Electron Resonant Tunneling Research Articles

Resonances in Fock space: optimization of a SASER device

We model the Fock space for the electronic resonant tunneling through a double barrier including the coherent effects of the electron–phonon interaction. The geometry is optimized to achieve the maximal optical phonon emission required by a SASER (ultrasound emitter) device.

Electron-spin polarization in magnetically modulated quantum structures

The spin-dependent electron resonant tunneling through magnetically modulated quantum structures has been investigated with and without an external electric field. The spin polarization is found to be strongly dependent on the magnetic configuration, the applied bias, the incident electron energy, and the incident wave vector. It is shown that an unpolarized beam of conducting electrons can be strongly polarized for an electron tunneling through magnetic-barrier structures, which is an arrangement with unidentical magnetic barriers and wells. The external electric field greatly changes the spin polarization of electrons for small electronic energies, where the electron-spin polarization exhibits considerable wave-vector-dependent features.

Spin-dependent delay time in electronic resonant tunneling at zero magnetic field

The dependence of the phase tunneling time on electronic spin polarization in symmetric and asymmetric double-barrier semiconductor heterostructures is studied theoretically. The effective one-band Hamiltonian approximation and spin-dependent boundary conditions are used for theoretical investigation of the electron spin influence on the delay time in tunneling processes. It is shown that the spin–orbit splitting in the dispersion relation for the electrons can provide a dependence of the delay time on the electron spin polarization without additional magnetic field. This dependence can be controlled by an external electric field and can be very pronounced for realistic double-barrier semiconductor heterostructures.

Secondary ion emission processes of sputtered alkali ions from alkali/Si(100) and Si(111)

The secondary alkali ion yield vs. the work function change (Δ φ) of Na, K and Cs/Si(100) and Si(111) was measured to discuss the details of secondary ion emission processes. In the case of alkali/metal systems, the secondary ion emission is explained by the electron tunneling model. In this model, the ionization of the ejected atom occurs as a result of electron resonant tunneling through the potential barrier separating an atom and a metal, and the secondary ion yield depends on exponentially the work function change of metal surface. For alkali/Si(100) systems, the secondary ion emission processes are explained in terms of the electron tunneling model since the secondary alkali ion yield vs. the work function change (Δ φ) follows the exponential manner. However, it is not easy to apply the simple electron tunneling model to our experimental results for alkali/Si(111) systems. There is the essential difference in surface structures between Si(100) and Si(111). Therefore, it is suggested that the local electronic environment around the adsorbates might be taken into consideration for alkali/Si(111) systems.

Monolithic integration of resonant interband tunneling diodes and high electron mobility transistors in the InAs/GaSb/AlSb material system

InAs/AlSb high electron mobility transistors (HEMTs) and resonant interband tunneling diodes (RITDs) with AlSb barriers and GaSb wells were grown in a single heterostructure by molecular beam epitaxy. The resulting HEMTs exhibit excellent dc and microwave performance at low drain voltages, with an intrinsic unity-current-gain cutoff frequency of 220 GHz. The RITD performance is comparable to RITDs grown directly on InAs substrates, with peak current densities above 104 A/cm2 and peak-to-valley ratios near 11 for 15 Å AlSb barriers. The results represent an important step toward the fabrication of high-speed, low-power logic circuits in this material system.

Observation of resonant tunneling through single self-assembled InAs quantum dots using electrophotoluminescence spectroscopy

The resonant tunneling through single InAs quantum dots embedded in an n-GaAs/i-Al0.38Ga0.62As/n-GaAs diode has been studied by using microscopic electrophotoluminescence spectroscopy. Many sharp luminescence lines which originated from single quantum dots were observed by injecting resonant electrons from the emitter to the dots. Bias dependence of a single luminescence line was investigated. The peak intensity showed triangular dependence which was similar to the current–voltage characteristics of electron resonant tunneling from three dimension to zero dimension. When the bias voltage was increased, the peak energy slightly shifted to a lower energy indicating the existence of Stark effect, and the linewidth slightly increased. The higher the luminescence energy was, the broader the linewidth was. This result agrees with the calculated resonant level width. The lifetime of resonant states was estimated to be 2.4–27 ps for luminescence linewidth of 250–22 μeV.

