Resonant Tunneling Structures Research Articles

Transport properties of the resonant tunneling structures based on the pseudospin-1 Dirac–Weyl fermions

Transmission, conductivity, and shot noise are investigated in multi-barrier resonant tunneling structures based on the pseudospin-1 Dirac–Weyl model. Super Klein tunneling, perfect transmission plateau, and resonant tunneling collectively contribute to the transport properties. While resonant tunneling occurs when the energy of the passing quasiparticle coincides with the discrete quasibound energy level of the multi-barrier structure and is widely observed in parabolic and Dirac-cone-shape dispersive materials, super Klein tunneling and perfect transmission plateau are unique in pseudospin-1 systems and barrier-structure independent. As a result, the conductivity and shot noise in pseudospin-1 resonant-tunneling multi-barrier structures demonstrate remarkably different properties from their counterparts of both parabolic-dispersion semiconductors and pseudospin-1/2 Dirac–Weyl materials, typically graphene. It is found that the zero conductivity minimum remains for multi-barrier structures and the relative shot noise indicated by the Fano factor in the three-barrier system is larger than that in the double-barrier system when the Klein tunneling effect weakens.

TCAD Simulation Studies on Ultra-Low-Power Non-Volatile Memory.

Ultra-Low-Power Non-Volatile Memory (UltraRAM), as a promising storage device, has attracted wide research attention from the scientific community. Non-volatile data retention in combination with switching at ≤2.6 V is achieved through the use of the extraordinary 2.1 eV conduction band offsets of InAs/AlSb and a triple-barrier resonant tunnelling structure. Along these lines, in this work, the structure, storage mechanism, and improvement strategies of UltraRAM were systematically investigated to enhance storage window clarity and speed performance. First, the basic structure and working principle of UltraRAM were introduced, and its comparative advantages over traditional memory devices were highlighted. Furthermore, through the validation of the band structure and storage mechanism, the superior performance of UltraRAM, including its low operating voltage and excellent non-volatility, was further demonstrated. To address the issue of the small storage window, an improvement strategy was proposed by reducing the thickness of the channel layer to increase the storage window. The feasibility of this strategy was validated by performing a series of simulation-based experiments. From our analysis, a significant 80% increase in the storage window after thinning the channel layer was demonstrated, providing an important foundation for enhancing the performance of UltraRAM. Additionally, the data storage capability of this strategy was examined under the application of short pulse widths, and a data storage operation with a 10 ns pulse width was successfully achieved. In conclusion, valuable insights into the application of UltraRAM in the field of non-volatile storage were provided. Our work paves the way for further optimizing the memory performance and expanding the functionalities of UltraRAM.

Field emission in vacuum resonant tunneling heterostructures with high current densities

We analyse the steady-state thermal regime of a one-dimensional triode resonant tunnelling structure. The high currents generated by resonant tunnelling produce a large amount of heat that could damage the structure. Establishing the conditions under which it can operate at optimum efficiency is therefore a problem of great relevance for applications. The tunnel current is found via eigenvalues of the Schrödinger equation in quantum wells. By calculating the current generated in the device and using the energy conservation law in the electrodes, the temperature reached is obtained for different types of electrodes and the importance of heat conduction and thermal radiation is analysed. In the cases discussed, conduction is dominant. When the electrode material is copper, the temperature reached is similar to that of the thermostat for a wide range of electrode lengths, whereas when the cathode material is diamond-graphite and the anode material is copper, the temperature increases significantly as a function of length. The results obtained allow the temperature to be controlled for optimum performance of the field-emitting triode structures.

Bistability of AlGaAs/GaAs Resonant-Tunneling Diodes Heterostructural Channel.

This paper presents an effective compact model of current transfer for the estimation of hysteresis parameters on the volt-ampere characteristics of resonant-tunneling diodes. In the framework of the compact model, the appearance of hysteresis is explained as a manifestation of internal bistability due to interelectronic interaction in the channel of the resonant-tunneling structure. Unlike the models based on the method of equivalent circuits, the interelectronic interaction in the compact model is taken into account using the concentration parameter. Model validation allowed us to confirm the high accuracy of the model not only at the initial section of the volt-ampere characteristics, but also at the hysteresis parameters traditionally predicted with low accuracy, namely the loop width (∆ < 0.5%) and contrast (∆ < 7%). Thus, it is concluded that the models are promising for integration into systems for synthesizing the electrical characteristics of resonant-tunneling diodes.

