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A novel lattice matched double barrier Al 0.72 In 0.16 Ga 0.12 N/Al 0.18 In 0.04 Ga 0.78 N/GaN normally-off high electron mobility transistor (HEMT) is designed and simulated by solving a set of thermodynamic transport equations. Using the experimentally calibrated physical models with bearing mobility degradation by surface roughness in account, the recess gate and double barrier of the proposed device achieves a maximum drain current density ( $I_{D,max}$ ) of 1149 mA/mm and a maximum transconductance ( $g_{m,max}$ ) of 358 mS/mm with a positive threshold voltage ( $V_{th}$ ) of 0.2 V. The small polarization charge of first barrier is responsible for positive $V_{th}$ . $I_{DS,max}$ in the double barrier HEMT at high gate bias condition is due to injection of electrons from upper 2DEG which is almost impossible at lower gate voltage because of insufficient energy to cross the barrier. The injection of electrons is further supported by the second peak in the $\text{g}_{m}$ curve at low gate bias $V_{G} = 1\text{V}$ . The outcome of this study suggests that the proposed device will be beneficial for high-frequency and high-power electronic applications.

The use of hydrogen and helium as a fuel requires well-developed technologies for the separation of gas mixtures, in particular, separation of isotopes of an element. The presence of quantum effects makes such processes possible, and the proposed system of two potential barriers enhances the differences in the passage of isotopes through two layers of matter providing high separation efficiency. The probability of atoms passing through composite barriers is derived from the solving of stationary Schroedinger equation.

Glass-ceramics are well known for the excellent combination properties provided by their components, a glassy matrix and crystalline phases, and have promising applications in the immobilization and detoxification of solid waste containing toxic metals. Glass-ceramic products were successfully synthesized in CaO-MgO-SiO2-Al2O3 -Cr2O3 system. Two key measures--partitioning ratio of Cr in the spinel and Cr leaching ratio--were used to investigate the mechanism of Cr immobilization in the glass-ceramic products. The results of powder X-ray diffraction revealed that both spinel and diopside were major crystalline phases in the products. The value of x in the MgCr(x)Al(2-x)O4 spinel was highly related to the amount of Cr2O3 added to the glass-ceramic system. As Cr2O3 content increased, the proportion of spinel phase increased, while that of glass phase decreased. The partitioning ratio of Cr in spinel phase was about 70% for 2 wt.% Cr2O3, and increased to 90% when loaded with 10 wt.% of Cr2O3. According to the results of the prolonged toxicity characteristic leaching procedure, the Cr leaching ratio decreased with the increase of Cr partitioning ratio into the spinel phase. The findings of this study clearly indicate that glass-ceramic formed by spinel structure and residual glass successfully immobilized Cr.

Spin-polarized currents in double-barrier magnetic tunnel junctions (MTJs) as CoFeB/MgO/InP/MgO/CoFeB (MTJs-InP) are investigated by non-equilibrium Green’s function formalism. The asymmetric structures with a half-metal LSMO contact are studied and a spin-diode behavior is found compared to the MTJs-InP. Charge and spin currents as well as spin polarization as a function of bias voltage, angle between magnetizations and quantum-well thickness are also described. A nearly 100% spin polarization is observed at a certain range of bias voltage. Therefore, one can design excellent spin-filter devices based on new MTJs-InP.

This paper describes the physical simulation of Al0.3Ga0.7N/GaN-based double barrier resonant tunnelling diode (RTD) with cubic-GaN structure using Silvaco ATLAS. Cubic-GaN is interesting for vertical transport devices due to the absence of internal polarization. Proper selection of material parameters is vital in order to optimize the device performance. The relationship between current-voltage (I-V) characteristic, particularly the negative differential resistance (NDR) with respect to variation in barrier composition, well width and barrier thickness are studied in detail. RTDs with clear NDR are demonstrated with peak-to-valley-current ratio (PVCR) of 7.19 and peak current density of 3.77 mA/cm2 at room temperature. The optimum barrier thickness for a given composition is determined by using the ratio of current magnitude at resonant peak to the width of the resonance, and also used as figure of merit for the device. Finally, optimum parameters for the promising cubic Al0.3Ga0.7N/GaN RTD are proposed.

