Bias Current Characteristics Research Articles

Stability of destructive quantum interference antiresonances in electron transport through graphene nanostructures

We investigate the stability of destructive quantum interference (DQI) in electron transport through graphene nanostructures connected to source and drain electrodes. The fingerprint of DQI is an antiresonance in the transmission function, and its origin is deeply connected to the topology of the atomic structure, which we discuss in terms of symmetry arguments supported by numerical simulations. A systematic analysis of the transmission function versus system size reveals that the DQI antiresonance persists for large systems in the ballistic regime and establishes the quantum confinement gap as the intrinsic resolution limit to detect QI effects. Furthermore, we consider the influence of disorder, electron–electron and electron–phonon interactions, and provide quantitative criteria for the robustness of DQI in their presence. We find that the conductance is quite sensitive to perturbations, and its value alone may not be sufficient to characterize the quantum interference properties of a junction. Instead, the characteristic behavior of the transmission function is more resilient, and we suggest it retains information on the presence of an antiresonance even if DQI is partially concealed or suppressed. At the same time, DQI results in a non-linear transport regime in the current-bias characteristics that can be possibly detected in transport experiments.

Asymmetry and nonlinearity of current-bias characteristics in superfluid–normal-state junctions of weakly interacting Bose gases

We uncover current-bias characteristics of superfluid-normal state junctions with weakly-interacting Bose gases. It is shown that in the presence of a chemical potential bias the characteristics can strongly be asymmetric for origin. The salient feature that is absent in the fermionic counterpart arises from a tunneling process associated with a condensate and a bosonic Andreev reflection process. It turns out that such processes are intrinsically nonlinear and therefore do not obey Ohm's law even at a low bias. In addition, the remaining processes are found to obey Ohm's law and become dominant for transport driven by a temperature bias.

Charge transport in graphene-based mesoscopic realizations of Sachdev-Ye-Kitaev models

We consider a recent proposal for a physical realization of the Sachdev-Ye-Kitaev (SYK) model in the zeroth-Landau-level sector of an irregularly-shaped graphene flake. We study in detail charge transport signatures of the unique non-Fermi liquid state of such a quantum dot coupled to non-interacting leads. The properties of this setup depend essentially on the ratio $p$ between the number of transverse modes in the lead $M$ and the number of the fermion degrees of freedom $N$ on the SYK dot. This ratio can be tuned via the magnetic field applied to the dot. Our proposed setup gives access to the non-trivial conformal-invariant regime associated with the SYK model as well as a more conventional Fermi-liquid regime via tuning the field. The dimensionless linear response conductance acquires distinct $\sqrt{p}$ and $1/\sqrt{p}$ dependencies for the two phases respectively in the low-temperature limit, with a universal jump at the transition. We find that corrections scale linearly and quadratically in either temperature or frequency on the two sides of the transition. In the weak tunneling regime we find differential conductance proportional to the inverse square root of the applied voltage bias $U$. This dependence is replaced by a conventional Ohmic behavior with constant conductance proportional to $1/\sqrt{T}$ for bias energy $eU$ smaller than temperature scale $k_BT$. We also describe the out-of-equilibrium current-bias characteristics and discuss various crossovers between the limiting behaviors mentioned above.

The Effects of Thermal Neutron Irradiation on Current-Voltage and Capacitance-Voltage Characteristics of Au/n-Si/Ag Schottky Barrier Diodes

To observe the neutron transmutation and displacement damage effects, Au/n-Si/Ag Schottky barrier diodes were exposed to thermal neutron irradiation. Irradiation induced changes in Schottky barrier height, saturation current, and donor concentration were investigated by using current-voltage (I-V) and capacitance-voltage (C-V) characteristics of the diodes. The irradiation for 10 s caused a little change in the Schottky diode parameters which were obtained from I-V and C-V measurements. Observable changes in the parameters occurred after the second irradiation of 30 s duration. After the total dose, an increase in saturation current and barrier height inhomogeneties took into place and a decrease in carrier concentration was observed due to the carrier removal effect of thermal neutron-induced damages. Whereas the values of zero bias barrier height have little change after irradiations, the values of ideality factor increased after irradiations. The values of zero-bias barrier height for all diodes was also calculated from reverse bias current characteristics. After second dose, the values of zero-bias barrier height decreased for all diodes. The values of series resistance were determined by Cheung functions before and after irradiations. Before irradiations, the values were found between 2.10 kΩ and 2.76 kΩ. After second dose, the values of series resistance of all diodes decreased and were found between 1.59 kΩ and 2.20 kΩ. Furthermore, the proof of thermal neutron transmutation of elements in the devices was given via energy dispersive spectroscopy (EDS) mapping.

A comparative electrical transport study on Cu/n-type InP Schottky diode measured at 300 and 100 K

Two oxygen plasma treated InP samples with different plasma powers of 100 and 250 W were prepared and a comparative study on the electrical properties of Cu/n-type InP Schottky diode measured at 300 and 100 K was performed to investigate the current transport mechanism in detail. The forward and reverse bias current–voltage (I–V) characteristics were analyzed with considering various transport models. The fitting to the forward bias I–V characteristics revealed that relatively high ideality factor at 300 K for untreated sample were related with the generation-recombination (GR) current and the large E00 value at 100 K for 100 W plasma treated sample were associated with more significant tunneling effect. The analyses on the reverse bias current characteristics showed the suitable current transport model has changed from thermionic emission (TE) to TE combined with barrier lowering for both untreated and 250 W treated samples and from TE + BL to thermionic field emission for 100 W treated sample with increasing temperature from 100 to 300 K.

