Resonant Tunneling Effect Research Articles

Investigation of Time-Dependent UV-Ozone Treatment on an Ultra-Thin AgF Buffer Layer for Organic Light-Emitting Diodes

The effect of ultraviolet (UV)-ozone treatment on an ultrathin AgF buffer layer deposited on indium tin oxide (ITO) substrate was studied for various layer thicknesses and treatment times. Work function was estimated from X-ray photoelectron spectroscopy, and surface properties were calculated from measured contact angles using H2O and CH2I2 as test liquids. With improper UV-ozone treating times, no luminance was induced by current at a low voltage due to the resonant tunneling effect or a damaged film surface. However, the surface energy, surface polarity and work function were increased by proper treatment of the ultra-thin AgF film, and the resonant tunneling effect was simultaneously eliminated, resulting in improvement in device performance. An optimal thickness AgF (2 nm) with proper UV-ozone treatment time (1 min) significantly improved device performance (ITO/AgF/NPB/Alq3/LiF/Al). Our results indicate that the device efficiency of OLEDs can be greatly enhanced by simultaneous control of AgF film thickness and UV-ozone exposure time.

Resonant tunneling in superfluid3He

The $A$ phase and the $B$ phase of superfluid He-3 are well studied, both theoretically and experimentally. The decay time scale of the $A$ phase to the $B$ phase of a typical supercooled superfluid $^3$He-A sample is calculated to be $10^{20,000}$ years or longer, yet the actual first-order phase transition of supercooled $A$ phase happens very rapidly (in seconds to minutes) in the laboratory. We propose that this very fast phase transition puzzle can be explained by the resonant tunneling effect in field theory, which generically happens since the degeneracies of both the $A$ and the $B$ phases are lifted by many small interaction effects. This explanation predicts the existence of peaks in the $A \to B$ transition rate for certain values of the temperature, pressure, and magnetic field. Away from these peaks, the transition simply will not happen.

Resonant tunneling structures based on epitaxial graphene on SiC

Recently some experiments have suggested that graphene epitaxially grown on SiC can exhibit an energy bandgap of 260 meV, which enhances the potential of this material for electronic applications. On this basis, we propose to use spatial doping to generate graphene-on-SiC double-barrier structures. The non-equilibrium Green's function technique for solving the massive Dirac model is applied to highlight typical transport phenomena such as the electron confinement and the resonant tunneling effects. The I–V characteristics of graphene resonant tunneling diodes were then investigated and the effect of different device parameters was discussed. It is finally shown that this kind of double-barrier junction provides an efficient way to confine the charge carriers in graphene and to design graphene resonant tunneling structures.

Computational study of dopant segregated nanoscale Schottky barrier MOSFETs for steep slope, low SD-resistance and high on-current gate-modulated resonant tunneling FETs

We study here, using non-equilibrium Green’s function quantum simulations, the impact of dopant segregation (DS) on Schottky barrier (SB) nanoscale transistors for the implementation of ultimate CMOS with low series resistance and steep slope. Owing to their adequate multi-barrier structure, DS–SB transistor can present a gate modulated barrier resonant tunneling (MBRT) effect that allows them to have improved ION/IOFF ratio, even breach the kT/q subthreshold slope limit of classical MOSFET and therefore pave a way towards steep slope, low S/D resistance electronics. However, as shown here, these improved characteristics rely in a quite narrow window of dopant segregation parameters. Also sub-kT/q slopes are very sensitive to scattering. However, on the contrary to a standard MOSFET, electron–phonon scattering should improve on-current and ION/IOFF performances of SB-FETs and provide them with on-current levels comparable to standard MOSFETs.

Enhanced thermoelectric properties in graphene nanoribbons by resonant tunneling of electrons

Strongly enhanced thermoelectric properties are predicted for graphene nanoribbons (GNRs) with optimized pattern. By means of nonequilibrium Green's function atomistic simulation of electron and phonon transport, we analyze the thermal and electrical properties of perfect GNRs as a function of their width and their edge orientation to identify a strategy likely to degrade the thermal conductance while retaining high electronic conductance and thermopower. An effect of resonant tunneling of electrons is detected in mixed GNRs consisting of alternate zigzag and armchair sections. To fully benefit from this effect and from strongly reduced phonon thermal conductance, a structure with armchair and zigzag sections of different widths is proposed. It is shown to provide a high thermoelectric factor of merit $\mathit{ZT}$ exceeding unity at room temperature.

