated according to Schottky-Richardson model.

Investigating Gate Interface Traps in β-Ga2O3 Field Effect Transistors (MOSFETs) By Using the Transfer Length Method (TLM) and UV Exposure

Beta-gallium oxide (β-Ga2O3) is a promising ultra-wide bandgap semiconductor for high power electronic applications due to its high theoretical critical field of 8 MV/cm, and Baliga figure of merit (BFOM) of ~3300, 3 – 10 times larger than current state-of-the-art wide bandgap semiconductors. β-Ga2O3 field-effect transistors (FETs) have been explored for both high power and radio frequency (RF) operation, but with relatively high parasitic resistances. A method is developed to determine the contact, series, and channel resistances in depletion mode β-Ga2O3 MOSFETs. The Al2O3-β-Ga2O3 interface is primarily important in the performance of β-Ga2O3 FETs due to charge trapping. Measurements will be performed with UV and visible light radiation to study the role of trap states on the FET resistances and device performance.Here, we report on using a modified transfer length method (TLM) to determine the contact, series, and channel resistances from planar, depletion-mode β-Ga2O3 FETs. The results are compared with respect to conventional TLM structures fabricated on the same wafer. The β-Ga2O3 FETs and TLM structures are fabricated on a (010) semi-insulating β-Ga2O3 substrate. The channel layer is a 50 nm Si-doped epi-layer with a target concentration of 2.4 x 1018 cm-3. A Ti/Al/Ni/Au metal stack is deposited and annealed to form Ohmic contacts. The gate dielectric is composed of atomic layer deposition-grown aluminum oxide (Al2O3, 20 nm). The structures have a constant gate length, LG, of 1.94 μm, while the total source-drain spacing, LSD, varies as 3μm, 8 μm, and 13 μm. Transfer characteristics were measured at room temperature and low drain-source voltage, VDS, of 0.01 V. The threshold voltage, VTH, was determined to be » -4V for all MOSFET devices. Measurements were performed in the dark or under UV (265 nm, 2.8 W/cm2) exposure.Conventional TLM structures were measured in the dark and with UV exposure, and a 40% decrease in the sheet resistance was observed when exposed to UV. We attribute this change to an increase in the carrier concentration from photo-generated electrons due to trap states within the β-Ga2O3. We also performed I-V measurements of the FETs in the dark and observed hysteresis behavior with respect to gate-source voltage, VGS, which we attribute to trapped charge at the Al2O3-β-Ga2O3 interface. Using the TLM method, we developed a methodology to extract the β-Ga2O3 MOSFET channel sheet resistances within the gated (Rsh,G) and ungated (Rsh) regions as a function of VGS. We observe a significant decrease in Rsh,G from 288 ± 14 kΩ sq-1 to 7.6 ± 0.38 kΩ sq-1 as VGS varies from -3 V to 3 V. The sheet resistance in the ungated regions, Rsh, shows a negligible change from 28 ± 1.4 kΩ sq-1 above a VGS of -1.8 V, comparable to that of the conventional TLM structures, but begins to increase with more negative VGS, reaching 90 ± 4.5 kΩ sq-1 at a VGS of -3 V. The VGS dependence of Rsh is due to complicated current flow mechanisms when the depletion region is large, which is not considered in this model. We will extend the study by performing I-V measurements with UV and visible light radiation to observe any effect of traps at the Al2O3-β-Ga2O3 interface has on Rsh and Rsh,G.

Flexibility of fluorinated graphene based memristor structures: current flow model in a multi-barrier system under tensile strain

The flexibility of two types of memristor structures with fluorinated graphene (FG) based active layers (FG with graphene islands on polyvinyl alcohol, FG/PVA, and films from nanoparticles of V2O5 capsulated with FG, FG/V2O5) under the tensile strain in bending conditions was investigated and compared in the present study. Both types of memristors show a similar mechanism of resistance switchings (current paths on traps without filaments). Multi-barrier model of current flow was used to estimate the barrier parameters connected to FG from experiments on resistive switching of memristor structures in the bending condition. The first type of structures (Ag/FG/PVA/Ag) demonstrates the record high values of flexibility: ON/OFF current relation is not changed up to 7% tensile strain created by bending. The second type of structures (Gr/FG/V2O5/Gr with graphene contacts) show a decrease in ON current already for tensile strain more than 2%. The similar mechanism of current flow allows us to use the similar theory for description of the current flow versus the tensile strain. In spite of different structures and morphology of memristors, the typical values of the barrier height extracted from the theoretical description were similar: ∼1.5 eV with an effective barrier thickness of ∼16.5 nm and ∼1.3–1.6 eV with thickness 13.5–15.0 nm for FG/PVA and FG/V2O5 structures, respectively. Increase in the barrier thickness over 19 nm in both cases leads to the strong decrease in ON current of memristors.

Trench Split Gate MOSFET’s Inductive Switching

A trench split gate metal-oxide-semiconductor field-effect transistor (MOSFET) inductive switching is analyzed by adopting six-terminal method. Owing to the buried source terminal in the trench oxide, conventional three-terminal (gate, source, and drain) analysis has a limitation for investigating the detailed time-dependent current flow in the drift region, channel, as well as each terminal. However, a mixed-mode simulation tools enable us to look into the complicated current flow mechanisms in the device by dividing the gate terminal into the gate-to-source and the gate-to-drain terminals and the source terminal into the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${n} +$ </tex-math></inline-formula> , the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${p} +$ </tex-math></inline-formula> , and the shielded source terminals. The six-terminal method enables us to understand the fundamental turn-on and turn-off switching mechanisms that we have not found out so far from the measurement.