Resonant Tunneling Research Articles

Design of Molecular Positive Electronic Transition Device

This work presents an investigation on the electronic transport of two devices based on Zigzag Phagraphene Nanoribbons of different widths (ZPGNR1 and ZPGNR2) with Nitrogen-doped edge terminations based on DFT-NEGF methodology using TranSIESTA code. Our results show different transport regimes: (i) ZPGNR1 device exhibits metallic behavior and metal-semiconductor transition when the bias voltage is increased, with symmetry on the eigenchannels (ECs) and the field-effect transistor (FET) signature; and (ii) ZPGNR2 device presents topological insulator (TI) behavior and two operation windows, the first with FET signature characterized by the TI-semiconductor transition and the second with resonant tunnel diode (RTD) signature with broken ECs symmetry due to potential barrier caused by N-doping at the edge and the central region is preferential transport path for the device, inherent to TI systems, generating a negative differential resistance (NDR). Another alternative for ZPGNR2 is to consider a current limiter device Molecular Positive Electronic Transition (MPET)-like.

반도체 전자소자 기반 테라헤르츠 신호원

Terahertz (THz) signal sources are important elements that are used in THz systems and have been gaining interest in recent times. THz signal sources can be realized using either optical devices or electronic devices. The latter approach can be divided into signal sources based on vacuum devices and solid-state devices. This paper provides an overview of THz sources that use semiconductor electronic devices, which are a typical kind of the solid-state devices. First, the operational principles and recent performance trends of diode-based THz signal sources, such as Gunn diodes, impact ionization avalanche transit-time (IMPATT) diodes, and resonant tunneling diodes (RTDs), are provided. Next, three types of transistor circuit-based THz signal sources, namely, LC cross-coupled oscillators, Colpitts oscillators, and ring oscillators, are described according to their topologies and performance. Finally, various types of 300 GHz and 600 GHz oscillators are introduced as representative examples of transistor circuit-based signal sources.

Position-dependent mass effects on a bilayer graphene catenoid bridge

We study the electronic properties of a position-dependent effective mass electron on a bilayer graphene catenoid bridge. We propose a position-dependent mass (PDM) as a function of both gaussian and mean curvature. The hamiltonian exhibits parity and time-reversal steaming from the bridge symmetry. The effective potential contains the da Costa, centrifugal and PDM terms which are concentrated around the catenoid bridge. For zero angular momentum states, the PDM term provides a transition between a reflectionless to a double-well potential. As a result, the bound states undergo a transition from a single state around the bridge throat into two states each one located at rings around the bridge. Above some critical value of the PDM coupling constant, the degeneracy is restored due to double-well tunneling resonance.

Single and triple insulator Metal-Insulator-Metal diodes for infrared rectennas

Tunnel-barrier rectifiers comprising single and triple insulator configurations have been fabricated by atomic layer deposition (ALD) to investigate the insulator (Al2O3, Ta2O5, Nb2O5) layer quality and rectification performance for inclusion in rectenna arrays for infrared energy harvesting. ALD has provided superior control of nanometer film thickness (1–3 nm) as well as insulator film quality as tunneling has been found to be the dominant conduction mechanism for all fabricated devices. The key rectifier properties, such as asymmetry, non-linearity, responsivity and dynamic resistance have been assessed from current-voltage (I-V) measurements. The Au/Al2O3/Ti diode exhibits zero bias responsivity of −0.6 A/W, showing that it can be used for energy harvesting applications without the aid of external bias. The effect of resonant tunneling on rectification performance of triple insulator non-cascaded (Ta2O5/Nb2O5/Al2O3) and cascaded (Nb2O5/Ta2O5/Al2O3) rectifiers has been observed from experimental I-V characteristics and substantiated by theoretical simulations. Superior low-voltage asymmetry (6 at 0.1 V) and responsivity (4.3 A/W at 0.35 V) for triple insulator MI3M rectifiers have been observed. The resonant tunneling does not provide enhanced rectification at low bias as previously reported, rather it has much smaller effect. The latter indicates that dissimilar metal electrodes rectifier configurations are more promising for inclusion in optical rectenna.

Spin-Selective Resonant Tunneling Induced by Rashba Spin-Orbit Interaction in Semiconductor Nanowire

We consider a single electron confined within a quantum wire in a system of two electrostatically-induced QDs defined by nearby gates. The time-varying electric field, of single GHz frequency, perpendicular to the quantum wire, is used to induce the Rashba coupling and enable spin-dependent resonant tunneling of the electron between two adjacent potential wells with fidelity over 99.5%. This effect can be used for the high fidelity all-electrical electron-spin initialization or readout in the spin-based quantum computer. In contrast to other spin initialization methods, our technique can be performed adiabatically without increase in the energy of the electron. Our simulations are supported by a realistic self-consistent time-dependent Poisson-Schroedinger calculations.