Electrical field and temperature effects in 2D‐2D resonant tunneling diodes based on cubic InGaN/AlGaN

AbstractThe present work reports on a study of the electron transport in a 2D‐2D resonant tunneling diode based on strained Al0.3Ga0.7N/In0.2Ga0.8N/Al0.3Ga0.7N quantum wells embedded between relaxed n‐Al0.15Ga0.85N/strained In0.2Ga0.8N emitter and collector contacts. The epilayers are assumed to be with cubic crystal structure to avoid the effects of spontaneous and piezoelectric polarization fields. The aluminum composition in both the injector and collector contacts is taken relatively weak, but large band offsets are achieved at the boundary of the preconfinement wells. The heterostructure modeled is aimed to operate at high biases and at elevated temperatures. Calculations of the band edges and quantum‐bound states were made using a self‐consistent solver of the Schrödinger and Poisson equations. Obtained results revealed: (i) a charge transfer occurs due to a resonant tunneling through a double barrier, (ii). A special attention is paid to the effects of resonant tunneling and thermal activation on the charge transfer. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Tunneling-induced coherent electron population transfer in an asymmetric quantum well

We propose an asymmetric double quantum wells structure with a common continuum and investigate the effect of resonant tunneling on the control of coherent electron population transfer between the two quantum wells. By numerically solving the motion equations of element moments, the almost complete electron population transfer from the initial subband to the target subband could be realized due to the constructive interference via flexibly adjusting the structure parameters.

Liquid refractive index sensors using resonant optical tunneling effect for ultra-high sensitivity

This paper reports the design and analysis of a liquid refractive index (RI) fiber sensor based on resonant optical tunneling effect (ROTE). The device utilizes an optical cavity formed between two angled silver-coated optical fibers to detect the RI changes by measuring the intensity variation of transmission intensity or the wavelength shift of transmission peak. The simulation results show that the intensity-based method could reach a sensitivity of 10 −7 RIU (refractive index unit) and the spectrum-based method promises a sensitivity of 81,000 nm/RIU, which are much larger than those of Fabry–Pérot etalons and surface plasmon resonance sensors. With ultrahigh sensitivity, pico-litre sample volume and fiber integration, this sensor may find potential applications in biochemical analysis.

High-resolution Measurement of Refractive Index Based on Resonant Tunneling Effect

A high-resolution measurement device of refractive index with high transmissivity and Q factor based on resonant tunneling effect is presented. The device is constructed by one dimensional photonic crystal (PC) with a defect which would produce different resonant peaks in PC band gap. These peaks are sensitive to the change of the refractive index for different mediums which are filled in the defect. It is found that with a spectrometer that can resolve a resonant peak shift of 0.5nm, at the resonant wavelength of about 1550nm, the resolution of refractive index should be better than Δn = 0.0008, and the transmissivity could be accessible to 1. Both the plane wave method and the finite difference time domain method are employed in numerical analysis. The device is suitable in a variety of applications of practical interest, since many physical, chemical, and biological parameters can be known through measurement of the refractive index.

Silica Nano-Networks as Stretches on Segmented SU8 Rods for Sub-Wavelength Photonics

The optical properties of CdBr2 were studied by first principle using the density functional theory. The dielectric functions and optical constants are calculated using the full potential-linearized augmented plane wave (FP-LAPW) method with the generalized gradient approximation (GGA). The theoretical calculated optical properties and energy Loss (EEL) spectrum yield a static refractive index of 2.1 and a plasmon energy of 13eV for hexagonal phase. The results, in comparison with the published data, are in good agreement with the experimental and previous theoretical results.

