Resonant Tunneling Heterostructures Research Articles

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.

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.

Comparative investigation between complex energy and transfer matrix techniques for quasi-energy states in heterostructure materials

A comparative analysis is performed to study the resonant tunneling through symmetric multiple double-barrier resonant tunneling heterostructure materials composed of nanoscale semiconductors ZnSe/BeTe, AlAs/GaAs, InGaAs/AlInAs, and AlGaAs/GaAs. Two techniques are applied in the present investigation for calculating the quasi-resonant energy states and their associated lifetimes in nanoscale double-barrier quantum well heterostructures. The first technique is based on the complex energy solution of the time-dependent Schrödinger equation with the time–energy uncertainty condition. The second one is employing the transfer matrix method. The quasi-resonant energies, lifetimes, and frequencies in nanoscale double-barrier quantum well heterostructures are calculated by both methods and compared. The validity and accuracy of both techniques are tested and compared extensively with various current numerical methods. Excellent agreements are obtained between our results and the available experimental and theoretical values. It is also found that the complex energy technique is recommended when handling the quasi-energy states and quasi-lifetimes of novel nanoscale devices.

The optimum configuration design of a nanostructured thermoelectric device with resonance tunneling

A nanostructured thermoelectric device is designed by connecting a double-barrier resonant tunneling heterostructure to two electron reservoirs. Based on Landauer’s equation and Fermi–Dirac statistics, the exact solution of the heat flow is calculated. The maximum power output and efficiency are calculated through the optimizations of several key parameters. The optimum characteristic curve of the performance is obtained. The thermodynamic performance characteristics of thermodynamic device are analyzed, including output power and efficiency, and the optimal operation region of device is determined by optimize the main parameter. The results obtained show that the heterojunction may become a perfect energy filter by appropriately regulating the chemical potentials of electron reservoirs and optimally choosing the widths of barrier and quantum well and the nanostructured thermoelectric device with resonance tunneling may obtain simultaneously a large power output and a high efficiency.

ULTRARAM: A Low‐Energy, High‐Endurance, Compound‐Semiconductor Memory on Silicon

AbstractULTRARAM is a nonvolatile memory with the potential to achieve fast, ultralow‐energy electron storage in a floating gate accessed through a triple‐barrier resonant tunneling heterostructure. Here its implementation is reported on a Si substrate; a vital step toward cost‐effective mass production. Sample growth using molecular beam epitaxy commences with deposition of an AlSb nucleation layer to seed the growth of a GaSb buffer layer, followed by the III–V memory epilayers. Fabricated single‐cell memories show clear 0/1 logic‐state contrast after ≤10 ms duration program/erase pulses of ≈2.5 V, a remarkably fast switching speed for 10 and 20 µm devices. Furthermore, the combination of low voltage and small device capacitance per unit area results in a switching energy that is orders of magnitude lower than dynamic random access memory and flash, for a given cell size. Extended testing of devices reveals retention in excess of 1000 years and degradation‐free endurance of over 107 program/erase cycles, surpassing very recent results for similar devices on GaAs substrates.

Optical Mapping of Nonequilibrium Charge Carriers

We investigate the energy relaxation segmentation in a resonant tunneling heterostructures by assessing the optical and transport dynamics of non-equilibrium charge carriers. The electrical and optical properties are analyzed using electronic transport measurements combined with electro- and photoluminescence spectroscopies in continuous-wave mode. The radiative recombination is mainly governed by the creation of heavy holes \textit{via} impact ionization processes. Our results suggest hot electrons and holes populations form independent non-equilibrium systems that do not thermalize among them and with the lattice. Consequently, the carriers effective temperature changes independently at different regions of the heterostructure, with a population distribution for holes colder than for electrons.

Strain Compensated InGaAs/AlAs Triple Barrier Resonant Tunneling Structures for THz Applications

We report a theoretical study of InGaAs/AlAs triple barrier resonant tunnelling heterostructures which are optimised for operation in the terahertz frequency range, and compare these to current state of the art double barrier structures realised in the literature. We consider the effect of strain introduced due to the large lattice mismatch of the substrate, quantum well and potential barrier materials and describe designs with strain compensated active regions. Constraints have been imposed on the designs to minimise charge accumulation in the emitter quantum well which is often associated with more complex triple barrier structures. The use of a triple barrier structure suppresses the off resonance leakage current, thus increasing the maximum output power density, with � 3 mW�m