Comparison of resonant tunneling diodes grown on freestanding GaN substrates and sapphire substrates by plasma-assisted molecular-beam epitaxy* *Project supported by the National Key R&D Program of China (Grant No. 2018YFB0406600), the National Natural Science Foundation of China (Grant Nos. 61875224, 61804163, and 61827823), Key Laboratory of Microelectronic Devices and Integration Technology, Chinese Academy of Sciences (Grant No. Y9TAQ21), Key Laboratory

AlN/GaN resonant tunneling diodes (RTDs) were grown separately on freestanding GaN (FS-GaN) substrates and sapphire substrates by plasma-assisted molecular-beam epitaxy (PA-MBE). Room temperature negative differential resistance (NDR) was obtained under forward bias for the RTDs grown on FS-GaN substrates, with the peak current densities (J p) of 175–700 kA/cm2 and peak-to-valley current ratios (PVCRs) of 1.01–1.21. Two resonant peaks were also observed for some RTDs at room temperature. The effects of two types of substrates on epitaxy quality and device performance of GaN-based RTDs were firstly investigated systematically, showing that lower dislocation densities, flatter surface morphology, and steeper heterogeneous interfaces were the key factors to achieving NDR for RTDs.

Highly-efficient electrically-driven localized surface plasmon source enabled by resonant inelastic electron tunneling

On-chip plasmonic circuitry offers a promising route to meet the ever-increasing requirement for device density and data bandwidth in information processing. As the key building block, electrically-driven nanoscale plasmonic sources such as nanoLEDs, nanolasers, and nanojunctions have attracted intense interest in recent years. Among them, surface plasmon (SP) sources based on inelastic electron tunneling (IET) have been demonstrated as an appealing candidate owing to the ultrafast quantum-mechanical tunneling response and great tunability. However, the major barrier to the demonstrated IET-based SP sources is their low SP excitation efficiency due to the fact that elastic tunneling of electrons is much more efficient than inelastic tunneling. Here, we remove this barrier by introducing resonant inelastic electron tunneling (RIET)—follow a recent theoretical proposal—at the visible/near-infrared (NIR) frequencies and demonstrate highly-efficient electrically-driven SP sources. In our system, RIET is supported by a TiN/Al2O3 metallic quantum well (MQW) heterostructure, while monocrystalline silver nanorods (AgNRs) were used for the SP generation (localized surface plasmons (LSPs)). In principle, this RIET approach can push the external quantum efficiency (EQE) close to unity, opening up a new era of SP sources for not only high-performance plasmonic circuitry, but also advanced optical sensing applications.

Temperature effects of GaAs/Al0.45Ga0.55As superlattices on chaotic oscillation* *Project supported by the Key Program of the National Natural Science Foundation of China (Grant No. 61834004).

For widespectrum chaotic oscillation, superlattice cryptography is an autonomous controllable brand-new technology. Originating from sequential resonance tunneling of electrons, the chaotic oscillation is susceptible to temperature change, which determines the performance of superlattices. In this paper, the temperature effects of chaotic oscillations are investigated by analyzing the randomness of a sequence at different temperatures and explained with superlattice microstates. The results show that the bias voltage at different temperatures makes spontaneous chaotic oscillations vary. With the temperature of superlattices changing, the sequence dives in entropy value and randomness at specific bias. This work fills the gap in the study of temperature stability and promotes superlattice cryptography for practice.

Gate-Tunable Negative Differential Resistance Behaviors in a hBN-Encapsulated BP-MoS2 Heterojunction.

Two-dimensional (2D) heterostructures show great potential in achieving negative differential resistance (NDR) effects by Esaki diodes and or resonant tunneling diodes. However, most of the reported Esaki diode-based NDR devices realized by bulk 2D films lack sufficient gate tunability, and the tuning of NDR behavior from appearing to vanishing remains elusive. Here, a gate-tunable NDR device is reported based on a vertically stacked black phosphorus (BP) and molybdenum disulfide (MoS2) thin 2D heterojunction. At room temperature, a rectifying ratio of ∼6 orders of magnitude from a reverse rectifying diode to a forward rectifying diode by gate modulation is obtained. Through analyzing the temperature-dependent electrical properties, the tunneling mechanism at a certain gate voltage range is revealed. Moreover, the switchable and continuously gate-tunable NDR behavior is realized with a maximum peak-to-valley ratio of 1.23 at 77 K, as shown in the IDS mappings by sweeping VDS under different VGS. In addition, a compact model for gate-tunable NDR behavior in 2D heterostructures is proposed. To our best knowledge, this is the first demonstration of NDR behavior in BP-MoS2 heterostructures. Consequently, this work sheds light on the gate-tunable NDR devices and reconfigurable logic devices for realizing ternary and reconfigurable logic systems.

