Double Barrier Resonant Tunneling Research Articles

Resonant Tunnelling and Intersubband Optical Properties of ZnO/ZnMgO Semiconductor Heterostructures: Impact of Doping and Layer Structure Variation.

ZnO-based heterostructures are up-and-coming candidates for terahertz (THz) optoelectronic devices, largely owing to their innate material attributes. The significant ZnO LO-phonon energy plays a pivotal role in mitigating thermally induced LO-phonon scattering, potentially significantly elevating the temperature performance of quantum cascade lasers (QCLs). In this work, we calculate the electronic structure and absorption of ZnO/ZnMgO multiple semiconductor quantum wells (MQWs) and the current density-voltage characteristics of nonpolar m-plane ZnO/ZnMgO double-barrier resonant tunnelling diodes (RTDs). Both MQWs and RTDs are considered here as two building blocks of a QCL. We show how the doping, Mg percentage and layer thickness affect the absorption of MQWs at room temperature. We confirm that in the high doping concentrations regime, a full quantum treatment that includes the depolarisation shift effect must be considered, as it shifts mid-infrared absorption peak energy for several tens of meV. Furthermore, we also focus on the performance of RTDs for various parameter changes and conclude that, to maximise the peak-to-valley ratio (PVR), the optimal doping density of the analysed ZnO/Zn88Mg12O double-barrier RTD should be approximately 1018 cm-3, whilst the optimal barrier thickness should be 1.3 nm, with a Mg mole fraction of ~9%.

Record peak current density of over 1500 kA/cm2 in highly scaled AlN/GaN double-barrier resonant tunneling diodes on free-standing GaN substrates

This work demonstrates high-performance AlN/GaN double-barrier resonant tunneling diodes (RTDs) with high peak current density grown by plasma-assisted molecular beam epitaxy on c-plane free-standing GaN substrates, featuring stable and repeatable negative differential resistance (NDR) characteristics at room temperature. By scaling down the barrier thickness of AlN barrier and the lateral mesa size of collector, the record peak current density of 1551 kA/cm2 is achieved along with a peak-to-valley current ratio (PVCR) of 1.24, which is attributed to the reduced resonant tunneling time under thinner AlN barrier and the suppressed external incoherent valley current by reducing the dislocation number contained in the RTD device with the smaller size of collector. By statistically analyzing the NDR performance of RTD devices with different thicknesses of AlN barrier, the average peak current density increases from 145.7 to 1215.1 kA/cm2, while the average PVCR decreases from 1.45 to 1.1, correspondingly, accompanying with a decreased peak voltage from 6.89 to 5.49 V, with downscaling the AlN barrier thickness from 1.5 to 1.25 nm. The peak current density obtained in this work is the highest value among all the reported nitride-based RTDs up until now while maintaining high PVCR value simultaneously, which illustrates that ultra-scaled RTD based on vertical quantum-well structure and lateral collector size is a valuable approach for the development of nitride-based RTDs with excellent NDR characteristics and reveals their great potential applications in high-frequency oscillation sources and high-speed switch circuits.

Opto-electronic transport properties of resonant tunneling diodes with type-I and II postwells

We investigate the opto-electronic transport properties of AlGaAs/GaAs double-barrier resonant tunneling diodes (RTDs) with GaAs1−xSbx type-II postwells and compare these to RTDs with InxGa1−xAs type-I postwells. Samples grown with Sb containing type-II postwells show a significant photocurrent enhancement for x = 24% compared to 5.5% and 34%, respectively, which is attributed to an efficient hole trapping based on the large hole trapping barrier of 396 meV. By contrasting the RTDs with type-I InGaAs quantum well RTDs, we observe an increased photoresponsivity by one order of magnitude. Our finding allows realizing RTD with efficient hole trapping in the vicinity of the active region of the double barrier structure with confinement energies well above the thermal energy at room temperature, which may allow the observation of single charge configurations even at elevated temperatures.

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.

Study of Electronic and Transport Properties in Double-Barrier Resonant Tunneling Systems.