Defect formation in InGaAs/AlSb/InAs memory devices

ULTRARAMTM is a novel floating-gate nonvolatile memory in which the oxide barrier of flash is replaced by a triple-barrier resonant tunneling structure comprising of multiple InAs/AlSb heterojunctions. The quality of the triple barrier resonant tunneling heterostructure of an ULTRARAMTM device in terms of interface sharpness and the presence of defects was analyzed by cross-sectional scanning tunneling microscopy. We observed two different types of defects: stacking faults originating in the layers below the triple barrier resonant tunneling structure and AlSb accumulations at the interface between the lower AlSb layer of the triple barrier resonant tunneling structure and the InGaAs channel. The InGaAs surface of a second sample was measured by atomic force microscopy in order to investigate whether its unevenness is caused by deposition of the AlSb layer or it is already present before the AlSb deposition process.

A Compact Current-Transfer Model in Resonant-Tunneling Structures with Consideration of Interelectronic Interaction

A compact analytical model of current transfer was developed to estimate the characteristics of heterostructured devices. The absence of empirical correction factors and the explicit accounting of the interelectronic interaction differentiates it from previous similar models. The model obtains an estimates of the electron density in the quantum well of the heterostructural channel and applies a self-consistent correction for resonance levels. It also provides accuracy in the positive differential resistance region of the I–V characteristics in the AlGaAs structures, with an average relative error not exceeding 2%. The time complexity of the calculations of the I–V characteristics using this model is several orders of magnitude less than that of calculations using ab initio models. Its high accuracy and low temporal complexity of calculations of I–V characteristics allow this model to be integrated in systems for the design and calculation of reliability indicators for devices, including terahertz devices.

Goos–Hänchen shift of a light beam tunable by graphene in the resonant optical tunneling structure

The structure for implementing resonant optical tunneling effect is a simple layered system of dielectrics that provides full light transmission for resonance condition, despite the presence of barrier layers partially locking light. The presence of a sharp resonant peak both for the intensity and for the spatial shift of the transmitted light beam makes such a structure promising for the creation of sensors and light control devices. This paper focuses on the spatial shift called the Goos–Hänchen shift of such a structure with interfaces of the waveguide layer coated by graphene. The effect of Goos–Hänchen shift near the resonance in this case may be controlled by small changes in the chemical potential or the Fermi energy of graphene, which can be controlled both chemically and by electrical bias. The characteristics of transmitted light beam strongly depend on the beam width for the selected optimal focusing condition.

Perfect transmission of the ultrarelativistic quasielectrons in pristine graphene

Within the framework of the Landauer-Buttiker formalism, the conductivity of one- and two-barrier graphene structures is calculated. The conditions for formation of the maximum value of the conductivity depending on the energy of ultrarelativistic quasielectrons as well as on the parameters of these structures (the values of Fermi velocity in different regions and the potential barriers height) are analyzed. It is believed that there is an electrostatic barrier and also the Fermi velocity barrier due to the fact that this quantity may aсquire different values in the barrier and out-of-barrier regions of the considered structures. The obtained expression for the transmission rates accounts for the π phase change of the transmitted wave function (which was not taken into consideration in the known formulae for the transmission rates of some papers). Consideration of this phase change leads to some new important features which characterize the transmission process in the graphene structures. We are the first to show that the effect of the supertunnelling manifests itself in graphene and it is observed both in the dependences of the transmission rates and of the conductivity on the quasielectron energy. This effect consists in the fact that, under certain conditions, the transmission through the structure is perfect (transmission rates T = 1) for the arbitrary angle of incidence of quasielectrons on the barrier. The expression іs given that determines the specified conditions for the supertunneling. The analysis of the transmission dependence on the problem parameters is also provided. • All-angled perfect tunneling can be observed in the graphene-based single barrier resonant-tunneling structure. • This type of tunneling significantly affects the conductivity of the given structure. • The analogous effect manifests itself also in the graphene based double barrier resonant-tunneling structure.

Tunneling transport in open nitride resonant tunneling structures taking into account the acoustic phonons: An variational approach

Quantum-mechanical theory of tunneling transport through open nanostructures based on nitride semiconductors, taking into account the contribution of acoustic phonons, is proposed. A variational method taking into account the component of Hamiltonian due to the deformation potential of acoustic phonons at different temperatures is developed. On the basis of the developed theory the transmission coefficient of a two-barrier AlN/GaN resonant tunneling nanostructure, its electronic conductivity and tunneling current are calculated taking into account the impact of acoustic phonons. It was found that with the increase of temperature values the frequencies of quantum transitions between electronic quasistationary states increase, an increase in temperature from cryogenic to room values results in a shift of the tunneling current peak and a decrease in the maximum value of dynamic conductivity in almost seven times.