Thin film transistors with nanoparticles silicon floating-gate are fabricated by plasma enhanced chemical vapor deposition. It should be noted that SiO2acts as both a tunneling and a blocking layer. Meanwhile, some np-Si dots are embedded within SiO2layers. The electrical characteristic of the devices are measured by semiconductor parameter analyzer at room temperature. These Thin film transistors show a good device performance with a high charge-carrier mobility of 33 cm2/vs and a large on/off ratio of 1.2×106. Moreover, the capability of written and erasing was demonstrated. This indicates that thin film transistors can be operated as rewritable nonvolatile floating gate memory devices.

We study the tunneling of Dirac fermions in graphene through a double barrier potential allowing the carriers to have an effective mass inside the barrier as generated by a lattice miss-match with the boron nitride substrate. The consequences of this gap opening on the transmission are investigated. The realization of resonant tunneling conditions is also analyzed., Comment: 17 pages, 6 figures

Double barrier metal–oxide–semiconductor tunnel diodes with ultrathin PECVD Si and thermal SiO 2 layers were fabricated. The measured capacitance–voltage and current–voltage characteristics were interpreted and physical parameters of the structures were extracted by means of a theoretical model.

We evaluate the transmission and the conductance through double and triple non-uniform magnetic barriers in graphene-based nanostructures. The results indicate that non-uniform magnetic modulation results in rich transport properties. Compared with uniform double barrier magnetic structures, both the transmission and the conductance are drastically reduced through non-uniform ones. In the non-uniform triple magnetic barriers, the transmission and the conductance exhibit complicated oscillations, which vary with the width or the height of magnetic barriers. The non-uniformity introduced by altering the height and width of magnetic barriers have different effects on the transmission. For the magnetic barriers with different heights, the transmission is suppressed greatly in both low and high incident wave vector regions, while for the magnetic barriers with different widths, the obvious suppression occurs in the low incident wave vector region.

Ibuprofen (IBU) was chosen as a model drug to investigate the drug delivery rate. Mesoporous MCM-41 has been charged with ibuprofen (MCM-41_IBU). Calcium alginate was applied to encapsulate free drug and the mesoporous material. The system with double barrier demonstrated a slower release of IBU than free ibuprofen-loaded alginate beads and MCM-41_IBU. The IBU release from alginate matrix can be controlled by adjusting the free IBU/MCM-41_IBU ratio.

We have investigated the vertical electronic transport in AlN/GaN/AlN double barrier structures grown by plasma-assisted molecular-beam epitaxy, with AlN barrier thickness of 0.5 nm and a GaN well thickness varying from 0.5 nm to 2 nm. Two different current levels were observed in different devices in all the samples, the highest one being attributed to leakage through dislocations, and the lower one to tunnelling transport through the barriers. In the sample with a well thickness of 0.5 nm, we observed a bi-stable behaviour, with an apparent negative differential resistance in the current-voltage characteristic when scanning the voltage from negative to positive bias. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Double proton transfer reactions of pyrazole–guanidine species exhibit unusual energy profiles of a plateau form, different from the standard single and double barrier shapes. We have demonstrated earlier that this leads to a characteristically different quantum dynamical behavior of plateau reactions, when measured appropriately. Here we show that these differences also carry over to traditional measures of reaction probability.

We have investigated the tunneling magnetoresistance (TMR) in GaMnAs-based double barrier magnetic tunneling junctions (DB-MTJs) to clarify the origin of extremely low threshold current density for current-driven magnetic orientation reversal achieved in the systems. The TMR characteristics including minor loop behavior are well explained by assuming that three magnetic layers in the DB-MTJ have different coercive forces and that the uniaxial magnetic anisotropy in the middle magnetic layer is enhanced with decreasing the layer thickness. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Appearances and disappearances of Gd islands grown on top of a W(1 1 0) substrate were observed in time scales of hours after exposing the surface to a few Langmuirs of hydrogen. The phenomenon is presented and explained in terms of (temporary) creation of electrically floating islands, due to electrical decoupling of the island and substrate by the hydrogen that diffuses into the island/substrate interface. The disappearance of such an island is explained by forming a double barrier junction consisting of two tunneling barriers in series, causing, by charging, the potential of the island to become equal to that of the tip. The island then becomes “invisible” and the tip follows the corrugation of the surface under the substrate. The reappearance follows hydrogen mobility that retains the electrical conductivity of the island–substrate interface.

