I–V characteristic of electronic transport through a quantum dot chain: The role of antiresonance

The I–V spectrum of electronic transport through a quantum dot chain is calculated by means of the nonequilibrium Green function technique. In such a system, two arbitrary quantum dots are connected with two electron reservoirs through leads. When the dot-lead coupling is very weak, a series of discrete resonant peaks in electron transmission function cause staircase-like I–V characteristic. On the contrary, in the relatively strong dot-lead coupling regime, stairs in the I–V spectrum due to resonance vanish. However, when there are some dangling quantum dots in the chain outside two leads, the antiresonance which corresponds to the zero points of electron transmission function brings about novel staircase characteristic in the I–V spectrum. Moreover, two features in the I–V spectrum arising from the antiresonance are pointed out, which are significant for possible device applications. One is the multiple negative differential conductance regions, and another is regarding to create a highly spin-polarized current through the quantum dot chain by the interplay of the resonance and antiresonance. Finally, we focus on the role that the many-body effect plays on the antiresonance. Our result is that the antiresonance remains when the electron interaction is considered to the second order approximation.     

Intrinsic memory characteristic of polycrystalline ZnTe film originating from Mott variable range hopping conduction

The resistive switching characteristics of Au/ZnTe/ITO structure with polycrystalline ZnTe film as resistive switching layer is investigated. Macroscopically, 100 bipolar switching cycles under the direct current (dc) voltages were carried out and the conduction states can retain for several hours. Microscopically, reading and writing operations can be achieved on ZnTe film with Au top electrode replaced by conductive Atomic Force Microscopy (c-AFM) tip. The I–V characteristic in low resistance state (LRS) is linear in the whole range of voltage. The I–V characteristic in high resistance state (HRS) is linear in the low voltage while it obeys Schottky emission in the high voltage, and Schottky barrier height is symmetric in the positive and negative voltage. During linear I–V characteristic voltage range, the electrons transport between adjacent point defects via Mott variable range hopping. The higher hopping distance and higher activation energy in HRS contribute to the higher resistance value in HRS compared with LRS. Impedance spectroscopy in HRS and LRS both behave as a semicircle, which accords with the semiconductor-like characteristic of conductive point defects. Photoluminescence (PL) spectroscopy indicates the decisive role of deep level defects in conduction. This study confirms the intrinsic resistive switching characteristic of ZnTe film and provides a new choice for intrinsic non-oxides material in nonvolatile memory application.     

Effect of 100 MeV Si7+ ions’ irradiation on Pd/n-GaAs Schottky diodes

Pd/n-GaAs realized devices (junction made on a virgin substrate prior to irradiation) and Pd/n-GaAs fabricated devices (junction realized after the virgin substrate irradiation) have been irradiated with 100?MeV Si⁷⁺ ions for the varying fluence of 10¹²–10^13?ions/cm². The devices have been characterized by I–V and C–V techniques for an electrical response. The electrical characterization of these devices shows the presence of interfacial layer. Moreover, the C–V characteristics show strong frequency dependence behavior, which indicates the involvement of interfacial charge layer with deep electron states. The hydrogenation of these devices has not caused any significant change in the electrical (I–V and C–V) characteristics. The observed results have been discussed in the realm of radiation-induced defects, which cause the carrier removal and compensation phenomena to cause the observed high resistivity and filling and unfilling of these traps’ level to cause strong frequency dependence behavior.     

Critical current behavior of superconducting granular NbN films

The temperature dependence of the critical current I_c(T) below the paracoherent-coherent phase transition T_cj in granular NbN films of high sheet resistance has been measured. Current-voltage (I–V) determinations of I_c revealed two distinctive temperature regions. Above T1, (T1≈ 0.6T_cj), nonlinear, but continuous I–V curves were obtained for I>I_c. Below T1, the voltage discontinously jumped to a finite value at I_c and then increased linearly with current. At T1, a sudden increase in I_c is observed. Small magnetic fields (< 1 mT) suppressed the excess critical current but fields up to 40 mT had minimal further effect. Data suggest that T1 is a characteristic onset temperature associated with an additional ordering in the samples.     

Multisaturation process revealed by brillouin scattering in CdS

Brillouin scattering of light by sound waves in photoconducting CdS under current saturation conditions gives a fair explanation for the multisaturations of the I–V characteristic. The acoustic flux is spread in the symmetry plane ⊥ to the C axis and is made up of on-axis and of-axis shear phonons respectively responsible for the first and second saturation. Off-axis modes are located in privileged directions which depend on the crystal size and surface treatment. D. L. White's theory explains the whole experimental observation and foresees the occurrence of more than two knees in the I–V characteristic.     

Experimental realization of the fuse model of crack formation

In this work, we present an experimental investigation of the fuse model. Our main goal was to study the influence of the disorder on the fracture process. The experimental apparatus used consisted of an L x L square lattice with fuses placed on each bond of the lattice. Two types of materials were used as fuses: copper and steel wool wires. The lattice composed only of copper wires varied from a weakly disordered system to a strongly disordered one. The lattice formed only by steel wool wires corresponded to a strongly disordered one. The experimental procedure consisted of applying a potential difference V to the lattice and measuring the respective current I. The characteristic function I(V) obtained was investigated in order to find the scaling law dependence of the voltage and the current on the system size L when the disorder was changed. Our results show that the scaling laws are only verified for the disordered regime.     