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 resonant tunneling effects in metal-double-insulator-metal (MI2M) diodes

Although the effect of resonant tunneling in metal-double-insulator-metal (MI2M) diodes has been predicted for over two decades, no experimental demonstrations have been reported at the low voltages needed for energy harvesting rectenna applications. Using quantum-well engineering, we demonstrate the effects of resonant tunneling in a Ni/NiO/Al2O3/Cr/Au MI2M structures and achieve the usually mutually exclusive desired characteristics of low resistance ({R}_{0}^{DC} sim 13 kΩ for 0.035 μm2) and high responsivity (β0 = 0.5 A W−1) simultaneously. By varying the thickness of insulators to modify the depth and width of the MI2M quantum well, we show that resonant quasi-bound states can be reached at near zero-bias, where diodes self-bias when driven by antennas illuminated at 30 THz. We present an improvement in energy conversion efficiency by more than a factor of 100 over the current state-of-the-art, offering the possibility of engineering efficient energy harvesting rectennas.

48‐Gbit/s 8K video‐transmission using resonant tunnelling diodes in 300‐GHz band

The authors report on a real-time 48-Gbit/s terahertz band wireless communication experiment employing a pair of resonant tunnelling diodes at the receiver and uni-travelling carrier photodiodes at the transmitter. The wireless transmission of uncompressed full-resolution 8K ultra high-definition television video signal is successfully demonstrated in the 300-GHz band for the first time.

Doping Profile Engineered Triple Heterojunction TFETs With 12-nm Body Thickness

Triple heterojunction (THJ) TFETs have been proposed to resolve the low ON-current challenge of TFETs. However, the design space for THJ-TFETs is limited by fabrication challenges with respect to device dimensions and material interfaces. This work shows that the original THJ-TFET design with 12 nm body thickness has poor performance, because its sub-threshold swing is 50 mV/dec and the ON-current is only 6 $\mu A/\mu m$. To improve the performance, the doping profile of THJ-TFET is engineered to boost the resonant tunneling efficiency. The proposed THJ-TFET design shows a sub-threshold swing of 40 mV/dec over four orders of drain current and an ON-current of 325 uA/um with VGS = 0.3 V. Since THJ-TFETs have multiple quantum wells and material interfaces in the tunneling junction, quantum transport simulations in such devices are complicated. State-of-the-art mode-space quantum transport simulation, including the effect of thermalization and scattering, is employed in this work to optimize THJ-TFET design.

Hot electron photoemission in metal–semiconductor structures aided by resonance tunneling

Enhancement of the surface photoemission from metal into semiconductor by resonance tunneling of photoexcited electrons through (quasi-) discrete level in quantum well, located within Schottky barrier of the metal–semiconductor interface, is studied theoretically taking into account the difference between the electron masses in metal and semiconductor. It is shown, in particular, that resonance tunneling through the discrete level can lead to the redshift of the threshold wavelength of surface photoeffect, higher slope linear growth in photocurrent near the threshold (in contrast to quadratic growth, i.e., Fowler's law), and the possibility to increase substantially the photoemission efficiency similarly to recent experimental results on hot carrier generation in plasmonic structures with a discrete energy level at metal interface. The difference in the effective masses is shown to significantly affect the results. Double-barrier tunneling structures with resonant tunneling may become attractive for applications in photochemistry and in plasmonic photodetectors in near IR and middle IR regions of the spectrum.

Twisted monolayer and bilayer graphene for vertical tunneling transistors

We prepare twist-controlled resonant tunneling transistors consisting of monolayer and Bernal bilayer graphene electrodes separated by a thin layer of hexagonal boron nitride. The resonant conditions are achieved by closely aligning the crystallographic orientation of graphene electrodes, which leads to momentum conservation for tunneling electrons at certain bias voltages. Under such conditions, negative differential conductance can be achieved. Application of in-plane magnetic field leads to electrons acquiring additional momentum during the tunneling process, which allows control over the resonant conditions.