We report on the electrical characterization of AlN/GaN/AlN double-barrier resonant tunnelling diodes (RTDs) using steady-state current-voltage and capacitance-voltage (C-V) characteristics in a wide frequency range with 2 kHz steps. The C-V characteristics of a double-barrier RTD show different behaviour under forward and reverse polarities and a strong dependence on frequency. The monotonous growth of capacitance at forward bias was registered, while a more complicated dependence was observed at reverse voltages. In order to analyse this dependence, a self-consistent calculation of the potential profile of the structure was performed taking into account polarization effects at the AlN/GaN interfaces. The peculiarities are analysed in the model of possible charge trapping at the interface states. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The magnetic trapping potentials for atoms on atom chips are determined by the current flow pattern in the chip wires. By modifying the wire shape using focused ion beam nano-machining we can design specialized current flow patterns and therefore micro-design the magnetic trapping potentials. We give designs for a barrier, a quantum dot, and a double well or double barrier and show preliminary experiments with ultra cold atoms in these designed potentials.

We have modeled the optical properties of the ZnMgO/ZnO/ZnMgO system and correlated them to its transport properties by employing an effective mass equation method. By its construction our method was sensitive to the barrier thickness of the system. From our results we deduce that there are more states in the well than resonant tunneling peaks in the transport data. The “missing” states in the electrical characteristics are not seen because of their much lower localization in the well. However these states are responsible for the UV activity of the system. Reducing the barrier thickness changes dramatically the localization of the states in the well without affecting significantly the energy levels. Hence the electrical properties can be changed without changing significantly the optical properties.

It is shown, by solving numerically the time-dependent Schrodinger equation, that the resonant transmission of electrons through double barrier structures can significantly be modified and controlled by intense laser fields. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

GaN/AlGaN double barrier resonant tunnelling structures grown by molecular beam epitaxy on GaN templates have been studied. Peaks in the I(V) characteristics are observed, which are similar to resonant peaks seen in conventional III–V based devices. However, the behaviour of the peaks in I(V) depend upon the previous charge-state of the device produced by electrical bias. Current instabilities are also observed at low voltages. The possible origin of the peaks in the I(V) at room temperature and 4 K is discussed. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The efficacy of atmospheric plasma treatment on microbial decontamination of different kinds of food products is already known. Recently, new applications of this innovative technology have been proposed, in order to test the improvement of quality maintenance of minimally processed fruit and vegetables. Nevertheless, the knowledge on the modifications of functional and nutritional properties of minimally processed fruit is still scarce. The objective of this study was to evaluate the effect of atmospheric double barrier discharge (DBD) plasma treatment on the quality maintenance of fresh-cut kiwifruit. Treatments of 10 and 20 min per side were performed and their consequences were evaluated during four days of storage in controlled conditions by monitoring parameters related to visual quality, texture, chlorophyll, carotenoids and polyphenols. The in vitro antioxidant activity was evaluated through a multimodal approach, combining different assays for the analysis of antiradical activity and reducing activity of antioxidants. According to the obtained results, plasma treatments positively influenced the quality maintenance of the product, by improving colour retention and reducing the darkened area formation during storage, not inducing any textural change compared with the control. Plasma treatments caused an immediate slight loss of pigments, but a better retention during storage. No significant changes in antioxidants content and antioxidant activity were observed among treated samples and control ones.

The current-voltage characteristics for the double barrier resonant-tunneling structure incorporated into the depletion region of a Schottky barrier, are evaluated and analyzed. It is demonstrated that the Schottky barrier can block or unblock (depending on the parameters of the problem involved) the resonant-tunneling current effectively. Hence both a very sharp and strong enhancement of current through the structure considered takes place for forward bias.

We have studied experimentally the current-voltage characteristics of double-barrier Nb-Al-AlO/sub x/-Al-AlO/sub x/-(Al-)Nb junctions exposed to microwave radiation at 4.2 K. Both integer and fractional Shapiro steps were observed. A complicated behavior of the step heights was observed as a function of both the microwave power and an applied magnetic field. Reasonable agreement with the RSJ model was obtained only for the steps 0 to 2 observed in current-voltage characteristics of the junctions with a "clean" middle Al layer. A deviation from RSJ-like behavior was found for higher-order integer steps and fractional steps. Devices with a "dirty" middle Al layer displayed more significant deviation from RSJ-like behavior. Step heights vs. magnetic field dependences in some cases were found to be qualitatively different from the field dependence of the dc Josephson current.

New theoretical and experimental results on double-barrier SIS'IS Josephson junctions are presented (I is a tunnel barrier, S' is a thin film with critical temperature lower than that of S). The previously developed microscopic model for the stationary case, which describes the critical currents in Nb/Al/Nb junctions, is extended to the non-equilibrium regime of finite voltage. In particular, an intrinsic shunting resistance is estimated from I-V curves. We formulate the requirements for interface barriers in order to realize non-hysteretic SIS'IS junctions with high critical current density and I/sub c/R/sub N/ products. A comparison with single-barrier SIS junctions with high critical current density is carried out.

