Study Of Resonant Tunneling Research Articles

Coherent Resonant Tunneling through Double Metallic Quantum Well States.

Study of resonant tunneling through multimetallic quantum well (QW) structure is not only important for the fundamental understanding of quantum transport but also for the great potential to generate advanced functionalities of spintronic devices. However, it remains challenging to engineer such a structure due to the short electron phase coherence length in metallic QW system. Here, we demonstrate the successful fabrication of double-QW structure in a single fully epitaxial magnetic tunnel junction (MTJ) heterostructure, where two Fe QW layers are sandwiched between three MgAlO x tunnel barriers. We show clear evidence of the coherent resonant tunneling through the discrete QW states in the two QWs. The coherent resonant tunneling condition is fulfilled only when the middle barrier between the two QWs is thin enough and available QW states are present simultaneously in both QWs under a certain bias. Compared to the single QW structure, the resonant tunneling in double-QW MTJ produces strong conductivity oscillations with much narrower peak width (about half) owing to the enhanced energy filtering effect. This study presents a comprehensive understanding of the resonant tunneling mechanism in MTJ with multiple QWs, which is essential for future development of new spintronic devices operating in the quantum tunneling regime.

Study of resonant tunneling in Au nanoclusters on the surface of SiO2/Si thin films using the combined scanning tunneling microscopy and atomic-force microscopy technique

The morphology and electronic properties of Au nanoclusters on the surface of SiO2 thin films on n+-Si substrates are studied using the combined scanning tunneling microscopy (STM) and atomic-force microscopy (AFM) technique. The peaks associated with the resonant tunneling of electrons from the states of the valence band of the probe material to the states of the conduction band of the substrate material through Au nanoclusters are observed on the current-voltage characteristics for the contact of a p+-Si AFM probe with Au nanoclusters. Experimental results are interpreted by calculating the tunnel transparency of the SiO2/Au/SiO2 double barrier structure in a strong electric field.

Observation of resonant tunneling through a self-assembled InAs quantum dot layer

We report on the study of resonant tunneling through a self-assembled InAs quantum dot (QD) layer using the following design: The QD layer surrounded by undoped GaAs barriers is clad by two GaInNAs∕GaAs short-period superlattice regions which serve as injector and collector of electrons. A clear observation of three- to zero-dimensional resonant tunneling is presented in electrophotoluminescence measurement results and supported with current-voltage and capacitance-voltage characteristics.

Resonance Condition in Asymmetrical Rectangular Double-Barrier Structures with Deep Well

A theoretical study of resonant tunneling is carried out for asymmetrical rectangular double-barrier structures with a deep well. Analytical expressions for the transmission coefficient and the resonance condition are derived for the first time. The resonant tunneling with unity transmission (unity resonance) occurs when both the phase difference condition for resonance (PDCR) and the maximum condition for peak value (MCPV) hold simultaneously; under-unity resonant tunneling occurs so that the peak value of the transmission coefficient at resonance is below unity when only PDCR holds. Wave functions of an electron at the resonance level are calculated and the confining phenomenon is confirmed. Moreover, the peak value variation of the resonant transmission coefficient under an applied field is discussed.

Resonant tunnelling in asymmetrical double barrier structures complex coordinate approach

The complex coordinate approach of theoretical atomic spectroscopy is applied to the study of resonant tunnelling in (Ga,In)As/(Al,In)As-based asymmetrical double-barrier heterostructures within applied electric field. The method yields complex eigenvalues E = Er − iΓ/2 of the Hamiltonian matrix evaluated in a normalizable basis, where Er is the resonant energy and τ = ħ/Γ is the tunnelling lifetime. The dependence of Eres on the field and barrier asymmetry is discussed.

Theoretical study of resonant tunneling in symmetrical rectangular triple-barrier structures with deep wells

Resonant tunneling is studied theoretically in rectangular triple-barrier structures with deep double wells. Analytical expressions for the transmission coefficient and the resonance condition are derived. Transmission characteristics vs. electron energy are investigated and the boundary between the unity resonance and the under-unity resonance is examined. It is shown analytically that the transmission spectrum is a Lorentzian in form near energies of resonance. Moreover, wave functions of an electron at the resonance level are examined and the confining phenomena are studied.

Resonant tunneling and confining phenomena in symmetrical rectangular triple-barrier structures with c-type deep wells

Theoretical study of resonant tunneling is carried out in rectangular triple-barrier structures with C-type deep wells. Analytical expressions for the transmission coefficient and the resonance conditions are derived. Transmission characteristics versus electron energy are investigated and it is shown analytically that the transmission spectrum is a Lorentzian in form near energies of resonance. It is confirmed that the resonance energy is almost equal to the eigenenergy of the double-well structure. Moreover, wave functions of an electron at the resonance level are examined and the confining phenomenon is studied.

Quantum Dynamical Simulation of Many Electron-Phonon Coupled Systems on Parallel Computers

ABSTRACTA quantum dynamical simulation method is developed to investigate coupled many electron-phonon systems. Both electron and phonon wave functions are numerically propagated in time. The method is applied to the study of resonant tunneling of an electron through double quantum dots. Phonon-induced electron localization is observed. The space- splitting Schrödinger solver and dynamical-simulated-annealing Poisson solver are implemented on an 8,192-node MP-1 computer from MasPar.

Selection-rule breakdown in coherent resonant tunneling in a tilted magnetic field.

We report on a study of resonant tunneling in a magnetic field tilted with respect to the current direction on a double-barrier structure. A splitting of the resonant current peak into several satellites is observed and corresponds to tunneling with nonconservation of the Landau-level index. We propose a simple coherent-tunneling model that accounts very well for both positions and magnitudes of the observed features, and we show that these experiments clearly evidence new selection rules for tunneling in a tilted magnetic field.

Theoretical study of resonant tunneling in rectangular double-, triple-, quadruple-, and quintuple-barrier structures

The transmission coefficient and the resonance condition in the one-dimensional rectangular double-, triple-, quadruple-, and quintuple-barrier structures are derived theoretically under the assumption of the constant tunneling effective mass. It is found that the resonance energies are different from the eigenvalues in the quantum well due to coupling between wells in the multiple-barrier (much more than triple-barrier) structures. It is confirmed that the transmission spectrum is a Lorentzian near to energies of resonance.

A study of resonant tunneling in a 3-terminal ballistic device

Preliminary results are presented for a 3-terminal device fabricated by incorporating a narrow quantum well into the collector barrier of a unipolar hot electron transistor. The structure allows unique studies of the mechanism of resonant tunneling in which the carrier injection energy and the bias across the double barrier can be independently varied. The transistor clearly shows an additional current collection threshold representing as much as 10% of the injected current attributable to tunneling via the single subband in the quantum well. This interpretation is confirmed by measurements in perpendicular and parallel magnetic fields despite the fact that theoretical estimates of the resonant tunneling current without scattering are many orders of magnitude smaller, and there are strong indications that elastic scattering in the well is responsible for the enormous discrepancy. The data tend to support proposals (Guéret, 1989a, 1989b; Wolak, 1988) that elastic scattering is responsible for the large valley currents in resonant tunneling diodes, and it appears that the tunnel process may not be completely incoherent as has frequently been assumed up to now.