Double Barrier Resonant Tunneling Diodes 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.

Large-signal dynamics of resonant-tunneling diodes

A model for analyzing dynamic large-signal characteristics of double-barrier resonant-tunneling diodes (RTDs) is presented. The model is based on the analysis of dynamical trajectories in phase space, defined by the RTD bias and electron density in the RTD quantum well. We show that an accurate dynamic model can be reformulated in an approximate way, relying only on a directly measurable DC I–V curve and on few other RTD parameters, which could be easily estimated with simple DC calculations. We further demonstrate that a simple equivalent circuit, composed of a capacitor, inductor, and two resistors (RLRC), accurately describes the large-signal admittance of RTDs. The circuit elements can be described in terms of relaxation time, geometrical RTD capacitance, and low- and high-frequency resistors. The circuit has the very same structure as that previously derived for small-signal RTD admittance, although with deviating parameters, which are now dependent on the AC-signal amplitude. We show that the large-signal RTD relaxation time can be shorter and longer than the small-signal one. In the context of RTD oscillators, a shorter RTD relaxation time allows one to get higher output power at high frequencies. The availability of an accurate, general, but rather simple, physics-based model for analyzing large-signal RTD dynamics removes one of the major hindrances to the further development of sub-THz and THz RTD oscillators.

Comparative Study of Single and Double Barrier GaAs/Al0.3Ga0.7As Based Resonant Tunneling Diodes Considering NEGF

The growth of pepped-up determining demand of final consumers always forces devices and circuits to increase power and speed. Only resonant tunneling diode can solve this problem and can be able to take a vital role in many nanoscale applications. This research paper demonstrates the simulations of the Resonant Tunneling Diode (RTD) by using Hartree Model for the single barrier (1B) and the double barrier (2B) Resonant Tunneling Diodes by the using of NEMO5 considering NEGF. In addition, switching applications also require a Large Peak to Valley Voltage Ratio (PVVR) to reduce energy loss. In this article, it has been clearly explained that compared to the Thomas Fermi Model, Hartree Model improves the Peak to Voltage Valley Ratio (PVVR) by 21.21%. The results of the Double Barrier RTD showed much better performance than the Single Barrier RTD. Furthermore, the I-V characteristic verified the notable improvement for the Hartree model.

Simulation and Comparative Study of Resonant Tunneling Diode

This paper studies and investigates the effect of physical and electrical parameters on double, triple and six barrier resonant tunneling diodes (RTD). The materials used for quantum well and barriers are Gallium arsenide (GaAs) and Aluminium gallium arsenide (AlGaAs), respectively. The parameters that were reasoned and studied include conduction band, current density, transmission coefficient and resonance energy. The above parameters were studied by changing bias voltage, temperature, barrier width and doping concentration. From the simulations performed it is observed that for double barrier RTD the peak current density is observed at 0.2 V and the valley current density is observed at 0.3 V, whereas for a triple barrier RTD the peak current density is observed at 0.015 V and the valley current density is observed at 0.06 V. The value of transmission coefficient for double barrier RTD decreases especially after bias applied is more than resonant bias (0.2 V). The effect of increasing bias leads to a decrease in the resonance level in the conduction band. The width of resonance energy decreases with the increase in barrier width. With increase in number of barrier the number of resonance level increases which leads to an increasing peaks in the transmission coefficient curve. The effect of increasing temperature leads to higher current and more resonance energy. With the thickening of barrier width, less transmission of electrons occurs leading to a reduced current density. When the barriers are increased the negative differential region (NDR) is achieved at low voltages.
 HIGHLIGHTS
 
 This paper studies and investigates the effect of physical and electrical parameters on double, triple and six barrier resonant tunneling diodes (RTD)
 The parameters include conduction band, current density, transmission coefficient, and resonance energy
 The parameters were studied by changing bias voltage, temperature, barrier width, and doping concentration
 It is observed that for double barrier RTD the peak current density is observed at 0.2 V and the valley current density is observed at 0.3 V
 For a triple barrier RTD the peak current density is observed at 0.015 V and the valley current density is observed at 0.06 V
 
 GRAPHICAL ABSTRACT

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).

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.

Electroluminescence in Unipolar-Doped In0.53Ga0.47As/AlAs Resonant-Tunneling Diodes: A Competition between Interband Tunneling and Impact Ionization

We measure and analyze the light emission from a room-temperature n-type unipolar-doped ${\mathrm{In}}_{0.53}{\mathrm{Ga}}_{0.47}\mathrm{As}/\mathrm{Al}\mathrm{As}$ double-barrier resonant-tunneling diode (RTD) that occurs just above the ${\mathrm{In}}_{0.53}{\mathrm{Ga}}_{0.47}\mathrm{As}$ band edge and peaks around 1631 nm. The emission is attributed to electron-hole recombination emission made possible by holes generated in the high-field region on the collector side of the device by interband tunneling and impact ionization, which contribute comparable hole densities, according to our analysis. Although the external quantum efficiency (EQE) in our experimental configuration is rather low (\ensuremath{\approx}2 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}5}$ at 3.0-V bias), limited by suboptimal output coupling, the internal quantum efficiency (IQE) is much higher (\ensuremath{\approx}6% at 3.0-V bias), as derived from the experimental EQE and a radiometric analysis. To check this value and better understand the transport physics, we also carry out an independent estimate of the IQE using a combined interband-tunneling impact-ionization transport model, which yields an IQE of 10% at 3.0-V bias. The satisfactory agreement of theory with experimental data suggests that a RTD designed for better hole transport and superior optical coupling could become a useful light-emitting device, while retaining the intrinsic functionality of high-speed negative differential resistance, and all without the need for resistive p-type doping.