The present work computes the lifetime of the lowest resonant quasi-level in a GaAs–AlxGa1−xAs double-barrier structure based on the effective mass theory and takes into account the effective mass mismatch nature of well and barrier layers. The calculations showed a strong dependence of the lowest energy and its associated lifetime on both the effective masses of the well and barrier materials and aluminum concentration in the barrier AlxGa1−xAs material, which is associated to the barrier height. A comparison between a model based on different masses of well and barrier layers and another which considers same effective mass for both layers is made which showed a discrepancy of about 13% related to the lowest resonant energy and of about 29% associated to the resonant quasi-level lifetime both at barrier to well dimensions ratio of 6 and an aluminum composition of 0.45. The present work raises a question about the correct effective masses of tunneling carriers in resonant tunneling devices.

Double-barrier Nb/AlOx /Al/AlOx /Nb devices were fabricated and investigated in direct-current and alternating-current (ac) electromagnetic fields. The occurrence of current singularities and of the ac Josephson effect at T = 4.2 K are demonstrated. In a three-terminal configuration, a transistor-like behaviour of the structure is also observed.

We discuss the transmission coefficient τd in non-repetitive, one-dimensional, rectangular double-barrier structures without simplifications such as strongly attenuating barriers, strong localization, or overall constant effective tunneling mass of the electron. For resonance τd=1, we obtain two non-approximative conditions which require different resonance energies of the tunneling electron than previously reported in the literature. In fact, the resonance peaks are shifted to higher energy levels in the order of the width of the peaks due to the effect of non-constant tunneling mass. We investigate the dependence of the resonance condition and the shape of the resonance peaks in regard to perturbation of the electron energy, the gap width as well as the barrier width and height. Resonance is stable for variation of the barrier width but sensitive for variation of the barrier height and the gap width.

InAs quantum dots formed by submonolayer insertion of InAs into the GaAs quantum well of a GaAs/AlAs double barrier resonant tunnelling structure were studied. A series of sharp resonant tunnelling peaks in I–V characteristics of resonant tunnelling diodes with InAs insertions were observed. Temperature and magnetic field dependent I–V studies and theoretical modeling led us to conclude that these peaks are the result of resonant tunnelling through localized states associated with InAs quantum dots.

In this contribution we report on resonant tunneling in ZnSe/BeTe double-barrier structures. Vertical transport across the resonant-tunneling structure has been analyzed in detail as a function of temperature and applied magnetic field.

Discharge and ozone generation characteristics of a ferroelectric-ball and mica-sheet double barrier were investigated to study fundamentals of the barrier discharges and find out the optimal condition for efficient control of the pollutant gases. Five kinds of ferroelectric-balls, of which the dielectric constants are 33, 150, 660, 1500 and 1000, were investigated in atmosphere with various pulse frequencies of 0.2/spl sim/4.0 kHz. It is found that the double barrier has better discharge characteristics for ozone generation than those of a ferroelectric-ball single barrier and that ozone generation is greatly influenced by the dielectric constant of the ferroelectric-ball barrier and applied pulse frequency. As a result, there is an optimum condition of the dielectric constant and the applied pulse frequency to generate ozone effectively which are about E/sub r/=660 and frequencies higher than 4 kHz at the given experimental conditions.

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.

Using the transfer-matrix formalism, we investigate the tunneling of holes through symmetric double-barrier semiconductor structures with different heights of outer and inner edges. It is shown that, under appropriate conditions, a monotonic behavior (absence of resonant tunneling) occurs in the transmission coefficient in the absence or presence of the band mixing effect. Moreover, due to the band mixing effect, the monotonic behavior in all types of the transmission coefficient is only achievable when the resonant peak, related to the ground states of heavy holes in the corresponding potential well, disappears.

We report on resonant tunneling through ZnSe/BeTe double‐barrier, single‐quantum‐well structures. Negative differential resistance has been observed in the current–voltage characteristics up to room temperature. Due to a conduction‐band offset of more than 2 eV, four resonances with negative differential resistance could be detected for this semiconductor material combination at liquid‐helium temperature. The structures exhibit a peak‐to‐valley ratio up to 6:1 at 4.2 K. Current–voltage characteristics as a function of temperature have been studied and analyzed.

