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Charge current and thermal spin-transfer torque (TSTT) in asymmetric double-barrier magnetic tunnel junctions (DBMTJs) with a non-magnetic metal (NM) spacer as CoFeB/MgO/NM/MgO/LSMO are studied by non-equilibrium Green’s function (NEGF) formalism. It is found that the results show oscillatory behavior with an increase of the NM spacer thickness due to the resonant tunneling effect through the DBMTJs structures. About the dependence of the temperature difference and angle between the magnetizations, the charge current and TSTT are larger at the specific thicknesses (resonant positions) of the NM spacer than the others. The results also illustrate a magnitude enhancement for asymmetric DBMTJs compared with asymmetric single-barrier MTJs (SBMTJs). Therefore, it is possible to achieve a large TSTT for magnetization dynamics by new asymmetric DBMTJs.

The substitution effect of a Ferro-magnet (FM) electrode by a half-metallic FM material La0.7Sr0.3MnO3 (LSMO) on charge current and spin-transfer torque (STT) components is studied in MgO-based double barrier magnetic tunnel junctions (DBMTJs) with a middle non-magnetic metal (NM) layer. Using non-equilibrium Green’s function (NEGF) formalism, it is observed that the current and STT components show oscillatory behavior due to quantum well states in the middle NM layer and resonant tunneling effect. We also study effect of difference in the thickness of the MgO insulators. Bias dependence demonstrate the magnitude enhancement of the current and in-plane STT in new asymmetric DBMTJs (A-DBMTJs) compared with symmetric DBMTJs (S-DBMTJs), however, perpendicular STT decreases in the A-DBMTJs. Results also show different behavior compared with conventional asymmetric MTJs and spin valves (SVs). Therefore, one can design new memory devices by means of suitable insulator and FM electrodes with proper thicknesses.

The effects of the off-set energy between the dielectric films which are formed at the both edges of the channel and the Si substrate on the electrical characteristics are examined for the Si resonant tunneling MOST (SRTMOST). The barrier height of the dielectric films has a great influence on the operation of the SRTMOST. The relationship between the transmission coefficient and the off-set energy of the double barrier/Si is calculated as well as the relationships between the gate-off currents, the transition time from the source to the drain and the off-set energy. It was found that the critical off-set energy of dielectric film/Si is approximately 1.0–1.5 eV.

Generalized-barrier parameters are studied theoretically for rectangular and trapezoidal single-barriers as well as parallel-plane ones, which are basic units for double-barrier and multiple-barrier structures. Analytical expressions for these parameters are derived by taking into account the position-dependent effective-mass effect. Furthermore, the expressions for the generalized-barrier parameters of optical single-layer thin film structures are considered and permit direct application of previous results to thin film interference filters also. The heights of resonant peaks and the resonance widths in asymmetrical double-barrier structures are studied as functions of the generalized-barrier parameters.

We have analysed the dimensionality of the emitter electron gas of double barrier devices (DBD) under bias and found evidence for the coexistence of both two- and three-dimensional (2D and 3D) electron gases. Magnetotunneling measurements performed on a series of n-type GaAs/(AlGa)As DBD with varying emitter doping profiles have shown that the electron gas may have a 2D and/or 3D character depending on the emitter doping level and on the applied bias. In devices with heavily doped emitter layers, electrons tunnel from 3D-states, whereas for lightly doped emitters a 2D-electron gas is formed in the emitter contact. For intermediary doping levels both 2D- and 3D-electron gases may coexist, depending on the applied bias.

Γ-X-Γ magneto-tunneling oscillations have been reported, to examine the influence of Γ-X mixing on the tunneling processes in asymmetrical double barrier structures (DBS). From the oscillatory period in the reciprocal magnetic field, the band offset between the X-valley in AlAs and the Γ-valley in GaAs has been evaluated to be very close to the commonly adopted value. Moreover, the well-developed oscillatory feature allows one to experimentally study the Γ-X coupling strength in a more quantitative manner.