Resonant tunneling devices are still under study today due to their multiple applications in optoelectronics or logic circuits. In this work, we review an out-of-equilibrium GaAs/AlGaAs double-barrier resonant tunneling diode system, including the effect of donor density and external potentials in a self-consistent way. The calculation method uses the finite-element approach and the Landauer formalism. Quasi-stationary states, transmission probability, current density, cut-off frequency, and conductance are discussed considering variations in the donor density and the width of the central well. For all arrangements, the appearance of negative differential resistance (NDR) is evident, which is a fundamental characteristic of practical applications in devices. Finally, a comparison of the simulation with an experimental double-barrier system based on InGaAs with AlAs barriers reported in the literature has been obtained, evidencing the position and magnitude of the resonance peak in the current correctly.

Statistical device simulations of III-V nanowire resonant tunneling diodes as physical unclonable functions source

In this paper, utilising the non-equilibrium Green’s function (NEGF) formalism within the new device simulator NESS (Nano-Electronic Software Simulator) developed at the University of Glasgow’s Device Modelling Group, we present quantum mechanical simulations of current flow in double-barrier III-V GaAs-AlGaAs nanowire resonant tunneling diodes (RTDs). NESS is a fast and modular Technology Computer Aided Design (TCAD) tool with flexible architecture which can take into account various sources of statistical variability in nanodevices. The aim of this work is to show that, in the RTD devices with nano-scale dimensions, there is a direct correlation between the position and the numbers of random dopants and the key device parameters, e.g., position of the resonant-peak (VR) variations as well as the shape and number of peaks in the output current–voltage (I-V) characteristics. Such VR variability can be used as a quantum fingerprint which can provide robust security and hence can be used to deliver Physical Unclonable Functions (PUFs).

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.

Analytical Modeling and Band-Structure Engineering of Resonant Tunneling Diode for Biased Terahertz Detector

A new strategy to significantly enhance the nonlinearity of double-barrier resonant tunneling diode (RTD) in the positive differential resistance region is theoretically proposed and experimentally demonstrated. An analytical model containing physical insight into the resonant tunneling process is established to bridge the nonlinearity of the current–voltage curve and the band-structure information of RTD. It intuitively shows that the intrinsic current responsivity of RTD as well as its nonlinearity can be greatly improved via band-structure engineering, as enhancing the resonant energy level of the well and reducing the current before the resonant tunneling process. The validation of the proposed model and the associated band-structure engineering strategy are verified by both device simulation and experiments. A RTD device with intrinsic current responsivity of 6.74 A/W is realized, while the peak-to-valley current ratio (PVCR) is also as large as 8.92. This method provides a new pathway to design high-performance terahertz (THz) detectors using double-barrier RTD and may share new perspective on the potential of RTD-based THz transceivers.

1039 kA/cm2 peak tunneling current density in GaN-based resonant tunneling diode with a peak-to-valley current ratio of 1.23 at room temperature on sapphire substrate

In this Letter, we present the excellent negative differential resistance (NDR) characteristics of AlN/GaN double-barrier resonant tunneling diodes (RTDs) in which the active layers are grown by molecular beam epitaxy on thick GaN-on-sapphire templates manufactured by metal-organic chemical vapor deposition. Here, indium flux is introduced as surfactant to reduce the interface roughness and improve the sharpness of heterointerface during epitaxial growth of AlN/GaN/AlN quantum well. The processed device with a top collector diameter of 1 μm size demonstrates a record peak current density of 1039 kA/cm2 while simultaneously featuring a peak-to-valley current ratio of 1.23 at room temperature, excellent achievements among all the reported GaN-based RTDs on any substrates. In addition, no degradation of device performance together with free of hysteresis is observed for the 1000 times consecutive up-to-down voltage sweeps under forward bias. These remarkable achievements are attributed to the marked improvement in heterointerface quality of AlN/GaN/AlN double-barrier quantum well by adopting indium as surfactant during epitaxial growth as clarified by transmission electron microscopy analysis, which dramatically suppresses the interface roughness scattering and elements interdiffusion, thus significantly improving the NDR signatures in current–voltage curves. The obtained results in this work illustrate that indium-surfactant added epitaxy technique turns out to be a promising approach for the modulation of vertical electron resonant tunneling in III-nitride heterostructures and realization of highly reproducible and reliable AlN/GaN double-barrier RTDs, in favor of implementation for future high-power solid-state electronics operating in terahertz spectra.

