Resonant Tunneling Behavior Research Articles

PHOTON-ASSISTED TRANSPORT CHARACTERISTICS THROUGH QUANTUM DOT COUPLED TO SUPERCONDUCTING RESERVOIRS

The influence of time-varying fields on the transport through a mesoscopic device has been investigated. This mesoscopic device is modeled as a quantum dot coupled to superconducting reservoirs via quantum point contact. The effect of a magnetic field and the Andreev reflection process were taken into account. The conductance was deduced by using Landuaer–Buttiker equation. A numerical calculation has been performed that shows a resonant tunneling behavior. Such investigation is important for fabricating photoelectron mesoscopic devices.

Monolayers and nanoparticles on nickel silicide for molecular electronics

We describe the use of nickel silicide as an electrode in molecular electronics applications. Formation of monolayers of aliphatic and aromatic hydrocarbons on nickel silicide is demonstrated, and these monolayers are used to link CdSe nanocrystals to the substrate. Using the conjugated linker molecule 1,4-ethynylphenyl-2′-nitro-1-benzene-dithiolate, scanning tunneling spectroscopy measurements at 120K show evidence of Coulomb blockade and resonant tunneling behavior associated with the nanocrystals. These measurements demonstrate the feasibility of using nickel silicide as an electrode in molecular electronic devices.

Resonant tunneling in a quantum step: Inverse photoemission spectroscopy ofAg∕Al(100)

Inverse photoemission spectroscopy has been used to study the electronic structure of thin Ag layers adsorbed on Al(100). The experimental thickness dependence of the emitted photon intensities is described in terms of quantum size effects in a one-dimensional system. The quantum confinement displayed by our data originates in the reflection from a barrier-less electronic potential, at the $\mathrm{Ag}∕\mathrm{Al}$ interface. One of the electronic features displays a resonant tunneling behavior associated with transmission through an energy gap of the metallic thin film.

Discrete easy-axis tilting inMn12-acetate, as determined by EPR: Implications for the magnetic quantum tunneling mechanism

The variation with microwave frequency and temperature of previously reported anomalous peaks in the EPR spectra of ${\mathrm{Mn}}_{12}$-acetate, under large transverse fields, reveals that the molecular easy magnetization axes are tilted with respect to the global symmetry direction. More importantly, on the basis of the angle dependence of fine structures observed in the EPR spectra we infer that the tilt distribution must be discrete, as was previously suspected from studies which demonstrated the presence of a locally varying rhombic anisotropy [S. Hill et al., Phys. Rev. Lett. 90, 217204 (2003)]. The tilts are confined to two orthogonal planes, and the distribution extends up to $\ensuremath{\sim}1.7\ifmmode^\circ\else\textdegree\fi{}$ degrees away from the global easy $(z)$ axis. We ascribe the tilting to the hydrogen-bonding effect associated with the disordered acetic acid solvent molecules. The effect is considerably larger than deduced from x-ray diffraction analyses. These data constitute the sought-after evidence for the presence of transverse fields in ${\mathrm{Mn}}_{12}$-acetate, and provide a possible explanation for the lack of selection rules in the resonant quantum tunneling behavior seen in low-temperature hysteresis experiments for this $S=10$ system.

Resonant tunneling behavior and discrete dopant effects in narrow ultrashort ballistic silicon-on-insulator metal-oxide-semiconductor field-effect transistors

We utilize an efficient, fully quantum mechanical approach to calculating ballistic transport in a fully depleted, silicon-on-insulator metal-oxide-semiconductor field-effect transistor in three dimensions to examine realistic devices with quantum wire channels. We find that, by including the atomistic nature of these small devices in the simulation, we observe variations in the threshold voltage dependent on the position of the dopants in the channel. Further, we find that the narrow channel access geometry creates a situation in which the impinging electron density in the source undergoes resonant tunneling in order to reach the drain end of the device.

Environment and structure influence on DNA conduction

Results for transmission through the poly(G) DNA molecule are presented. We show that (i) periodically arranged sodium counter-ions in close proximity to dry DNA gives rise to a new conduction channel and aperiodicity in the counter-ion sequence can lead to a significant reduction in conduction, (ii) modification of the rise of B-DNA induces a change in the width of the transmission window, and (iii) specifically designed sequences are predicted to show intrinsic resonant tunneling behavior.

Nanowire resonant tunneling diodes

Semiconductor heterostructures and their implementation into electronic and photonic devices have had tremendous impact on science and technology. In the development of quantum nanoelectronics, one-dimensional (1D) heterostructure devices are receiving a lot of interest. We report here functional 1D resonant tunneling diodes obtained via bottom-up assembly of designed segments of different semiconductor materials in III/V nanowires. The emitter, collector, and the central quantum dot are made from InAs and the barrier material from InP. Ideal resonant tunneling behavior, with peak-to-valley ratios of up to 50:1 and current densities of 1 nA/μm2 was observed at low temperatures.