Forming a Portion of Negative Differential Conductivity in the I–V Characteristic of Resonant-Tunneling Structures

Forming a Portion of Negative Differential Conductivity in the I–V Characteristic of Resonant-Tunneling Structures

Excitons in resonant tunnelling structures based on AlN/GaN/AlN/AlGaN/AlN nitride: spectral dependences and intensities of interband optical transitions

Excitons in resonant tunnelling structures based on AlN/GaN/AlN/AlGaN/AlN nitride: spectral dependences and intensities of interband optical transitions

Direct observation of resonant tunneling in heterostructure with a single quantum well

A resonant-tunneling conductivity was experimentally registered in a doped heterostructure with a single quantum well using admittance spectroscopy. Earlier, this effect was only realized in artificially created resonant tunneling structures, having four heterojunctions. A heterostructure with an In0.3Ga0.7As/GaAs quantum well was examined in the temperature range of 10–300 K. In admittance spectra, a competition of thermionic and tunneling escape mechanisms was noticed with a non-exponential Arrhenius plot. By means of numerical self-consistent simulations in a quantum box, we have shown the role of a quasi-bound level in resonant tunneling of electrons; in addition, the energies and wave functions of the quasi-bound state were derived in dependence on an applied bias. The modification of a transparency coefficient for a two-barrier Hartree potential as a function of the quantum well width and in dependence on the applied bias was also calculated. The resonant state took place only at symmetric barriers and disappeared, when the electric field tilted the barriers. The results can be used to develop a new type of resonant tunneling diodes and as a method for diagnostics of the tunnel effect in semiconductors.

Peculiarities in optical response of hybrid-barrier GaSb/InAs/AlSb resonant tunneling diode structure

We present comprehensive investigation of the optical properties of hybrid-barrier GaSb-based resonant tunneling structures, containing a bulk-like GaInAsSb absorption layer and two asymmetric type II GaSb/InAs/AlSb quantum wells. Methods of optical spectroscopy by means of Fourier-transformed photoluminescence and photoreflectance are employed to probe optical transitions in this complex multilayer system. Based on the comparison between the absorption-like and emission-like spectra (also in function of temperature) confronted with band structure calculations four main transitions could be resolved and identified. For one of them, there has been observed unusually strong linear polarization dependence never reported in structures of that kind. It has been interpreted as related to a transition at the GaSb/GaInAsSb interface, for which various scenarios causing the polarization selectivity are discussed.

Controlling Phase‐Coherent Electron Transport in III‐Nitrides: Toward Room Temperature Negative Differential Resistance in AlGaN/GaN Double Barrier Structures

AbstractResonant tunneling of electrons is important for the manufacture of high‐speed electronic oscillators and the electron injection control in quantum cascade lasers. In this work, room temperature negative differential resistance (NDR) in AlGaN/GaN double barrier structure with AlN/GaN digital alloy (DA) barriers is demonstrated. The peak‐to‐valley current ratio (PVCR) ranges from 1.1 to 1.24 at room temperature and becomes 1.5 to 2.96 at low temperatures, whereas no NDR is observed in double barrier structures with conventional ternary AlGaN barriers. The room temperature NDR together with the high PVCR at low temperature is attributed to the suppression of alloy disorder scattering by introducing AlN/GaN DA barriers. This work presents the successful control of phase‐coherent electron transport in III‐nitride heterostructures and is expected to benefit the future design of nitride‐based resonant tunneling structures and high‐speed electronic devices.

Edge effects for the light beam transmission through the resonant optical tunneling structure: Analytical theory

The resonant optical tunneling effect (ROTE) is a special phenomenon of complete light transmission through a layered structure with overcoming optical barriers, partially locking the light. The presence of a sharp resonant peak makes ROTE structures promising for creating optical sensors and switching optical devices. In many studies, the theoretical analysis of the light transmission through ROTE structures is limited to the approximation of plane waves, which narrows the understanding of the effect. The presented analytical theory allows explicitly establishing the outgoing electromagnetic field distribution for an arbitrary light beam, incident on the ROTE structure, within acceptable approximations. The theory application for a simple Gaussian beam is demonstrated. Changes in the resonant effect characteristics depending on the beam parameters may be significant.

Coherent electron quantum transport in hbox {In}_{0.53}hbox {Ga}_{0.47}As/GaAs_{0.51}hbox {Sb}_{0.49} double barrier resonant tunnelling structures

In this work, we have modelled and computed the transport properties of the double-barrier InGaAs/GaAsSb structure from the resonant tunnelling point of view. Based on the classical Tsu-Esaki formula for the tunnelling current, we have calculated the current density-voltage characteristic of a Al-free type-II hbox {In}_{0.53}hbox {Ga}_{0.47}hbox {As/GaAs}_{0.51}hbox {Sb}_{0.49} structure at different cryogenic and elevated temperatures. The tunnelling coefficient has been calculated in the framework of effective mass approximation with nonparabolicity included, using the transfer matrix approach. A good qualitative agreement of the position of resonant current peaks with the existing experimental data was achieved. Our calculation shows a very high sensitivity of the tunnelling current peak on monolayer-scale layer structure fluctuation which strongly affects peak to valley ratio in the resonant tunnelling structure.