New Tunneling Features in Polar III-Nitride Resonant Tunneling Diodes

Double barrier GaN/AlN resonant tunneling heterostructures have been grown by molecular beam epitaxy on the (0001) plane of commercially available bulk GaN substrates. Resonant tunneling diodes were fabricated; room temperature current-voltage measurements reveal the presence of a negative differential conductance region under forward bias with peak current densities of ~6.4 $kA/cm^2$ and a peak to valley current ratio of ~1.3. Reverse bias operation presents a characteristic turn-on threshold voltage intimately linked to the polarization fields present in the heterostructure. An analytic electrostatic model is developed to capture the unique features of polar-heterostructure-based resonant tunneling diodes; both the resonant and threshold voltages are derived as a function of the design parameters and polarization fields. Subsequent measurements confirm the repeatability of the negative conductance and demonstrate that III-nitride tunneling heterostructures are capable of robust resonant transport at room temperature.

Coherent Interlayer Tunneling and Negative Differential Resistance with High Current Density in Double Bilayer Graphene-WSe2 Heterostructures.

We demonstrate gate-tunable resonant tunneling and negative differential resistance between two rotationally aligned bilayer graphene sheets separated by bilayer WSe2. We observe large interlayer current densities of 2 and 2.5 μA/μm2 and peak-to-valley ratios approaching 4 and 6 at room temperature and 1.5 K, respectively, values that are comparable to epitaxially grown resonant tunneling heterostructures. An excellent agreement between theoretical calculations using a Lorentzian spectral function for the two-dimensional (2D) quasiparticle states, and the experimental data indicates that the interlayer current stems primarily from energy and in-plane momentum conserving 2D-2D tunneling, with minimal contributions from inelastic or non-momentum-conserving tunneling. We demonstrate narrow tunneling resonances with intrinsic half-widths of 4 and 6 meV at 1.5 and 300 K, respectively.

PT-symmetry breaking in resonant tunneling heterostructures

We present fermionic model based on symmetric resonant tunneling heterostructure, which demonstrates spontaneous symmetry breaking in respect to combined operations of space inversion (P) and time reversal (T). PT-symmetry breaking manifests itself in resonance coalescence (collapse of resonances). We show that resonant energies are determined by eigenvalues of auxiliary pseudo-Hermitian PT-invariant Hamiltonian.

Assessment of the resistance to diffusion destruction of AlAs/GaAs nanoscale resonant-tunneling heterostructures by IR spectral ellipsometry

A technique for assessing the quality of AlAs/GaAs nanoscale resonant-tunneling heterostructures from the viewpoint of their resistance to diffusion destruction is developed. The diffusive spreading of AlAs/GaAs heterostructure layers is revealed by infrared (IR) spectral ellipsometry and the Al and Si diffusion coefficients in GaAs are determined.

Nonlinear theory of the narrow-band generation and detection of terahertz radiation in resonant tunneling heterostructures

The nonlinear regime of high-frequency response for resonant tunneling structures in a time-periodic electric field has been investigated using a technique for solving the time-dependent Schrodinger equation based on a Floquet mode expansion of the wave functions. The dependences of current harmonic amplitudes on ac signal amplitude have been calculated and the limiting values of the generated field have been determined for singleand double-well resonant tunneling structures. The dynamic Stark effect is shown to play an important role in the formation of response. It leads to a quadratic (in ac field amplitude) shift in the positions of resonances Er in single-well structures and in double-well ones in the nonresonant case and to a splitting at resonance hν ≈ Er2–Er1 (ν is the signal frequency, Er1 and Er2 are the energies of the size-quantization levels) in double-well structures proportional to the ac signal amplitude. The phenomenon of ac signal detection by resonant tunneling structures has been investigated. The effect of resonant direct-current amplification in double-well structures has been detected at a signal frequency satisfying the condition hν ≈ Er2–Er1. In asymmetric systems, detection is shown to be possible in the absence of a dc bias, which allows zero-biased detectors based on them to be created.

A linearized model of quantum transport in the asymptotic regime of quantum wells

The effects of the local accumulation of charges in resonant tunnelling heterostructures have been described using 1D Shrodinger-Poisson Hamiltonians in the asymptotic regime of quantum wells. Taking into account the features of the underling physical system, the corresponding linearized model is naturally related to the adiabatic evolution of shape resonances on a time scale which is exponentially large w.r.t. the asymptotic parameter h. A possible strategy to investigate this problem consists of using a complex dilation to identify the resonances with the eigenvalues of a deformed operator. Then, the adiabatic evolution problem for a sheet-density of charges can be reformulated using the deformed dynamical system which, under suitable initial conditions, is expected to evolve following the instantaneous resonant states. After recalling the main technical difficulties related to this approach, we introduce a modified model where h-dependent artificial interface conditions, occurring at the boundary of the interaction region, allow one to obtain adiabatic approximations for the relevant resonant states, while producing a small perturbation of the dynamics on the scale h0 . According to these results, we finally suggest an alternative formulation of the adiabatic problem. An a posteriori justification of our method is obtained by considering an explicitlysolvable case.