We report measurements of assisted tunnelling induced by non-equilibrium phonons in double barrier tunnelling devices in GaAs. The phonon signal has a peak at a bias voltage which depends linearly on phonon energy.

The authors are grateful for financial support by the state of Bavaria, the German Ministry of Education and Research (BMBF) within the national project HIRT (FKZ 13XP5003B). We present room temperature resonant tunneling of GaSb/AlAsSb double barrier resonant tunneling diodes with pseudomorphically grown prewell emitter structures comprising the ternary compound semiconductors GaInSb and GaAsSb. At room temperature, resonant tunneling is absent for diode structures without prewell emitters. The incorporation of Ga0.84In0.16Sb and GaAs0.05Sb0.95 prewell emitters leads to room temperature resonant tunneling with peak‐to‐valley current ratios of 1.45 and 1.36 , respectively. The room temperature operation is attributed to the enhanced Γ ‐L‐valley energy separation and consequently depopulation of L‐valley states in the conduction band of the ternary compound emitter prewell with respect to bulk GaSb. Postprint

Phonon‐assisted tunneling (PAT) has been studied in detail for two similar GaAs/AlAs double‐barrier structures. Calculations of the PAT current—including effects of optical‐phonon localization—are in good agreement with experimental data, and the emission rate for certain phonon types is found to depend sensitively on GaAs well width. We find that GaAs‐like modes clearly dominate in structures with wider wells, while GaAs and AlAs‐like modes contribute equivalently in narrower well structures. A simple overlap integral—involving the phonon potential and electronic wave functions—provides an effective selection rule for determining which types of phonons are preferentially emitted.

Specific difficulties of the fabrication of Nb/Al double-barrier junctions with high current density (10 kA/cm/sup 2/) and small area (1-3 /spl mu/m/sup 2/) are discussed and possible solutions are presented. The problem of nonuniform areas of the two superposed junctions was circumvented by introducing a loading effect in the etching process. Strong backbending of the I/V-curve was reduced by increasing the thickness of the Nb layer between the two superposed junctions. In a mixer experiment in the 100 GHz frequency band a broad-band response of the double-barrier device was obtained with a minimum receiver noise temperature of 45 K at 115 GHz. >

A subslab ventilation system was designed and installed in a high radon house in Brittany, France. Radon concentration in the basement of this house was reduced from an average 10 000 Bq/m 3 to less than 200 Bq/m 3 , thanks to a subslab depressurization system with a double barrier and a 32 W fan. Sealing the concrete slab cracks greatly improved the system performance. Finally, the feasibility of using a passive double barrier ventilation system is shown.

We examine two thermal reaction rates which can be defined for a one-dimensional model of a reaction dominated by a transient resonance. One of the rates corresponds to thermally equilibrated reactants in the region preceding the symmetrical double barrier potential supporting the intermediate complex. The other rate corresponds to pre-reaction thermal equilibration extending over the intermediate species. One rate is found to be twice the other. Numerical and analytical arguments are given to reach this conclusion. This discussion leads to a restrictive condition in the application of a formula given previously (R. Lefebvre and N. Moiseyev, J. Chem. Phys., 93 (1990) 7173) to relate the rate in the tunnelling regime to the set of artificial resonances produced by box quantization.

Wave-packet time-dependent quantum mechanics is used to calculate the tunneling probability through a double-barrier ZnSe/ZnTe structure. The time-dependent transmission characteristics are obtained for several structures, and detailed electron dynamics is presented. The resonant peaks due to the presence of the discrete energy levels in the quantum well as well as in the barrier region are observed.

The quantum effects of magnetic flux and in-plane electric field on an electron in a two-dimensional double-barrier nanoring have been studied. It has been found that the electronic structures and the related properties in the ring, such as the polarization, persistent currents, and far-infrared spectroscopy, can be tailored and controlled by the double barriers and the electric field. It may be useful for applications in quantum devices design in the future.

In this paper we present an electroluminescence study of electron populations in the quasiconfined excited states of two GaAs-AlGaAs double-barrier resonant tunnelling structures. We investigate the dependence of the electron population on both electron collector barrier width, which controls the electron tunnelling-out time, and on the confined level energy spacing, which controls the intersubband scattering time. We show that the observed excited state populations are in good agreement with the predictions of a rate equation analysis.