An alternating-direction hybrid implicit-explicit finite-difference time-domain method for the Schrödinger equation

This paper proposes a novel hybrid FDTD method for solving the time-dependent Schrödinger equation, which is fundamental for modeling materials and designing nanoscale devices. The wave function is propagated on nonuniform grids by applying explicit updates in part of the grid and implicit updates elsewhere. The latter are based on the Alternating-Direction Implicit (ADI) scheme while the former are constructed with a central difference for the time derivative. A rigorous stability analysis proves that spatial steps can be selectively removed from the stability criterion thus combining the unconditional stability of the ADI scheme with fast explicit calculations. The scheme excels in its flexibility by efficiently discretizing and balancing explicit with implicit updates, as such expediting the computations. Moreover, it retains the linear complexity of explicit schemes with respect to space and time, making it especially scalable to numerically large problems. Several numerical experiments, including a laterally tunnel-coupled quantum wire and a nanowire double-barrier resonant-tunneling diode, show the validity of the scheme by demonstrating its high accuracy and decreased CPU time compared to traditional methods.

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.

Fermi Velocity Modulation Induced Low‐Bias Negative Differential Resistance in Graphene Double Barrier Resonant Tunneling diode

AbstractNegative differential resistance (NDR) devices are adequate candidates for the functional devices applicable to the next‐generation integrated circuit technology so‐called “Beyond CMOS.” Here, a graphene velocity‐modulation‐barrier resonant‐tunneling diode operating at room temperature is proposed. The current–voltage characteristics of the device are analyzed using the non‐equilibrium Green's function technique. It is found that the Fermi velocity barrier in the well/barrier region manipulates the tunneling transmission probability by suppressing the Klein region and improving the resonant tunneling leading to NDR. For special values of velocity barriers, resonant states have maximum alignment with each other which increases peak current with a high peak to valley ratio (PVR). The width and the position of the NDR window are controlled and engineered by the device dimensions and the height of potential barriers. The smaller the device showed the better the NDR properties such as larger current density and maximum PVR. Taken together, the results reveal that adequate magnitude of the Fermi velocity in graphene barrier can be an impressive concept for the fabrication of emerging tunneling devices.

Highly Efficient Resonant Tunneling Diode Terahertz Oscillator With a Split Ring Resonator

Compact resonant tunneling diode (RTD) oscillators have attracted considerable attention for terahertz generation at room temperature. Here, we propose and fabricate a novel and highly efficient RTD with a square split ring resonator (SRR). An AlAs/InGaAs double-barrier RTD is integrated into the center split gap of the SRR with a perimeter of 52 μm. Coplanar stripline antennas are integrated with the SRR to increase the radiation efficiency. The highest measured oscillation frequency is 1.22 THz with an output power of ~ 7 μW. The measured highest output power is ~ 30 μW at 0.9 THz. The experimental results are in good agreement with the simulations. This work will promote the further studies of THz metamaterials.

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.

A simple analytical model for the resonant tunneling diode based on the transmission peak and scattering effect

A new analytical model for the current–voltage characteristic of a resonant tunneling diode (RTD) is presented herein, being derived from the basic integral of the Tsu–Esaki equation. The model is physics based and developed as a function of material parameters such as the effective mass, barrier heights, and Fermi levels as well as geometrical parameters such as the barrier height and well width. The material chosen for the double-barrier RTD structure is AlGaAs/GaAs. The dependence of the peak transmission on the applied voltage and the scattering effect in the active region, which are neglected in previous models, are also taken into account. The model is implemented and validated using numerical simulations, revealing that the resulting electrical characteristic is in good agreement with numerical simulations using the Green’s function formalism.

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.

Negative differential resistance of CaF2/Si double barrier resonant tunneling diodes fabricated using plasma etching mesa isolation process

We demonstrated the negative differential resistance (NDR) characteristics in CaF2/Si double barrier resonant tunneling diodes (DBRTDs) which have mesa structure isolated by the plasma etching process using CF4/O2 plasma. Clear NDR characteristics with a peak to valley current ratio of 79 and a current density of 1–10 kA cm−2 was obtained from a CaF2/Si DBRTD mesa-isolated using CF4/O2 plasma etching at room temperature. Furthermore, any degradation of performance of the DBRTD caused by dry etching has not been observed. The NDR characteristics were reasonably reproduced by theoretical analysis based on a ballistic transport model. These results implied that the plasma etching process using CF4/O2 enables CaF2/Si heterostructure devices to be implemented into the Si-based integrated circuit technology.