Temperature-Dependent Current–Voltage (I–V) and Capacitance–Voltage (C–V) Characteristics of Ni/Cu/n-InP Schottky Barrier Diodes

The current-voltage (I–V) and capacitance-voltage (C–V) characteristics of Ni/Cu/n-InP Schottky barrier diodes are studied over a wide temperature range, from 210 K to 420 K. The I–V characteristics display anomalous thermal behavior. The apparent barrier height decays, and the ideality factor grows at low temperatures, and the series resistances resulting from Cheung’s and Norde’s procedures are markedly temperature dependent. The nonlinearity of the Richardson plot and the strong temperature dependence of the Schottky-barrier parameters indicate that the interface is spatially inhomogeneous. Plots of the zero-bias barrier height as a function of 1/(2kT) points to a Gaussian distribution of barrier heights with 0.90 eV mean height and 0.014 eV standard deviation. When this distribution is accounted for, a Richardson of 6.5 A/(cm K)² results, relatively close to the 9.4/(cm K)² predicted by theory. We conclude that, combined with a Gaussian distribution of barrier heights, the thermionic-emission mechanism explains the temperature-dependent I–V and C–V characteristics of the studied Schottky-barrier diodes.     

Superconductivity as a consequence of an ordering of the electron gas zero-point oscillations

It is shown that the temperature dependence of the value of energy gap in superconductors is characteristic for the order–disorder transition. The obtained relationship between the critical parameters of the Bose–Einstein condensate of electrically charged particles is in accordance with measurement data of superconductor critical parameters. The dependence of the critical temperatures for both – I and II – type superconductors and their Sommerfeld constants (and their Fermi energies) is obtained. It is marked that among the high-temperature superconducting ceramics there are the both – I and II – type superconductors. In total the phenomenon of superconductivity is seen as a consequence of ordering into the zero-point oscillation system of the electron gas in a metal at low temperatures. The obtained estimations of the interaction of zero-point oscillations are in satisfactory agreement with the data measurements of critical parameters of I and II type superconductors.     

Simulation of a Detector of Visible and Near-IR Electromagnetic Radiation Based on Artificial Diamond

Technical Physics - A method for calculation of the I–V characteristic is proposed for a detector of visible and near-IR electromagnetic radiation based on artificial diamond with allowance...     

Electrical characterization of polymer matrix — TiO2 filler composites through isothermal polarization / depolarization currents and I–V tests

Specimens of polymer matrix — ceramic TiO₂ filler composites were prepared. The contribution of the filler content on the electrical conductivity and energy storage properties of the samples was examined. I–V and Isothermal Polarization/Depolarization Current (IPC/IDC) measurements were conducted. Dc conductivity values directly calculated from the I–V curves exhibited excellent agreement with corresponding values derived from the IPC/IDC recordings. Standard models were employed for fitting the IPC/IDC data. In specific, the short and the very long depolarization times were fitted by use of power laws of different slopes, while the intermediate depolarization times were fitted as a sum of three exponential decays. The present study reveals a strong dependence of the depolarization and polarization processes, as well as of the dc conductivity, on the filler concentration.     

The study of structure and optoelectronic properties of ZnS and ZnO films on porous silicon substrates

ZnS and ZnO films were prepared on porous silicon (PS) substrates with the same porosity by pulsed laser deposition (PLD), and the structural, optical and electrical properties of ZnS and ZnO films on PS were investigated at room temperature by X-ray diffraction (XRD), scanning electron microscope (SEM), optical absorption measurement, photoluminescence (PL) and I–V characteristic studies. The prepared ZnS was obtained in the cubic phase along β-ZnS (1 1 1) orientation which showed a perfect match with the earlier report while ZnO films were obtained in c-axis orientation. There appeared some cracks in the surface of ZnS and ZnO films due to the roughness of PS substrates. Luminescence studies of ZnS/PS and ZnO/PS composites indicated room temperature emission in a broad, intense, visible photoluminescence band, which cover the blue emission to red emission, exhibiting intensively white light emission. Based on the I–V characteristic, ZnS/PS heterojunction exhibited the rectifying junction behavior, while the I–V characteristic of ZnO/PS heterostructure was different from that of the common diode, whose reverse current was not saturated.     

Bias dependence of apparent layer thickness and Moiré pattern on NaCl/Cu(001)

Bias-dependent features of the insulating NaCl layer grown on Cu(001) have been investigated by scanning tunneling microscopy/spectroscopy (STM/STS). The apparent layer thickness of the NaCl film is variable at bias voltages ranging from 2.8 to 3.2 V as well as from 4.0 to 5.0 V, and the Moiré pattern induced by NaCl–Cu lattice mismatch also shows bias dependence. The z–V (dz/dV–V) curves and dI/dV mapping measurements reveal that the resonant tunneling between the image potential states (IPSs) on Cu(001) and the Fermi level of the STM tip leads to drastic variations of these features.     