Demonstration of highly repeatable room temperature negative differential resistance in large area AlN/GaN double-barrier resonant tunneling diodes

Here, we present a systematical investigation of AlN/GaN double-barrier resonant tunneling diodes (RTDs) grown by plasma-assisted molecular beam epitaxy on metal-organic chemical vapor deposition GaN-on-sapphire templates. The processed devices featured an active region composed of 2.5 nm GaN quantum well sandwiched by two 1.5 nm AlN barriers and RTD mesa diameter ranging from 1 to 20 μm. Room temperature current–voltage characteristics exhibited a repeatable negative differential resistance (NDR) free of degradation and hysteresis after 1000 times subsequently up-to-down voltage sweeps across different sizes. High peak-to-valley current ratios of 1.93 and 1.58 were obtained at room temperature for 1 and 12 μm diameter devices, respectively, along with peak current densities of 48 and 36 kA/cm2 corresponding to peak voltages of 4.65 and 5.9 V. The peak current density decreased quickly initially and then was less susceptible to this averaging effect with increasing the device diameter. Temperature-dependent measurements revealed that the valley current density displayed a positive relationship to the temperature, and an abruptly increasement was observed for the devices with a diameter of 20 μm when the temperature rose over 230 K. We attributed this abnormal phenomenon to the increased contribution from acoustic and longitudinal optical (LO) phonon scattering, especially for the LO phonon scattering. The area dependence of electrical performance suggested that the leakage pathway through dislocations played a vital role for charge transport and there existed a threshold of dislocation density for NDR characteristics. These results promote further study for future implementation of III-nitride-based RTD oscillators into high-frequency and high-power terahertz radiation.

Pulsed terahertz radiation from a double-barrier resonant tunneling diode biased into self-oscillation regime

The study of the bolometer response to terahertz (THz) radiation from a double-barrier resonant tunneling diode (RTD) biased into the negative differential conductivity region of the I–V characteristic revealed that the RTD emits two pulses in a period of intrinsic self-oscillations of current. The bolometer pulse repetition rate is a multiple of the fundamental frequency of the intrinsic self-oscillations of current. The bolometer pulses are detected at two critical points with a distance between them being half or one-third of a period of the current self-oscillations. An analysis of the current self-oscillations and the bolometer response has shown that the THz photon emission is excited when the tunneling electrons are trapped in (the first pulse) and then released from (the second pulse) miniband states.

Enhanced negative differential resistance in silicene double-barrier resonant tunneling diodes

We investigate the transport properties of double-barrier resonant tunneling diodes based on silicene nanoribbons by means of transfer matrix method under the external electric field. It is found that the transmission shows resonance suppression (enhancement) under the positive (negative) bias. The spin-dependent and valley-dependent negative differential resistance (NDR) characteristics are found both in the symmetric and asymmetric structures. The influence of various factors on the I-V characteristics is analyzed, it is found that the NDR characteristics can be greatly enhanced by the structural parameters, Fermi energy, and band gap. What should be laid stress on is that the maximum peak-to-valley ratio (PVR) can reach up to 13 by regulating the band gap. Proposed structure here could be the base of other high-frequency electronics devices.

Dependence of growth temperature on the electrical properties and microstructure of MBE-grown AlN/GaN resonant tunneling diodes on sapphire

AlN/GaN double-barrier resonant tunnel diodes have been grown by rf-plasma assisted molecular beam epitaxy at temperatures between 760 and 860 °C on metalorganic chemical vapor deposition-grown GaN templates with sapphire substrates. Room temperature negative differential resistance (NDR) was observed for all samples despite the presence of higher densities of threading dislocations in the device layers than in the MOCVD GaN template. The fraction of devices exhibiting NDR and the peak-to-valley current ratio was small for each sample (typically 1%–10% and 1.003–1.1, respectively). A clear trend of increasing peak current density with increasing growth temperature was observed.