We have investigated the peak and valley currents for a series of resonant tunneling diodes with AlAs barriers having widths in the range 1.9–5.9 nm and GaAs wells fabricated on GaAs substrates. Using a simple WKB expression that assumes resonant tunneling dominated by transfer through the Γ-Γ conduction band edge, a value for the strength, m b ∗ V b , of our AlAs barriers is found to be 0.069 ± 0.01 eV and the effective mass is found to be m b = (0.068 ± 0.01) m 0 . This agrees to within the measurement error with the result obtained for a series of diodes fabricated on InP by Broekaert et al . 1 with In 0.53 Ga 0.47 As wells and pseudomorphic AlAs barriers. The measured peak currents are compared with the results of self-consistent numerical solutions of Poisson's and Schroedinger's equations using the deduced effective mass.

We describe self-consistent calculations for the current-voltage characteristics of double barrier resonant tunneling diodes using two models representing extreme limits for the carrier equilibrium conditions outside the double barriers. We show that for SiGe double barrier diodes the model of Ohnishi et al.1 clearly gives closer agreement with experiment while for AlAsGaAs structures the model of Cahay et al.2 is more appropriate. Comparison of the two models gives insight into the role of scattering and thermal equilibrium in the regions adjacent to the double barrier in determining the current-voltage characteristics of these devices. The existence of an intrinsic bistability for these self-consistent calculations is confirmed.

The resonant tunnelling of photocreated holes in a double barrier structure, which was specially designed for spectroscopic studies, is investigated using photoluminescence. The effect of photocreated holes on the resonant tunnelling current, space charge build-up in the quantum well and the photoluminescence spectrum in an asymmetric double barrier structure as a function of excitation intensity is studied.

Magneto-tunnelling (B·J) is investigated in a symmetric double barrier resonant tunnelling device based on (InGa)As-(InAl)As. The effects of the Γ conduction band non-parabolicity are observed through the appearance of terms proportional to B3 and B4 in the dependence of Vp, the voltage at the current peak position of the I–V characteristics, on the magnetic field. A theoretical analysis considering pertubation theory and a simplified form of the formalism developed by Ekenberg [Phys. Rev. B40 , 7714(1989)] is done which is in qualitative agreement with the experimental results.

When the environment of a one-dimensional resonant double barrier acts as a source of dephasing or dissipation we find that the resonant half-linewidth is larger than the decay rate of a quasi-bound state. This result shows that measuring the decay rate of a quasi-bound state does not necessarily yield the resonant half-linewidth.

The infrared admittance of the Double Barrier Structure (DBS) is investigated by using a time-dependent quantum theory. The analysis is carried out under the small signal condition with no dc bias. The calculated results show conductance oscillations in the infrared frequency region. The oscillations are associated with the quantum well transit time resonances.

A theoretical formalism to study the current-noise characteristic of one-dimensional double barrier heterostructures taking into account correlation effects is developed within the context of the Keldysh nonequilibrium Green functions. The effects of the Coulomb blockade on the characteristic curve (current versus voltage) and on the current fluctuation are studied in a selfconsistent calculation. For the static case a reduction of the full shot noise is observed. The effects of the barrier characteristics on the transport properties are also analyzed. A connection between the noise frequency spectrum and the transit time of the electron going along the structure is established.

A theoretical analysis of the effect of scattering centers on tunneling current in amorphous (a-SiC:H/a-Si:H/a-SiC:H) double barrier heterostructures (DBH) is presented in terms of the transfer matrix and Airy function approaches. We consider one localized center in the well of the DBH and take into account the random distribution of its position by making configurational average. We use the δ-type function to describe the perturbation potential of the centers. In agreement with experimental observations, we find resonant peaks arising from quantized states in the well even in the case of the presence of scattering centers. The effect of scattering is to lower the transmission probability and to shift and broaden the peak of the resonant tunneling spectrum. For the I–V characteristics the effect of scattering is to shift the resonance shoulders.

Intrinsic bistability is observed in the current-voltage and capacitance-voltage characteristics of double-barrier resonant tunnelling structures. Analysis of the C(V) measurements and the magneto-oscillations in both I(V) and C(V) is used to determine the resonant charge build-up in the well which gives rise to the intrinsic bistability.

The effect of elastic scattering centers on the current-voltage (I–V) characteristics of double barrier resonant tunneling diodes with transverse confinement is examined. It is shown that elastic scattering centers break the separation of variables condition, and allow transitions between states of different transverse confinement. The changes to the transmission coefficients through the structure due to elastic scattering in the well of a resonant tunneling device are modeled by using perturbation theory. It is shown that additional structure in the I–V characteristics may result.