Current-Voltage Characteristic

We model charge transport in disordered semiconducting polymers by hopping of charge carriers on a square lattice of sites with Gaussian on-site energy disorder, using Fermi-Dirac statistics. From numerically exact solutions of the Master equation, we study the dependence of the charge-carrier mobility on temperature, carrier density, and electric field. Our results are used in calculating current-voltage characteristics of hole-only polymer diodes. It is found that very good fits to experimental current-voltage characteristics can be obtained at different temperatures, with reasonable fitting parameters for the width of the Gaussian density of states and the lattice constant. In agreement with the experiments we find that the density dependence is dominant over the field dependence. Only at high fields and low temperatures the field dependence becomes noticeable. The potential and current distribution show strong inhomogeneities, which may have important consequences for the operation of polymer opto-electronic devices.

Thin films of charge-ordered Nd0.5Ca0.5MnO3, Y0.5Ca0.5MnO3, and Nd0.5Sr0.5MnO3 have been prepared on Si(100) and LaAlO3(100) substrates by the nebulized spray pyrolysis of organometallic precursors. Small electric fields induce insulator–metal transitions in the films with the resistivity decreasing with increasing current. The current–voltage characteristics are non-ohmic and show some hysteresis. The current-induced negative differential resistance found in these manganate films could have potential technological applications.

Until recently, in experimental fusion devices only cold probes were used to determine the plasma potential, and their floating potential was assumed to be proportional to the plasma potential. However, drifting electrons or beams distort the current-voltage characteristic of a cold probe. In addition a cold probe is sensitive to electron temperature variations. These problems can be avoided by the use of electron emissive probes, since an electron emission current is fairly independent of the conditions in the surrounding plasma. We have used an emissive probe in the CASTOR tokamak in Prague, by which the plasma potential has been determined in the edge region of this device and even inside in last closed flux surface (LCFS). In this paper we present first results of our investigations.

Until recently, in experimental fusion devices only cold probes were used to determine the plasma potential, and their floating potential was assumed to be proportional to the plasma potential. However, drifting electrons or beams distort the current-voltage characteristic of a cold probe. In addition a cold probe is sensitive to electron temperature variations. These problems can be avoided by the use of electron emissive probes, since an electron emission current is fairly independent of the conditions in the surrounding plasma. We have used an emissive probe in the CASTOR tokamak in Prague, by which the plasma potential has been determined in the edge region of this device and even inside in last closed flux surface (LCFS). In this paper we present first results of our investigations.

We use a simple nonlinear Kronig-Penney model to study multistability and discontinuity in the current- voltage characteristics of doped semiconductor superlattices in a homogeneous electric field. Nonlinearity in our model enters through a self-consistent potential used to describe the interaction of the effective electrons with charge accumulation in the doped layers. We show that the process of Wannier-Stark localization is slowed down by the nonlinear effect in the doped layers, and that the shrinking and destruction of minibands in the superlattice by the nonlinearity is related to the occurrence of discontinuity and multistability in the transport of electrons.

Methane is a potent greenhouse gas, significantly contributing to global warming gases when released into the atmosphere. Methane, a naturally occurring gas, has no harmful impacts on human life at low concentrations. As concentrations rise, symptoms like fatigue, headaches, nausea, irritability, and speech difficulties increase due to asphyxiation. Zinc oxide (ZnO) and graphene-doped ZnO gas sensors were fabricated using a screen-printing technique onto a Kapton film to compare their performance to methane gas at room temperature. A silver paste was used as the interdigitated electrode, deposited on the Kapton film using a screen-printing technique, and fired at 150 °C for 15 minutes. Next, ZnO and graphene-doped ZnO pastes were deposited onto the interdigitated electrode using a screen-printing technique and became the second layer of the gas sensor. The sensing layer was annealed at 200 °C for 60 minutes. All gas sensors responded well to methane gas at room temperature. As a comparison, the graphene-doped ZnO gas sensor responded better to 6,700 ppm of methane gas than the ZnO gas sensor at room temperature. The highest response of graphene-doped ZnO to methane gas was produced by 5 wt. % of graphene doped into ZnO with a response value of 11.5.

A resonant tunneling diode, GaAs/In x Ga 1-x As/Al y Ga 1-y As/GaAs/Al 0.3 Ga 0.7 As/GaAs was studied under laser field. The effect of the pre-well potential In x Ga 1-x As on the current voltage characteristics was examined depending on the indium concentration. It has been observed that the current-voltage characteristic exhibits a critical value if the depth of the pre-well increased by increasing indium concentration. The electrons are accelerated for shallow pre-wells before that critical value and decelerated for deeper pre-wells than that of the critical value potential. In addition, the current is decreased increasing the width of the GaAs central well. The performance of the devices can be changed by applying a laser field when the geometric parameters are adjusted in resonant tunneling diodes.

IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 46, NO. 11, NOVEMBER 1999 ... Steady-State and Transient Forward Current–Voltage ... Diodes at High and Superhigh Current Densities ... Nina V. Dyakonova, Pavel A. Ivanov, Vladimir A. Kozlov, ME Levinshtein, ...
Steady-state and transient forward current-voltage I-V characteristics have been measured in 5.5 kV p+-n-n⁺ 4H-SiC rectifier diodes up to a current density j&ap;5.5×10 4 A/cm2. The steady-state data are compared with calculations in the framework of a model, in which the emitter injection coefficient decreases with increasing current density. To compare correctly the experimental and theoretical results, the lifetime of minority carriers for high injection level, τph, has been estimated from transient characteristics. At low injection level, the hole diffusion length Lpl has been measured by photoresponse technique. For a low-doped n-base, the hole diffusion lengths are Lpl&ap;2 μm and Lph&ap;6-10 μm at low and high injection levels respectively. Hole lifetimes for low and high injection levels are τpl&ap;15 ns and τph&ap;140-400 ns. The calculated and experimental results agree well within the wide range of current densities 10 A/cm 2<j< 4×103 A/cm2. At j>5 kA/cm2, the experimental values of residual voltage drop V is lower than the calculated ones. In the range of current densities 5×103 A/cm2<j<2×104 A/cm2, the minimal value of differential resistance R_d=dV/dj is 1.5×10-4 Ω cm2. At j>25 kA/cm2, Rd increases with increasing current density manifesting the contribution of other nonlinear mechanisms to the formation steady-state current-voltage characteristic. The possible role of Auger recombination is also discussed

A new double integration-based method to extract model parameters is applied to experimental polysilicon nanowire MOSFETs. The threshold voltage and Subthreshold Slope factor are extracted from noisy measured current-voltage characteristics. It is shown that the present method offers advantages over previous extraction procedures regarding data noise reduction. In addition, the normalized mutual integral difference operator method is scrutinized and an improvement of the method is presented.

We present a microscopic theory of bipolar quantum well structures in the photovoltaic regime, based on the non-equilibrium Green's function formalism for a multi band tight binding Hamiltonian. The quantum kinetic equations for the single particle Green's functions of electrons and holes are selfconsistently coupled to Poisson's equation, including inter-carrier scattering on the Hartree level. Relaxation and broadening mechanisms are considered by the inclusion of acoustic and optical electron-phonon interaction in a self consistent Born approximation of the scattering self energies. Photogeneration of carriers is described on the same level in terms of a self energy derived from the standard dipole approximation of the electron-photon interaction. Results from a simple two band model are shown for the local density of states, spectral response, current spectrum, and current-voltage characteristics for generic single quantum well systems.

We present a microscopic theory of bipolar quantum well structures in the photovoltaic regime, based on the non-equilibrium Green's function formalism for a multi band tight binding Hamiltonian. The quantum kinetic equations for the single particle Green's functions of electrons and holes are selfconsistently coupled to Poisson's equation, including inter-carrier scattering on the Hartree level. Relaxation and broadening mechanisms are considered by the inclusion of acoustic and optical electron-phonon interaction in a self consistent Born approximation of the scattering self energies. Photogeneration of carriers is described on the same level in terms of a self energy derived from the standard dipole approximation of the electron-photon interaction. Results from a simple two band model are shown for the local density of states, spectral response, current spectrum, and current-voltage characteristics for generic single quantum well systems.

An analysis of the accurateness of determining the plasma space potential from the probe current-voltage characteristics have been performed to improve the accurateness of the consequently determining plasma parameters from it. The problem is analyzed as an inverse and ill-posed one. Tikhonov&#x27;s regularization method was introduced to solve such problem. It was shown that the accurate determination of the plasma potential is the most important for low temperature plasma &lt;1 eV. The method was checked in argon plasma created in the double plasma machine. The satisfactory results were obtained.

Reported here is the fabrication of 20–100nm channel length pentacene field-effect transistors (FETs) with well-behaved current-voltage characteristics. Using a solution deposition method, pentacene grains span entire devices, providing superior contacts. Varying the gate oxide thickness, the effects of scaling on transistor performance is studied. When the channel length to oxide thickness exceeds 5:1, electrostatically well-scaled nanometer FETs are prepared. The results show that the device characteristics are dominated by the contacts. Decreasing the oxide thickness lowers the device turn-on voltage beyond simple field scaling, as sharper bending of the gate potential lines around the contacts more effectively reduces the molecule/source interfacial resistance.

We have fabricated and characterized at low temperature, down to 0.32 K, tunnel junctions made by a thin film of heavily doped silicon in contact with superconducting electrodes through Schottky barriers. Doped silicon films were chemical vapor deposited on silicon-on-insulator substrates and laterally dry etched in mesas. Aluminum or, alternatively, niobium contacts were deposited on the mesas. Below the superconducting critical temperature Tc, an energy gap opens in the superconductor and the current–voltage characteristics become nonlinear and strongly sensitive to temperature changes. We have also characterized the heavily doped silicon in terms of the electron–phonon thermal decoupling by cooling the electron gas by means of aluminum–silicon–aluminum structures. With Nb electrodes, we have observed an anomaly of the electrical differential conductance at zero voltage and a larger electron dissipation, as a result of a less opaque barrier.