Investigation of Switching Time in GaN/AlN Resonant Tunneling Diodes by Experiments and P-SPICE Models

The experimental and simulated switching behavior across the negative differential resistance (NDR) region of GaN/AlN double-barrier resonant tunneling diodes (RTDs) is presented. The shortest 10%–90% experimental switching time was ~55 ps. The experimental results are also studied with P-SPICE circuit models, which show that the relatively low peak-to-valley current ratio (~1.5), relatively high specific contact resistance ( $\geq \textsf {1}\times \textsf {10}^{-\textsf {6}}\,\,\Omega $ -cm2), and relatively large specific capacitance limit the switching time.

Time-Dependent Resonant Tunneling in a Double-Barrier Diode Structure

A new model of time-dependent tunneling without the introduction of boundary conditions has been proposed to describe the joint solution of the time-dependent Schrodinger and Poisson equations. The model is based on an integral equation obtained by the time-dependent Green’s function method. This function implements the spatial nonlocality of a wavepacket, but it is sufficient to seek a solution in a finite region. The consideration has been performed for a double-barrier resonant tunneling diode.

Electronic Transport and Resonant Tunneling Properties of Hyperbolic Pöschl-Teller Double-Barrier Structures

The ballistic electron transport characteristics of hyperbolic Pöschl-Teller double-barrier resonant tunneling structures are investigated. The transmission coefficient and the current density-voltage characteristic in electrically biased one dimensional hyperbolic Pöschl-Teller double-barrier structures with different structure parameters have been calculated by using non-equilibrium Green’s function method. Results for the transmission coefficients and the current densities are compared with the barrier shapes. The results show that the widths of the wells and heights of barriers have a significant effect on the transmission properties. The current density-voltage characteristic presents N-type negative differential resistance.

Quantum resonant tunneling in semiconductor double-barrier structure

Using Schrodinger equation, we have theoretically studied the quantum transport in double-barrier potential resonant tunneling diodes. To obtain higher peak in transmission coefficient in twofold barrier quantum well system require to reducing the barrier height and increasing the width of the quantum well which causes the electrons to turn unbounded. In addition, the potential energies should be below the height of the barrier. This occurs because on resonance with unity transmission requires exact cancellation in amplitude and phase of a coherent superposition of all contributions to the back-scattered particle-waves. At a certain height, width and potential energy, the resonances sit-down between barriers giving rise to peaks in transmission. Our model can be extended for several barriers to increasing the resonance peaks of transmission.

Bandgap engineered graphene and hexagonal boron nitride for resonant tunnelling diode

In this article a double-barrier resonant tunnelling diode (DBRTD) has been modelled by taking advantage of single-layer hexagonal lattice of graphene and hexagonal boron nitride (h-BN). The DBRTD performance and operation are explored by means of a self-consistent solution inside the non-equilibrium Green’s function formalism on an effective mass-Hamiltonian. Both p- and n-type DBRTDs exhibit a negative differential resistance effect, which entails the resonant tunnelling through the hole and electron bound states in the graphene quantum well, respectively. The peak-to-valley ratio of approximately 8 (3) for p-type (n-type) DBRTD with quantum well of 5.1 nm (4.3 nm) at a barrier width of 1.3 nm was achieved for zero bandgap graphene at room temperature.

A New Proposal for Simultaneous Multicolor Detection Based on Quantum Dots and Selective Energy Contacts

In this paper, simultaneous multiwavelength detection using quantum dots (QDs) and energy selective contacts is investigated. This detection can be achieved by intersubband and interband transitions in QD-based superlattices. Here, we show that attaching a double-barrier resonant tunneling to the QD-based active layer solves the basic problem of carrier extraction from each discrete energy level to individual electrodes (as a multicontact package). The mini-band energy levels and corresponding wave functions for arrays of QDs are calculated using the 2-D Schrodinger equation. We present simultaneous multiwavelength detection by QD structures with selective contacts for the first time according to the best of our knowledge. This paper opens the way to new strategies in the engineering and the fabrication of simple detectors for multiband radiation detection. In addition, for more clarification, photocurrent and dark current of photodetector with two independent output paths are obtained.

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