Quality diagnostics of nanoscale AlAs/GaAs resonant tunnelling heterostructures based on IR-spectroscopic ellipsometry

In this work, the procedure of assessing the quality of AlAs/GaAs resonant tunnelling heterostructures with relation to their resistance to diffusion destruction was developed. The diffusion blur of the AlAs/GaAs heterostructure layers was detected by means of infrared-spectroscopic ellipsometry. The diffusion coefficients of Al and Si in GaAs were also calculated.

Tunneling through a GaN/AlN-based double-barrier resonant tunneling heterostructure

The results of the fabrication and study of a double-barrier resonant tunneling structure grown on the basis of GaN and AlN wide-gap materials on a (0001)-oriented sapphire substrate are given. It is shown that, at voltages of ∼3 V, the current-voltage characteristics of resonant tunneling diode samples exhibit a region of negative differential conductivity that disappears upon multiple cyclic measurements. It is also shown that the reversal of sign of the applied voltage restores the initial shape of the current-voltage characteristics and an increase in the temperature of the structure from room temperature to 200°C yields irreversible degradation of the device and a shift of the region of negative differential conductivity to lower voltages

Конструкторско-технологическое проектирование микроэлектронных нелинейных преобразователей СВЧ радиосигналов на основе многослойных полупроводниковых наноразмерных резонансно-туннельных гетероструктур

Конструкторско-технологическое проектирование микроэлектронных нелинейных преобразователей СВЧ радиосигналов на основе многослойных полупроводниковых наноразмерных резонансно-туннельных гетероструктур

Modeling of peak voltage and current of nanowire resonant tunneling devices: case study on InAs/InP double-barrier heterostructures

SUMMARY In this paper, we develop an analytical model for the prediction of the peak voltage and the current in the current–voltage characteristics of nanowire resonant tunneling heterostructures. The model is applied in the case study of double-barrier InAs/InP devices, and the results are obtained from numerical carrier transport calculations, in terms of structural parameters such as the nanowire radius as well as the width of the barriers and quantum well. Copyright © 2013 John Wiley & Sons, Ltd.

Detection of single photons by a resonant tunneling heterostructure with a quantum dot layer

Light absorption by GaAs/AlAs heterostructures with a layer of self-assembled InAs quantum dots (QDs) at resonant tunneling through an energy-selected QD has been investigated. A high sensitivity of the current through this selected tunneling channel to the absorption of single photons with a wavelength λ ≲ 860 nm up to a temperature of 50 K is demonstrated; this sensitivity is caused by the Coulomb effect of the photoexcited holes captured by surrounding QDs on the resonance conditions. It is shown that single-photon absorption can discretely change the current through the system under study by a factor of more than 50. The captured-hole lifetimes have been measured, and a model has been developed to qualitatively describe the experimental data. It is also demonstrated that the InAs monolayer can effectively absorb photons. The properties of the heterostructure studied can be used not only to detect photons but also to design logical valves and optical memory devices.

Integration of GaAs/In0.1Ga0.9As/AlAs resonance tunneling heterostructures into micro‐electro‐mechanical systems for sensor applications

AbstractDouble‐barrier quantum‐well resonant tunneling heterostructures of GaAs/In0.1Ga0.9As/AlAs have been used as pressure‐sensing elements of designed micro‐electro‐mechanical systems. The static experiments have been conducted on the heterostructure, in both positive and negative differential resistance (PDR and NDR) regions, showing a piezoresistive coefficient of 3.85 × 10−9 Pa−1, which is about seven times larger than that of piezoresistive silicon devices. At the same time, the devices also provided an improved dynamic response (119.6 µV · g−1 V−1) and signal‐to‐noise ratio (57 dB) in the NDR region.

Spin-polarization in InAs/AlSb double barrier resonant tunneling structures: influence of barrier material and interface structure

We present a study on the atomistic simulation of the spin-polarized transmissions through InAs/AlSb double barrier resonant tunneling heterostructures. By making use of the atomistic sp3s* tight binding Hamiltonian including the intra-atomic spin-orbit interaction and the recursive Green’s function method, we obtain the significant anisotropic zero-magnetic-field spinsplitting of the resonant transmission peak in the absence of the external electric field, demonstrating the importance of the barrier material and the atomic scale detail of the hetero interfaces on the spin-splitting.