An illustrative analysis of the quasibound state using a complex reflection coefficient is presented. The global transfer matrix technique is formulated and used to evaluate the reflection coefficient. The quasibound state interacting with a half-space continuum is the well-known problem of a quantum well in an electric field and here it is called a quantum well mirror. The dependences of rectangular quantum well mirror and double barrier reflection coefficient on energy are compared. The wave functions are shown as well. A new way of finding the quasibound state energy and determining the quasibound state thickness based on the global transfer matrix behaviour is proposed. Eine illustrative Analyse des Quasibindungs-Zustandes, die den komplexen Reflexionskoeffizient verwendet, wird beschrieben. Die Globaltransfermatrix-Methode wird formuliert und fur die Bestimmung des Reflexionskoeffizienten verwendet. Die Wechselwirkung des Quasibindungs-Zustandes mil dem Halbraumkontinuum ist das bekannte Problem eines Potentialtopfes im elektrischen Feld und wird hier als Potentialtopfspiegel bezeichnet. Die Abhangigkeiten der Reflexionskoeffizienten des Potentialtopfspiegels und der Doppelbarriere von der Energie werden verglichen. Ebenso werden die Wellenfunktionen dargestellt. Ein neuer Weg fur die Bestimmung der Quasibindungs-Zustandsenergie und der Quasibindungs-Zustandsbreite wird vorgeschlagen, beruhend auf den Eigenschaften der Globaltransfermatrix.

The magnetocapacitive response of a double-barrier structure (DBS), biased beyond resonances, has for the first time been employed as a reliable method to determine the density of states (DOS) of two-dimensional (2D) electrons residing in the accumulation layer on the incident side of the DBS. Model calculations with a Gaussian-like DOS are compared with the experimental C versus B curves, measured at different biases and temperatures. The fitting is not only self-consistent but also remarkably good even in well-defined quantum Hall regimes. It is therefore evident that replacing a conventional gated heterostructure by a biased DBS makes it possible that the influence of the magnetoresistance of “lateral” 2D channel may be eliminated completely in the determination of the DOS, while the possible coexistence of three-dimensional (3D) electrons in the accumulation layer can easily be discriminated by experiments.

The novel Al 0.66 In 0.34 As 0.85 Sb 0.15 /In 0.53 Ga 0.47 As heterostructure has a large conduction band offset (about 1 eV). Taking the advantage of high conduction-band offset, it has been demonstrated to be a potential candidate for double-barrier resonant tunneling diodes (DBRTDs). Well width is an important parameter for the performance of a DBRTD. We fixed the barrier width and discussed the well width dependence for Al 0.66 In 0.34 As 0.85 Sb 0.15 /In 0.53 Ga 0.47 As DBRTD. Peak current densities exhibit a maximum at the 4 nm well width. A peak-to-valley current ratio of 46 with a peak current density of 22 kA/cm 2 at room temperature was demonstrated for the 4 nm-InGaAs-well.

The dc current in a biased double-barrier resonant-tunneling structure is calculated using a nonequilibrium Green's-function formalism. Realistic models involving well, barrier, and interface modes are employed to evaluate the phonon-assisted components of the current. The calculated dc current agrees well with experimental data for a GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As resonant-tunneling structure. The observed phonon-replica peak in the I-V characteristics is attributed to the emission of GaAs-confined modes in the well and AlAs-like symmetric interface modes. The effect of the nonequilibrium well-occupation function is shown to be small. For the ${\mathrm{In}}_{\mathit{x}}$${\mathrm{Al}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As/${\mathrm{In}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As resonant-tunneling structure, phonon scattering becomes comparable to alloy-well scattering at about 200 K.

In this paper we report the results of extensive magnetotransport experiments on asymmetric GaAs/AlAs double-barrier structures that were specifically designed to possess large phonon-assisted tunneling currents. We find quantitative agreement between measured valley currents at liquid-helium temperature and calculations that include the effects of phonon localization using the dielectric-continuum model. The results demonstrate that (1) a major part of the valley current in these structures is due to phonon-assisted tunneling, and (2) symmetric-interface phonons and confined phonons in the GaAs well are the most important in phonon-assisted tunneling processes

Resonant tunneling of an electron through a model Al0.5Ga0.5AsAlyGa1−yAsAl0.5Ga0.5As structure is investigated numerically using a transmission matrix approach. Our model considers the electric field, α in the well region only. This model is physically realized by changing Al-concentration continuously in the well region. Transmission coefficient is obtained as a function of incident electron energy for various α values. Tunneling characteristics (transmission coefficient vs voltage) are examined as a function of α. The effect of change in temperature is discussed.