Acoustic phonons in multilayer nitride-based AlN/GaN resonant tunneling structures

The study of physical processes associated with acoustic phonons in nitride-based nanosystems is of great importance for the effective operation of modern nanoscale devices. In this paper, a consistent theory of acoustic phonons arising in multilayer nitride-based semiconductor resonant tunneling structures, that can function as a separate cascade of a quantum cascade laser or detector is proposed. Using the physical and geometric parameters of a typical nanostructure, the spectrum of various types of acoustic phonons and the corresponding normalized components of the elastic displacement vector are calculated. It has been established that the spectrum of acoustic phonons of a multilayer nanostructure consists of two groups of the shear phonons dependencies and three groups of dependencies for a mixed spectrum of flexural and dilatational phonons. The dependencies of the acoustic phonons spectrum of the nanostructure and the components of the elastic displacement vector on its geometric parameters are studied. It has been established that for the components of the displacement vector u2 for shear phonons have a decrease in the absolute values of their maxima with increasing of energy level number. The components u1 and u3 of flexural and dilatational phonons behave respectively as symmetric and antisymmetric functions relatively the center of an separate selected layer of the nanostructure. The proposed theory can be further applied to study the interaction of electrons with acoustic phonons in multilayer resonant tunneling structures.

On the quaternionic form of the Pauli–Schrödinger equation

A thorough approach to quantum mechanics should rely on an algebraic operation of multiplication based on proper algebraic structures, i.e. division algebras. Quaternions, with their commutation rules isomorphic to SU(2), offer such a framework. In this work, a quaternion algebraic approach derived from the finite groups is used to solve the spatially invariant time-dependent Pauli–Schrödinger equation and derive the Rabi formula and the principle of nuclear magnetic resonance and its generalization. The spatial and time-dependent Pauli–Schrödinger equation is then written using left-chirality quaternions, i.e. by expressing the Pauli spinor, its time derivative, and the Hamiltonian as elements of the same division algebra. The quaternion formalism is used to derive the dispersion relation of a free electron and of an electron in a constant magnetic field. Finally, the formalism is applied to calculate the transmission probabilities through a one-dimensional delta scatterer and through a resonant tunneling structure composed of two one-dimensional quaternionic delta-scatterers in series. The results are compared to the transmission probabilities calculated using traditional (complex) quantum mechanics.

Electronic Fabry-Perot Cavity Engineered Nanoscale Thermoelectric Generators

In this work, we aim to design a heterostructure based nanoscale thermoelectric generator that can maximize the waste-heat conversion efficiency at a given output power. The primary objective to be achieved for this is to realize a boxcar-shaped (bandpass) electronic transmission function (R. S. Whitney, Phys. Rev. Lett. 112, 130601 (2014)). In order to achieve that, we propose the use of an electronic analog of optical Fabry-P\'erot cavity over a central resonant tunneling structure. We further explore the optimum design possibilities by varying the geometry of the cavity wall to ensure a nearly perfect bandpass energy filtering of electrons. Based on our findings, we propose a general design guideline to realize such transmission and demonstrate that such devices can be excellent thermoelectric generators compared to the existing proposals in terms of boosting the output power without a cost in efficiency. It is theoretically demonstrated using the non-equilibrium Green's function technique coupled with self-consistent charging effects that an enhancement in the maximum output power up to $116\%$ can be achieved through this scheme at a $10\%$ higher efficiency as compared to resonant tunneling based devices. Furthermore, an elaborate comparative study of the linear response parameters is also presented and explained in terms of the physical transport properties. This study suggests an optimal device design strategy for an improved thermoelectric generator and sets the stage for a new class of thermoelectric generators facilitated via transmission lineshape engineering.

Room-temperature Operation of Low-voltage, Non-volatile, Compound-semiconductor Memory Cells

Whilst the different forms of conventional (charge-based) memories are well suited to their individual roles in computers and other electronic devices, flaws in their properties mean that intensive research into alternative, or emerging, memories continues. In particular, the goal of simultaneously achieving the contradictory requirements of non-volatility and fast, low-voltage (low-energy) switching has proved challenging. Here, we report an oxide-free, floating-gate memory cell based on III-V semiconductor heterostructures with a junctionless channel and non-destructive read of the stored data. Non-volatile data retention of at least 104 s in combination with switching at ≤2.6 V is achieved by use of the extraordinary 2.1 eV conduction band offsets of InAs/AlSb and a triple-barrier resonant tunnelling structure. The combination of low-voltage operation and small capacitance implies intrinsic switching energy per unit area that is 100 and 1000 times smaller than dynamic random access memory and Flash respectively. The device may thus be considered as a new emerging memory with considerable potential.