Carrier injection at silicide/silicon interfaces in nanowire based-nanocontacts

In this article, we investigate the silicide/Si nanowire (Si NW) interface properties based on a detailed characterization of PtSi/NW nanocontacts. For that purpose, we fabricate two-terminal structures implemented on vertical Si NWs arrays defined by a top-down approach with an ultra-high density. Each termination of Si NWs is silicided and contacted to an external metal line. The temperature dependence and the non-linearity of current–voltage (I–V) characteristics are identified as a clear signature indicating that contacts dominate the overall resistance of the Si NW arrays. It is demonstrated that this trend remains valid in the limit of extremely small NW radii and that trap-induced surface depletion also reduces the contact injection cross-section. In this context, the electrostatic landscape at the vicinity of the silicide-to-semiconductor contact interface is dominated by the field effect imposed by peripheral surface states and not by the Schottky barrier height.     

Zinc oxide based varistors: A possible mechanism

We propose a theoretical explanation of the highly nonlinear current-voltage (I–V) characteristics of ZnO based varistor ceramics, with maximum values of $\text{α =}\text{dlogI}\text{dlogV}$ of over 70 at T = 300 K. Starting with symmetrical Schottky barriers at the junctions between ZnO grains, we show that the presence of deep interface states with a very slow recombination can lead to a control mechanism for the V-dependence of the barrier height that is essential for the occurence of very high α values. The model accounts for the observed voltage and temperature dependence of α and I, and for the capacitance of ZnO varistors.     

Electrical conduction mechanism of polyvinylidenefluoride (PVDF) – polysulfone (PSF) blend film

The electrical conductivity of polyvinylidenefluoride (PVDF) – polysulfone (PSF) blend films have been measured by studying the I–V characteristics in the temperature range of 298–398 K. The results are shown by measuring the dependence of current on field, temperature, and blending compositions in the form of I–V characteristics and analysis has been made by interpretation of Poole–Frenkel, Schottky ln (J) vs. T plots, Richardson and Arrhenius plots. For individual polymers, the conduction mechanism observed to be a Poole–Frenkel type. On blending, the charge conduction appears to be the Schottky emission at lower temperature while Poole–Frenkel mechanism at higher temperature. The analysis of these results suggests that Pool–Frenkel mechanism is mainly responsible for the observed conduction. The conductivity was found to increase with an increase in the polysulfone concentration in the blend; it could be justified in terms of mobility of charge carriers. It is found that mobility of charge carriers increases with the increase in polysulfone concentration in the blend.     

Synthesis and characterisation of glycine sodium nitrite crystals having non linear optical behaviour

Glycine sodium nitrite (GSNi) having non linear optical efficiency more than KDP crystal has been obtained from solutions by slow cooling technique. The crystals are found to be chemically and thermally stable with orthorhombic unit cell. The presence of wide transparency window in UV–Visible region makes GSNi suitable for opto-electronic device applications. It has second harmonic generation efficiency of 1.273 times that of standard KDP crystal. GSNi crystal belongs to soft category of materials with work hardening index of 2.33. Crystals introduced in timer circuit gave a stable output with the capacitance value of 236 pF. I–V characteristic indicates a safe operating range of 300 V/cm. GSNi is seen to behave as a normal dielectric with applied frequency and crystals exposed to light exhibit negative LDR characteristic which is attributable to space charge formation.     

Dynamics of order parameter fluctuations in gapless superconductors below Tc

The dynamical pairfield susceptibility of gapless superconductors has been calculated using the theory of Gorkov and Eliashberg and improvements thereof. The result differs drastically from the usual Ginzburg-Landau theory and agrees qualitatively with recent experiments on the I–V characteristic of tunnel junctions with Al films.     

Electrical conduction in coevaporated antimony trisulphide films

Antimony trisulphide films were prepared by the three temperature method. The temperature dependence of conductivity for films prepared at different substrate temperatures were measured. The I–V characteristics of the Sb-Sb₂S₃-Sb systems studied showed a space charge limited conduction indicating a I ∝ V² /d³ dependence. The trap density and the trap energy level were determined.     

Phase diagram of Bi up to 140 kbars

The phase diagram of Bi has been studied by resistometric techniques in the temperature range of 30 to 300°K up to pressures of 140 kbars. Using the original Bridgman phase notation, the phase transitions I–II, II–III, I–III, III–IV and V–VI were observed. Two new phases, designated VIII and IX were observed in this region. The triple points occurring between I–II–III near 29.5 kbars and 160°K, between IV–V–VIII near 55 kbars and 240°K, between V–VI–VIII near 72 kbars and 255°K and between VI–VIII–IX near 135 kbars and 250°K. Earlier measurements were adjusted to the 1970 Drickamer pressure scale and compared to the present results. A phase diagram is proposed for pressures to 140 kbars. Calculations of the volume changes and latent heats of transformation are made near the triple points I–II–III, IV–V–VIII and V–VI–VIII using the measured volume changes of Bridgman for the I–II, IV–V and V–VI transitions. The latent heat associated with the III–IV transition was calculated using the volume data of Bridgman to be less than ? 2 cal/mol.