Pauli spin blockade and lifetime-enhanced transport in a Si/SiGe double quantum dot

We analyze electron transport data through a Si/SiGe double quantum dot in terms of spin blockade and lifetime-enhanced transport (LET), which is transport through excited states that is enabled by long spin relaxation times. We present a series of low-bias voltage measurements showing the sudden appearance of a strong tail of current that we argue is an unambiguous signature of LET appearing when the bias voltage becomes greater than the singlet-triplet splitting for the (2,0) electron state. We present eight independent data sets, four in the forward bias (spin-blockade) regime and four in the reverse bias (lifetime-enhanced transport) regime, and show that all eight data sets can be fit to one consistent set of parameters. We also perform a detailed analysis of the reverse bias (LET) regime, using transport rate equations that include both singlet and triplet transport channels. The model also includes the energy dependent tunneling of electrons across the quantum barriers, and resonant and inelastic tunneling effects. In this way, we obtain excellent fits to the experimental data, and we obtain quantitative estimates for the tunneling rates and transport currents throughout the reverse bias regime. We provide a physical understanding of the different blockade regimes and present detailed predictions for the conditions under which LET may be observed.

Observation of room temperature negative differential resistance in multi-layerheterostructures of quantum dots and conducting polymers

Multi-layer heterostructure negative differential resistance devices based on poly-[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylenevinylene] (MEH-PPV) conducting polymer and CdSequantum dots is reported. The conducting polymer MEH-PPV acts as a barrier while CdSequantum dots form the well layer. The devices exhibit negative differential resistance(NDR) at low voltages. For these devices, strong negative differential resistance is observedat room temperature. A maximum value of 51 for the peak-to-valley ratio of current isreported. Tunneling of electrons through the discrete quantum confined states in the CdSequantum dots is believed to be responsible for the multiple peaks observed in theI–V measurement. Depending on the observed NDR signature, operating mechanisms areexplored based on resonant tunneling and Coulomb blockade effects.

Optofluidic refractometer using resonant optical tunneling effect

This paper presents the design and analysis of a liquid refractive index sensor that utilizes a unique physical mechanism of resonant optical tunneling effect (ROTE). The sensor consists of two hemicylindrical prisms, two air gaps, and a microfluidic channel. All parts can be microfabricated using an optical resin NOA81. Theoretical study shows that this ROTE sensor has extremely sharp transmission peak and achieves a sensitivity of 760 nm∕refractive index unit (RIU) and a detectivity of 85 000 RIU(-1). Although the sensitivity is smaller than that of a typical surface plasmon resonance (SPR) sensor (3200 nm∕RIU) and is comparable to a 95% reflectivity Fabry-Pérot (FP) etalon (440 nm∕RIU), the detectivity is 17 000 times larger than that of the SPR sensor and 85 times larger than that of the FP etalon. Such ROTE sensor could potentially achieve an ultrahigh sensitivity of 10(-9) RIU, two orders higher than the best results of current methods.

Reflectionless tunneling of infrared radiation through subwavelength slit in a waveguide

A new effect of resonant tunneling of a fundamental mode of optical radiation through a subwavelength slit formed by smoothly shaped narrowing of a waveguide is examined. An effective energy transfer by evanescent waves is shown to be determined by the geometry of curvilinear narrowing. Spectra of reflectionless transmittance for waves 2.5–3 times longer than the width of the slit are found. Dependence of resonant tunneling on the geometrical parameters of narrowing and splitting of resonant maxima resulting in formation of two peaks of tunneling transmittance are demonstrated. An additional insight into the properties of narrowed waveguides has been obtained through the visualization of the variation of the field patterns associated with the modes for a specific configuration and the wavelength.