Many-body approach to spin-dependent transport in quantum dot systems.

By means of a diagram technique for Hubbard operators, we show the existence of a spin-dependent renormalization of the localized levels in an interacting region, e.g., quantum dot, modeled by the Anderson Hamiltonian with two conduction bands. It is shown that the renormalization of the levels with a given spin direction is due to kinematic interactions with the conduction subbands of the opposite spin. The consequence of this dressing of the localized levels is a drastically decreased tunneling current for ferromagnetically ordered leads compared to that of paramagnetically ordered leads. Furthermore, the studied system shows a spin-dependent resonant tunneling behavior for ferromagnetically ordered leads.

Resonant versus Anti-Resonant Tunneling at Carbon Nanotube A-B-A Heterostructures

Narrow antiresonances going to zero transmission are found to occur for general (2n,0)(n,n)(2n,0) carbon nanotube heterostructures, whereas the complementary configuration, (n,n)(2n,0)(n,n), displays simple resonant tunneling behaviour. We compute examples for different cases, and give a simple explanation for the appearance of antiresonances in one case but not in the other. Conditions and ranges for the occurence of these different behaviors are stated. The phenomenon of anti-resonant tunneling, which has passed unnoticed in previous studies of nanotube heterostructures, adds up to the rich set of behaviors available to nanotube based quantum effect devices.

Resonant Tunnelling Behaviour in Multilayered Cold Cathodes Made of Nanoseeded Diamond and Nanocluster Carbon

ABSTRACTMultilayered cold cathodes made of spin coated nanocrystalline diamond and cathodic arc process grown nanocluster carbon films, were studied. The nanocrystalline diamond was first coated on to the substrate. The nanocluster carbon films were then deposited on the seeded nanocrystalline diamond coated substrates using the cathodic arc process at room temperature. Theresultant hetrostructured microcathodes were observed to exhibit electron emission currents of 1μA/cm2 at fields as low as 1.2 V/μm. Further some of the samples seem to exhibit I-V characteristics witha negative differential resistance region at room temperature conditions. This negative differential resistance or the resonant tunneling behaviour was observed to be dependent on the nanoseeded diamond size and concentration for a given nanocluster carbon film.

Ferromagnet–semiconductor device with tunable tunnel characteristics

A device is proposed consisting of a GaAs/AlxGa1−xAs heterostructure with a ferromagnetic strip placed on top that has an easy axis of magnetization perpendicular to the underlying two-dimensional electron gas. In addition, the strip is gated to form a combined magnetostatic and electrostatic barrier for the conduction electrons. On the basis of a simple model, which is of the Landauer–Büttiker type, such a structure is shown to have three different regimes of operation. Whereas for a certain regime, electrons can move according to the classical diamagnetic motion, there is also the possibility of tuning the device between nonresonant and resonant tunneling behavior. In the latter case the combined magnetostatic and electrostatic barrier acts as an energy and momentum filter. The proposed device could find application in digital logic circuits as an electromagnetic field-effect transistor.

Field emission from heterostructured nanoseeded diamond and nanocluster carbon cathodes

ABSTRACTNovel heterostructured cold cathodes made of nanoseeded diamond and cathodic arc process grown nanocluster carbon films, were studied. The nanocrystalline diamond with varying diamond concentration was first coated on to the substrate. The nanocluster carbon films were then deposited on the nanoseeded diamond coated substrates using the cathodic arc process at room temperature. The resultant heterostructured microcathodes were observed to exhibit electron emission currents of 1μA/cm2 at low fields of 1.2 - 5 V/μm. Further some of the samples seem to exhibit I-V characteristics with a negative differential resistance region at room temperature conditions. This negative differential resistance or the resonant tunneling behaviour was observed to be dependent on the nanoseeded diamond concentration.

Photoluminescence Study of Resonant Tunneling Transistor with p+/n-Junction Gate

We studied photoluminescence (PL) of a resonant tunneling transistor with a p+/n-junction gate. The excitation energy was selected to be close to the band-gap energy of the GaAs collector layer 1) so as not to excite the barrier layer and quantum well directly, and 2) in order to obtain a simple luminescence spectrum. The PL signal shows strong correlation with the resonant tunneling current. The PL peak position shows a redshift with increasing collector voltage, indicating the existence of the quantum-confined Stark effect. The collector voltage dependence of the PL linewidth suggests the existence of charge accumulation in the quantum well. The accumulated electron density and the charging time were estimated. It was also shown that the PL intensity could be controlled by the gate voltage without affecting the resonant tunneling behavior of electrons.