Electronic and transport properties of T-graphene nanoribbon: Symmetry-dependent multiple Dirac points, negative differential resistance and linear current-bias characteristics

Based on the tight-binding method and density functional theory, band structures and transport properties of T-graphene nanoribbons are investigated. By constructing and solving the tight-binding Hamiltonian, we derived the analytic expressions of the linear dispersion relation and Fermi velocity of Dirac-like fermions for armchair T-graphene nanoribbons. Multiple Dirac points, which are triggered by the mirror symmetry of armchair T-graphene nanoribbons, are observed. The number and positions of multiple Dirac points can be well explained by our analytic expressions. Tight-binding results are confirmed by the results from density functional calculations. Moreover, armchair T-graphene nanoribbons exhibit negative differential resistance, whereas zigzag T-graphene nanoribbons have linear current-bias voltage characteristics near the Fermi level.

PREDICTING THE PATH OF ELECTRONIC TRANSPORT THROUGH A MOLECULAR DEVICE VIA A MOUNTAIN-PASS ALGORITHM

The so-called “mountain-pass” theorem allows for the finding of a critical point on the path between two points on a multidimensional contour where the maximal elevation is minimal. By implementing the “elastic string algorithm”, it is possible to not only find the critical point, but to compute the mountain-pass itself on a finite-dimensional contour. For a given molecule that sits between two probes making up a nanostructure device, we propose that the mountain-pass will be a likely path of electron transport through the molecule, the contour being the electronic potential of the molecule. This potential along this path will be used as the input potential for SETraNS, a 1D Wigner-Poisson electron transport solver in order to explore the current-bias characteristics of such the molecule in such a device. In order to calculate the mountain pass, the elastic string algorithm is used to set up a constrained non-linear optimization problem which is, in turn, solved via a Monte Carlo method. We will compute the mountain-pass for a well-known test contour in order to show the validity of this approach. The procedure developed here is to be combined with conformational analysis via the molecular modeling program AMBER and the quantum transport program SETraNS in order to predict molecular function. When achieved, this combined procedure will allow for the better design and implementation of nanoscale molecular devices for application such as sensing, switching and data processing.

The role of the interface insulator layer and interface states on the current-transport mechanism of Schottky diodes in wide temperature range

In order to interpret in detail the experimentally observed current–voltage–temperature ( I– V– T) and capacitance–voltage–temperature ( C– V– T) results of Al/p-Si metal–semiconductor Schottky barrier diodes (SBDs) we have been examined the samples in the temperature range of 150–375 K. In the calculation method, to confirm the relationship between the I– V– T and C– V– T results, we have reported a modification which includes the ideality factor, n, and tunnelling parameter δχ 1/2 in the forward bias current characteristics. In the intermediate bias voltage region (0.1 < V < 0.6 V), the semi-logarithmic plots of the forward I– V– T curves were found to be linear. From the reverse saturation currents I 0 obtained by extrapolating the linear region of curves to zero applied voltage, the values of zero bias barrier heights ϕ B0 were calculated at each temperature. The values of ideality factor calculated from the slope of each curves were plotted as a function of temperature. The values of n are 3.41–1.40 indicating that the Al/p-Si diode does obey the thermionic field emission (TFE) mechanism rather than the other transport mechanism, particularly at low temperature. The high value of ideality factors is attributed to high density of interface states in the SBDs. The temperature dependence energy density distribution profile of interface state was obtained from the forward bias I– V– T measurements by taking into account the bias dependence of the effective barrier height and ideality factor. The interface states density N ss decreasing with increasing temperature was interpreted by the result of atomic restructuring and reordering at the metal–semiconductor interface. After the modification was made to the forward current expression, we obtained a good agreement between the values of barrier height obtained from both methods over a wide temperature.

Study of the breakdown voltage in lateral polysilicon N +P junctions

Lateral N +P junctions are realised on polycrystalline silicon layers. The polysilicon films are deposited by the low pressure chemical vapour deposition (LPCVD) method on silicon oxide. The reverse current-bias characteristics and the breakdown voltage are plotted and analysed for different temperatures. It is shown that at low temperature, the current is due to tunnelling. This can be explained by the ionisation of traps localised in grains boundaries. At high temperature, electrical conduction is controlled by thermal emission. It is also shown that the breakdown voltage decreases when the temperature increases.

Designing nanometre silicon-on-insulator MOSFET with buried Si 1− xGe x quantum well channel

We study the device characterization of Si-on-insulator (SOI) metal-oxide-semiconductor field effect transistor (MOSFET) with buried Si 1− x Ge x quantum well (QW) channel. Accurate quantum mechanical description of the p-channel of the buried Si 1− x Ge x QW shows that the peak carrier concentration in the conduction channel is higher in the positively graded SiGe QW, whereas the carriers are more uniformly distributed in the retrograded QW. By phenomenologically introducing a physical parameter to describe the energy relaxation of transmitting wave due to various scattering processes, systematic simulation about quantum wave transmissions of our SOI MOSFET indicates normal current-bias characteristics at nanometre regime. A threshold gate bias of about 0.6 V is obtained for both the positively graded and retrograded SiGe QWs.

Space-charge-limited-current diode model for the rectifying-to-ohmic transition with Au/Al contacts to CdS

The space-charge-limited-current diode model indicates that the rectifying-to-ohmic transition properties of Au/Al contacts to CdS are controlled by a trap at 0.6 eV below the conduction-band edge of the CdS interface with the metal. The trap densities vary between 4 and 10 (1016) cm−3 and the rectification degrades as the band bending asymmetry in the interface decreases from 0.206 to 0.158 eV with the introduction of the Al. The model provides a good fit of both the forward bias current and the nonsaturating reverse bias current characteristics using parameter values that are consistent with those found by other workers using deep-level transient spectroscopy.