Magnetic Effects on Resonant Tunneling Through Quantum-Wire Arrays

We investigated the influences of a uniform and a nanoscaled periodic magnetic field on electron's resonant tunneling through quantum-wire arrays (QWA). It is shown that, due to the magnetic quantum-size effect and additional destructive interference induced by the nanoscaled periodic magnetic field, ballistic conductance spectrum for electron tunneling through the QWA is strongly modified; while for uniform magnetic modulation, it cannot modify the resonant structure of ballistic conductance.

Regulated and entangled photons from a single quantum Dot

We propose a new method of generating nonclassical optical field states. The method uses a semiconductor device, which consists of a single quantum dot as active medium embedded in a p- i- n junction and surrounded by a microcavity. Resonant tunneling of electrons and holes into the quantum dot ground states, together with the Pauli exclusion principle, produce regulated single photons or regulated pairs of photons. We propose that this device also has the unique potential to generate pairs of entangled photons at a well-defined repetition rate.

Stimulated resonant tunneling into quantum well excitons

Stimulated electron resonant tunneling into exciton states is investigated within the pairing approximation and the interacting boson approximation. The tunneling current saturates at large densities due to the fermionic nature of exciton constituents. Conditions under which stimulated tunneling can be observed experimentally are described.

Ultrafast electron dynamics at surfaces probed by resonant Auger spectroscopy

Ultrafast charge transfer processes from adsorbates to substrates are believed to occur on the timescale of (sub)-femtoseconds. In this paper we present experimental evidence for resonant tunneling of electrons at surfaces in the time regime ranging from <1 to ∼50 fs. The technique used to measure these ultrafast processes is based on high-resolution spectroscopy of the decay of core-excited states. We use the natural lifetime of the core-excited states, which is on the order of a few femtoseconds for the systems investigated, as an internal clock of the adsorbate systems.

SPIN EFFECT ON ENERGY SPECTRUM AND MAGNETOCONDUCTANCE IN A MAGNETIC QUANTUM ANTIDOT

By solving the single particle Shrdinger equation in different regions,we have discussed the spin effect on the energy levels of electron and the magnetoconductance in the magnetic quantum antidot. It is shown that the interaction of spin and the magnetic field results in the split of the energy levels. The splitting features are different from those in homogeneous magnetic field,i.e.the extent of the splitting is closely related to the angular momentum quantum number. Electron resonant tunneling to the magnetic edge states gives rise to the oscillations of the magnetoconductance. And spin-assisting magnetoconductance is quite different from that in the case where electron spin is ignored.There are more and shallower dips in the magnetoconductance spectrum for the former case.

Current oscillations in semiconductor-insulator multiple quantum wells

We examine theoretically the dc current-voltage characteristics of semiconductor-insulator multiple quantum wells with localized states in insulator barriers. The current exhibits periodic oscillating behavior for relatively high electric fields due to the resonant tunneling of electrons via these localized states. The time development of such current oscillations is also estimated.

Application of an AlGaAs/GaAs/InGaAs heterostructure emitter for a resonant-tunneling transistor

An AlGaAs/GaAs/InGaAs resonant-tunneling heterostructure-emitter bipolar transistor with negative-differential-resistance (NDR) behavior has been fabricated and demonstrated. Typical device performances with current gain of 140 incorporating an N-shaped NDR with a peak-to-valley current ratio of 5.3 are obtained at room temperature. The NDR behavior is believed to mainly result from a double-barrier-like resonant-tunneling effect. In other words, the on and off electron resonant tunneling from a depleted GaAs emitter through an InGaAs quantum well and ultrathin base toward a collector layer yield the interesting NDR behavior. Consequently, the proposed device provides a good potential for applications in amplifiers, low-power consumption, and logic currents.

Time dependence of resonant tunneling in heterostructures with a three-trough energy spectrum

The time dependence of resonant electron tunneling inGaAs andAlAs quantum heterostructures is studied for a three-trough model. From an analysis of transmitted and reflected wave phases, the spectra of tunneling and reflection times are obtained. The tunneling of a wave packet through a two-barrier heterostructure is modeled by numerical solution of the nonstationary Schrodinger equation.

Effects of structural disorders on sequential tunneling in multiple quantum wells

Based on an isotropic random distribution model, the effects of structural disorders embedded in the barriers on the sequential electron tunneling in multiple quantum wells were studied at low temperatures. By using a sequential tunneling model [Stievenard et al., Appl. Phys. Lett. 61 (1992) 1582], the transmission coefficient through a single barrier was calculated using a finite-difference method and averaged over random configurations of disorders. To compute the tunneling current, a self-consistent calculation for the electronic states was performed, including the Hartree and exchange interactions and non-parabolic energy dispersion. Both disorder-assisted and disorder-impeded electron tunneling phenomena were found as a function of the activation energy. The effects of electric field, barrier width, and temperature were also studied. The predicted resonant disorder-assisted electron tunneling should be large enough to be observable at low temperatures in an experiment.