Efficiency at maximum power of thermoelectric heat engines with the symmetric semiconductor superlattice

Efficiency at maximum power (EMP) is a very important specification for a heat engine to evaluate the capacity of outputting adequate power with high efficiency. It has been proved theoretically that the limit EMP of thermoelectric heat engine can be achieved with the hypothetical boxcar-shaped electron transmission, which is realized here by the resonant tunneling in the one-dimensional symmetric InP/InSe superlattice. It is found with the transfer matrix method that a symmetric mode is robust that regardless of the periodicity, and the obtained boxcar-like electron transmission stems from the strong coupling between symmetric mode and Fabry-P\'erot modes inside the allowed band. High uniformity of the boxcar-like transmission and the sharp drop of the transmission edge are both beneficial to the maximum power and the EMP, which are optimized by the bias voltage and the thicknesses of barrier and well. The maximum power and EMP are extracted with the help of machine learning technique, and more than 95% of their theoretical limits can both be achieved for smaller temperature difference, smaller barrier width and larger well width. We hope the obtain results could provide some basic guidance for the future designs of high EMP thermoelectric heat engines.

ULTRARAM: Toward the Development of a III–V Semiconductor, Nonvolatile, Random Access Memory

ULTRARAM is a III-V compound semiconductor memory concept that exploits quantum resonant tunneling to achieve nonvolatility at extremely low switching energy per unit area. Prototype devices are fabricated in a 2×2 memory array formation on GaAs substrates. The devices show 0/1 state contrast from program/erase (P/E) cycles with 2.5 V pulses of 500- μs duration, a remarkable switching speed for a 20 μm gate length. Memory retention is tested for 8×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> s, whereby the 0/1 states show adequate contrast throughout, whilst performing 8×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> readout operations. Further reliability is demonstrated via program-read-erase-read endurance cycling for $10^{6}$ cycles with 0/1 contrast. A half-voltage array architecture proposed in our previous work is experimentally realized, with an outstandingly small disturb rate over 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> half-voltage cycles.

ДОСЛІДЖЕННЯ СЕНСОРА ТЕМПЕРАТУРИ З ЧАСТОТНИМ ВИХОДОМ НА ОСНОВІ КВАНТОВОЇ ГЕТЕРОСТРУКТУРИ З ВІД’ЄМНИМ ДИФЕРЕНЦІЙНИМ ОПОРОМ

Physical processes in a quantum two-barrier heterostructure, which is the basis for the development of tunnel-resonant diodes, are considered. These studies have shown that tunnel resonance diodes can be used as temperature sensors with a frequency output signal. The use of devices with negative differential resistance makes it possible to significantly simplify the design of temperature sensors in the entire radio frequency range, at which, depending on the operating modes of the sensor, an output signal can be obtained both in the form of harmonic oscillations and in the form of impulse oscillations of a special form. The study of the characteristics of the sensor is based on the equivalent circuit of the tunnel-resonant diode, which takes into account its capacitive and inductive properties. The current-voltage characteristic of the sensor has a falling section, which is responsible for the appearance of a negative differential resistance in this section. The descending section arises due to a decrease in the current that flows through the double-barrier quantum heterostructure, with an increase in voltage. A decrease in the current occurs due to a decrease in the transparency coefficient of the potential barriers of the heterostructure. A mathematical model of the temperature sensor has been developed, on the basis of which the analytical dependences of the change in the elements of the equivalent circuit of the sensor on temperature, as well as the transformation function and sensitivity, have been determined. It is shown that the main contribution to changes in the conversion function and sensor sensitivity is made by the change in the negative differential resistance with a change in temperature. This, in turn, results in different readings of the instrument’s output frequency. The sensor sensitivity was varied from 480 kHz/0С to 220 kHz/0С in the temperature range from -150 0С to 50 0С.

New types of resonant tunneling currents at Si-p/n junctions: one-dimensional model calculation

New types of resonant tunneling currents at Si-p/n junctions, which are caused by the resonance between the donor and acceptor-dopant states and by the resonance states in a triangular quantum-well-like potential in the p/n junctions, are studied by a time-evolution simulation of electron wave packets. It is shown that the tunneling currents are enhanced by these resonances because the resonance states work as step stones for the inter-band tunneling transitions and the effective tunneling distance becomes short. We also show that such enhancement of tunneling currents can occur in not only indirect band-gap Si systems but also direct band-gap semiconductor systems.

Spin-Filter Devices Based on Resonant Magnetic Tunnel Junctions

Spin-polarized currents are investigated in symmetric (asymmetric) resonant magnetic tunnel junctions (S- (A)-RMTJs) including a non-magnetic metal (NM) layer. Charge-diode and spin-diode features are found for the S-RMTJs at definite thicknesses of MgO and NM layers. Owing to the presence of quantum-well states, a full spin polarization can be achieved by proper choice of the thickness of NM layer. The charge and spin currents have increased for the A-RMTJs in comparison to those of the S-RMTJs due to different properties of ferromagnetic electrodes. The present study suggests new spin-filter devices to use in the spintronics field.