Occurrence Of Negative Differential Resistance Research Articles

Exploring the Odd–Even Effect, Current Stabilization, and Negative Differential Resistance in Carbon-Chain-Based Molecular Devices

The transport properties of molecular devices based on carbon chains are systematically investigated using a combination of non-equilibrium Green’s function (NEGF) and density functional theory (DFT) first-principle methods. In single-carbon-chain molecular devices, a distinct even–odd behavior of the current emerges, primarily influenced by the density of states (DOS) within the chain channel. Additionally, linear, monotonic currents exhibit Ohmic contact characteristics. In ladder-shaped carbon-chain molecular devices, a notable current stabilization behavior is observed, suggesting their potential utility as current stabilizers within circuits. We provide a comprehensive analysis of the transport properties of molecular devices featuring ladder-shaped carbon chains connecting benzene-ring molecules. The occurrence of negative differential resistance (NDR) in the low-bias voltage region is noted, with the possibility of manipulation by adjusting the position of the benzene-ring molecule. These findings offer a novel perspective on the potential applications of atom chains.

Negative differential resistance in armchair silicene nanoribbons

Due to dimensional confinement of carriers and non-trivial changes in the electronic structure, novel tunable transport properties manifest in nanoscale materials. Here, we report using first-principles density functional theory and non-equilibrium Green’s function formalism, the occurrence of negative differential resistance (NDR) in armchair silicene nanoribbons (ASNRs). Interestingly, NDR manifests only in pristine ASNRs, where . We show that the origin of such a novel transport phenomenon lies in the bias-induced changes in the density of states of this particular family of nanoribbons. With increasing width of the nanoribbons belonging to this family, the peak-to-valley ratios of current decrease due to the increase in the number of sub-bands leading to a reduction in NDR. NDR is possible not only in ASNRs, but also in mixed configurations of armchair and zigzag silicene nanoribbons. This universality of NDR along with its unprecedented width-induced tunability can be useful for silicene-based low-power logic and memory applications.

Electrical properties of ultrafine nylon-6 nanofibers prepared via electrospinning

We report on the preparation and electrical characterization of nylon-6 nanofibers via electrospinning technique. During electrospinning, the polymer solution became highly ionized and emerging out of the micro-tip syringe by forming mesh-like ultrafine nanofibers structure in between the main fibers. The resultant nylon-6 nanofibers were well-oriented with uniform structure. The diameter of the ultrafine nanofibers (7 to 40 nm) is one order less than those of main fibers (100 to 200 nm). The current-voltage (I-V) measurements revealed a linear curve with an occurrence of negative differential resistance (NDR) behavior. The existence of NDR region in the nylon-6 nanofibers can be attributed to the tunneling current through the ultrafine structures. The fabrication of nanofibers, in the form of ultrafine mesh-like form, is relatively fast and inexpensive, and it paves the way to build up of new dimension for nano device applications.

Quantized space-charge waves in quasi-2D

Hot-electron transport theory of standard semiconductor layered structures predicts the occurrence of negative differential resistance (NDR) associated with inter-valley electron transfer, negative effective mass, and real-space transfer. An analysis of the growth of quantized space-charge waves in single and double heterostructures in which no real-space transfer occurs is presented. It is shown that, in contrast to the situation in bulk material, growth is a complicated function of wave-vector because of quantization effects. As a consequence, growth is limited by quantization effects and diffusion to small wave-vectors. To illustrate the effect of quantization clearly, the analysis is limited to growth within the lowest sub-band. In spite of quantization differences, a quantitative comparison can be made by a simple rescaling. Growth is shown to be severely limited to small wave-vectors and its rate turns out to be independent of the details of quantization, being that for extreme confinement. The rate maximizes for a wave-vector of about 4 × 105 cm−1 corresponding to a frequency of 700 GHz. The criterion for domain formation in GaN systems becomes n02L≥1020cm-3, where n0 is the areal density of electrons and L is the sample length. As far as growth rate is concerned, the restriction to the lowest sub-band represents a worst-case scenario.

Significant negative differential resistance predicted in scanning tunneling spectroscopy for aC60monolayer on a metal surface

We theoretically predict the occurrence of negative differential resistance (NDR) in scanning tunneling spectroscopy for a pure ${\text{C}}_{60}$ monolayer deposited on a metal surface using metal tips, namely, on a Cu(111) surface and using various W tips. It is proposed that the likely reason why NDR has not been observed under such conditions is that NDR can be reduced if an oxidized or Cu-terminated tip is used. A detailed decomposition of the total tunneling current into its contributions from individual molecular orbitals reveals that only some of the orbitals on the tip and on the ${\text{C}}_{60}$ can be ``matched up'' to give a contribution to the current and that the NDR is a consequence of the mismatch between these specific orbitals within particular ranges of bias voltage. Moreover, the NDR characteristics, including the peak positions and the peak-to-valley ratios, are found to depend on the tip material, tip geometry, and tip-to-molecule position.

Coulomb staircase with negative differential resistance at room temperature for a metal tip-metal dot-semiconductor double junction

Nanometer-sized Au dots have been fabricated on p-type Si(111) substrates by field-induced transfer of tip material in a scanning tunneling microscope (STM). Positioning the STM tip on a very small dot (10–15 nm in diameter) allows observation of equidistant steps with a spacing of several 100 mV and regions with negative differential resistance (NDR) in the current-voltage characteristic. Numerical simulations confirm that the capacitance between the tip and the Au dot falls into the 10 −19 F range. The occurrence of NDR might be explained by a leaking of excess carriers from the dot to the immediate surroundings.

Heterostructure confinement effect on the negative-differential-resistance (NDR) bipolar transistor

We review the current investigation of heterostructure-emitter bipolar transistors (HEBT) and pay attention to confinement effects on the common-emitter current gain and the occurrence of negative-differential resistance (NDR). Three main devices with different heterostructure emitters have been grown and discussed. These devices include single-(SHEBT), double-(DHEBT), and resonant tunneling-(RT-HEBT) structure with Al0.5Ga0.5As/500Å-GaAs, Al0.5Ga0.5As/500Å-GaAs and 5-period 50Å-Al0.5Ga0.5As/50Å-GaAs superlattic emitters, respectively. With respect to current gain, it is found that Al0.5Ga0.5As/500Å-GaAs gives the best confinement effect on hole minority carriers We obtain common-emitter current gains of 180, 18, and 65 for the SHEBT, DHEBT and RT-HEBT, respectively. Besides, all of the studied devices exhibit an interesting S-shaped negative-differential resistance (NDR) resulting from the regenerative switching process. With respect to NDR performance, the Al0.5Ga0.5As/500Å-GaAs, shows the best confinement effect on the ionized electrons. The controlled voltage efficiencies are 1.43, 1.77, and 1.12 for SHEBT, DHEBT, and RT-HEBT, respectively.

Thomas–Fermi approach to resonant tunneling in δ-doped diodes

We study resonant tunneling in B-δ-doped diodes grown by Si-molecular beam epitaxy. A Thomas–Fermi approach is used to obtain the conduction-band modulation. Using a scalar Hamiltonian within the effective-mass approximation we demonstrate that the occurrence of negative differential resistance (NDR) only involves conduction-band states, whereas interband tunneling effects seem to be negligible. Our theoretical results are in very good agreement with recent experimental observations of NDR in this type of diode.