Electron-spin polarization by resonant tunneling

The spin-dependent electron resonant tunneling through nonmagnetic III--V semiconductor asymmetric double barriers is studied theoretically within the envelope function approximation and the Kane model for the bulk. It is shown, in particular, that an unpolarized beam of conducting electrons can be strongly polarized, at zero magnetic field, by a spin-dependent resonant tunneling, due to the Rashba mesoscopic spin-orbit interaction. The electron transmission probability is calculated as a function of the electron's energy and angle of incidence. Specific results for tunneling across lattice matched politype ${\mathrm{Ga}}_{0.47}{\mathrm{In}}_{0.53}\mathrm{As}$/InP/${\mathrm{Ga}}_{0.47}{\mathrm{In}}_{0.53}\mathrm{As}$/${\mathrm{GaAs}}_{0.5}{\mathrm{Sb}}_{0.5}$/${\mathrm{Ga}}_{0.47}{\mathrm{In}}_{0.53}\mathrm{As}$ double barrier nanostructures show, for instance, sharp spin-split resonances, corresponding to resonant tunneling through spin-orbit split quasibound ground and excited electron states (quasisubbands). The calculated polarization of the transmitted beam in resonance with the second quasisubband shows that polarization bigger than 50% can be achieved with this effect.

Resonant electron tunneling in single quantum well heterostructure junction of electrodeposited metal semiconductor nanostructures using nuclear track filters

We report on resonant electron tunneling through a Cu–Se heterostructure junction grown electrochemically in the submicron size pores (0.8 μm) of a nuclear track filter (Polycarbonate). The prominent feature of negative differential resistance (NDR) has been observed in the current–voltage ( I– V) characteristic of the so-fabricated array of resonant tunneling diodes (RTDs) even at room temperature, along with a significant peak to valley current ratio (2.5) of the resonance. Tunneling structures of the nanofabricated RTDs around zero bias are also observed at room temperature. Our results show that the low cost and relatively easy electrodeposition method can be a very effective way to prepare resonant quantum tunneling devices, using the pores of nuclear track filters.

Observation of Resonant Photon Tunneling in Photonic Double Barrier Structures

Reflectance and transmittance of 632.8 nm He-Ne laser light for photonic double barrier structures (consisting of a SF10 prism, SiO2 layer, Al or Al2O3 active layer, SiO2 layer and SF10 prism) were measured as a function of the angle of incidence for both the ρ- and s-polarized incidence. Sharp reflection dips and transmission peaks were observed at angles larger than the critical angle of total reflection. The appearance of the transmission peaks can be attributed to resonant photon tunneling through the photonic double barrier structures analogous to resonant electron tunneling through double potential barrier structures. Resonant tunneling is mediated by the long-range surface plasmon polariton in the case of the Al active layer and the electromagnetic guided modes in the case of the Al2O3 layer.

One-dimensional to one-dimensional electron resonant tunneling in a double asymmetric quantum-wire structure

An atomically precise double asymmetric quantum-wire structure was fabricated with the cleaved edge overgrowth method. A resonant tunneling diode for such a structure was successfully achieved. Its voltage–current characteristic was measured at 77 K. A sharp resonant tunneling current peak was observed and its peak-to-valley ratio is about 18:1, which is much larger than that of a double-barrier quantum-well structure, and it is ascribed to one-dimensional to one-dimensional electron resonant tunneling through the double asymmetric quantum-wire structure.

Carrier density effects on the exciton binding energy in double quantum well systems

Carrier density effects on the dynamics of an electrically pumped exciton, created by hole-assisted, electron resonant tunneling in an asymmetric coupled quantum well system, has been studied self-consistently. Calculations show that, first, the binding energy and the oscillation period decrease with increasing carrier concentration, the charge oscillation being nonperiodic for sheet densities greater than 5×1010cm−2 (for the proposed sample). Second, a transition from excitonic to electron–hole plasma states occurs at densities ranging from 5×108 to 2.5×1010cm−2. As a consequence, the present work shows that many-body effects are necessary to obtain accurate results in calculating tunneling electromagnetic radiation.