Schottky-Barrier Metal–Oxide–Semiconductor Field-Effect Transistors as Resonant Tunneling Devices

The current–voltage characteristics of double-gated Schottky-barrier metal–oxide–semiconductor field-effect transistor (MOSFET) 10 nm in length and with body thickness of 3 nm is numerically studied, illustrating a similarity between the rectangular quantum well cavity in conventional resonant tunneling diodes and the parabolic-like cavity created by a pair of Schottky junctions in scaled Schottky-barrier MOSFETs. Assuming ballistic transport for electrons within effective mass approximation, the appearance of negative differential resistance due to the resonant tunneling effect between the Schottky junctions of 0.75 eV height is confirmed by non-equilibrium Green's function simulation. In such scaled Schottky-barrier MOSFETs, the tunneling electrons by themselves determine the shape of resonant potential, through the charge terms in electrostatic field equations. Using both the Poisson equation and the Laplace equation, we highlight the importance of the self-consistency for realizing successful resonant tunneling operation in scaled Schottky-barrier MOSFETs.

Study of silicon quantum dots in a SiO 2 matrix for energy selective contacts applications

Structures consisting of a single layer of silicon quantum dots in silicon dioxide matrix represent a promising approach to implement energy selective contacts for hot carrier solar cells. The opening of the band gap and the resonant tunneling effect allow extraction of carriers within a narrow tunable range of energies. In this work, several silicon quantum dots double barrier structures have been realized using RF-magnetron co-sputtering. Quantum confinement properties of silicon quantum dots and the influence of the annealing process duration on crystallization have been investigated using photoluminescence measurements.

Tunneling Intensity Enhancement of Resonant Tunneling Effects Caused by Surface Plasmon Excitations

This study investigates whether the resonant tunneling intensity of one groove of a metal film with periodic grooves on both surfaces can be enhanced by adjusting the relative permittivity of adjacent grooves of the emitting plane. As the relative permittivity of the side grooves of the emitting plane increases, the emission intensity of the center groove first increases but eventually saturates. This property is mainly attributable to concentration of incident intensity in the center groove of the incident plane. Larger numbers of lumped grooves or larger distances between two adjacent grooves increases the intensity of light entering the system, which ultimately increases the intensity of emitted light. This enhanced emission intensity achieved by resonant tunneling effects has potential applications in future plasmonic transistor designs.

Preparation and characteristics of Cu/Al2O3/MgF2/Au tunnel junction

The fabrication process of Cu/Al2O3/MgF2/Au double-barrier metal/insulator/metal junction (DMIMJ) was introduced, and more stable light emission from this junction was successfully observed. The light emission physical mechanism of the junction was discussed. Results show that light emission spectrum of this structure locates at wavelength of 250–700 nm with two peaks at around 460 nm and 640 nm, which moves towards shorter wavelength region in comparison with that of the Al/Al2O3/Au junction. The light emission efficiency of this junction ranges from 0.7×10−5–2.0×10−5, which is 1 to 2 orders higher than that of the single-barrier Al/Al2O3/Au junction. The improved properties of this structure should be due to the electrons resonant tunneling effect in the double-barrier.

Research on double-barrier resonant tunneling effect based stress measurement methods

Piezoresistive effect of semiconductor materials is often used in microsensors as a sensing principle. Resonant tunneling diodes (RTDs) have been proved to have negative differential resistance effect, and their current–voltage characteristics change as a function of stress, which can be generated by external mechanical loads, such as pressures, accelerations and so on. According to this, the Meso-piezoresistive effect of RTDs can be used for stress measurement. This paper discusses two double-barrier resonant tunneling effect based stress measurement methods, including an RTD-Wheatstone bridge based method originally proposed. According to the results from the RTD-Wheatstone bridge based experiment, the piezoresistive sensitivity of RTD is adjustable in a range of 3 orders. And the largest piezoresistive sensitivity of RTD is larger than that of common semiconductor materials, such as silicon and GaAs.

Resonant tunneling effects on cavity-embedded metal film caused by surface-plasmon excitation

We investigate cavity-modulated resonant tunneling through a silver film with periodic grooves on both surfaces. A strip cavity embedded in the film affects tunneling frequencies via a coupling mode and waveguide mode. In the coupling mode, both the resonant tunneling through the gap between the groove and the cavity and the cavity itself form an entire resonant structure. In the waveguide mode, however, the cavity functions as a surface-plasmon waveguide. Hence, tunneling frequencies are close to resonant absorption frequencies of the groove structure and are irrelevant to cavity properties.