Non-commutative polynomials and the transport properties in multichannel-multilayer systems

Using the transfer-matrix technique to describe transport properties in multichannel-multilayer systems, a three-term non-commutative matrix recurrence relation is deduced and solved. The matrix polynomials obtained in this way allow one to write compact expressions for the n-cell transmission amplitudes, from channel to channel i. In the one-dimensional, one-channel limit, the non-commutative polynomials reduce to the well known Chebyshev orthogonal polynomials. To illustrate the role of these polynomials in the resonant tunnelling and channel-mixing behaviour, we discuss one- and two-channel examples.

The transient transmission through a quantum dot under the influence of oscillating external fields

We consider a quantum dot coupled to two leads in the presence of oscillating external fields applied to the dot and the two leads. Using the nonequilibrium-Green-function method, the formula for the transient transmission probability (TTP) is derived. The numerical studies reveal the following facts. When ( is the full width of the resonant state), no visible resonant tunnelling behaviour occurs, and strongly depends on the time at which the electron enters the dot, t, and that at which it exits from it, ; when , the resonant tunnelling becomes striking, and depends only weakly on t and . The conventional transmission probability , defined as the limit as and , has a very rich spectrum and exhibits a simultaneous quenching of some channels. On the basis of the properties of , the condition for the occurrence of an electron-photon pump has also been discussed.

Molecular Wire Interconnects: Chemical Structural Control, Resonant Tunneling and Length Dependence

Molecular wires have several promising features, that would appear to make them ideal for advanced interconnects in nanoscale electronic devices. We discuss several aspects of the linear and nonlinear conductance of molecular wire interconnects. Topics include energy dependence of molecular conductance, resonant tunneling behavior, control of conductance by molecular structure and geometry, length dependence including the tunneling regime energetics. Design rules using molecular interconnects will differ substantially from those with more standard, lithographically structured silicon interconnects. In particular, the dissipation mechanisms will differ, both tunneling and ballistic regimes should be available, coulomb blockade and staircase behavior will be observed (but under differing conditions) and fabrication of gate electrodes is a challenge.

Transmission coefficients for resonant tunneling in multi-barrier graded quantum well semiconductor heterostructures

Resonant tunneling of electrons is studied in a new class of multi-barrier semiconductor heterostructures which contain graded quantum wells, whose slopes can be changed by varying the alloy composition of the constituent material. Such systems, in the presence of an externally applied bias, can exhibit resonant tunneling behavior that is quite different from previously studied multi-barrier materials, because of the unique coupling of the quasi-bound states between the graded quantum wells. In this paper, we explicitly compute the electron transmission coefficient T( E) for such systems as a function of the multi-barrier geometry and internal slopes of the quantum wells to obtain novel transmission coefficient spectra and discuss their implications.

Resonant tunneling and low-energy impurity behavior in a resonant-level model.

We study the effect of screening of an impurity charge by conduction electrons on resonant tunneling at arbitrary energy of the impurity level. We examine the exactly solvable model of the resonant level. We find the ground-state solutions of the model at all possible Coulomb interactions. The principle of equivalence between its universal behavior and the Kondo model is proved. However, the dependence of its scale invariant variable on the bare variables has different forms in two different regions of the parameter variations. This means that besides the well-known Kondo-like fixed point of the renormalization at weak Coulomb interaction a new stable point exists. The latter determines a singular low-energy behavior of the impurity

Tunneling dynamics in CdTe/(Cd,Zn)Te asymmetric double-quantum-well structures.

Carrier tunneling through (Cd,Zn)Te barriers of different thicknesses is investigated in CdTe/Cd,Zn)Te asymmetric double quantum wells by use of time-resolved photoluminescence and steady-state photoluminescence excitation experiments. The strong dependence of the observed tunneling times on the barrier thickness indicates a resonant tunneling behavior. The analysis of our results allows us to identify the importance of excitons rather than free-carrier states for the tunneling mechanism.

Metallic quantum wells grown by molecular-beam epitaxy

Ultrathin single crystal buried metal layers of NiAl have been grown within (Al,Ga)As heterostructures. The layers are electrically continuous down to 1 nm in thickness. Furthermore, property changes such as increased in-plane electron–electron interactions, and vertical transport resonant tunneling behavior, attributed to the decreased dimensionality of such ultrathin layers, demonstrate that, in this regime, the films can be considered as metallic quantum wells. The resonant tunneling has been exploited in making a three-terminal buried metallic well device. We discuss initial results of promising experiments aimed at decreasing the lattice mismatch between the metal and the semiconductor (1) by adding In to the GaAs and (2) by substituting the more closely lattice-matched CoAl for NiAl.