Resonant Tunneling Phenomena Research Articles

Influence of the active region structure of the resonant tunneling diode on the critical points of its current-voltage characteristic

The article proposes a study of the effect of the structure of the active region of a resonant tunneling diode on the critical points of its current-voltage characteristic. The basic configuration of a resonant tunneling diode, which is a structure of a quantum well with a nanometer-sized double barrier including two contacts, and a region with strongly doped contacts made of a semiconductor with a relatively small band gap, is disclosed and illustrated. It is emphasized that since the characteristic dimensions of the structure of the quantum well with a double barrier are comparable to the wavelengths of electrons, the wave nature of electrons leads to such quantum phenomena as interference, tunneling, energy quantization, etc. the double barrier causes resonant tunneling phenomena, which form the basis for the operation of the resonant-tunneling diode. It is emphasized that repeated reflection causes destructive or constructive interference depending on the wavelength of a particular electron. For electrons with a certain wavelength that promotes constructive interference, a transfer probability close to unity can be found at energies corresponding to these wavelengths. The modification of the active region of the resonant tunnel diode with a barrier height of 0.3 - 0.4 eV is mathematically substantiated. The dependence of the transmission coefficient is found by solving the Schrödinger equation in one electron approximation without taking into account the scattering effects. The calculation of the volt-ampere characteristic of the resonant-tunnel diode was performed at temperatures of 100 and 300 K. The given volt-ampere characteristics were obtained without taking into account the effects of electron scattering. However, it should be noted that the main influencing factor is the resonant tunneling through the second level, for which the peak of the transmission coefficient is much wider and higher. However, in gallium doped arsenide, the fact of electron scattering can significantly affect the value of the transmission coefficient and the value of current. It is established that an increase in the width of quantum wells leads to a significant decrease in the densities of peak currents and valley currents, and an increase in the width of potential barriers leads to a slight decrease in the current density of the first peak and current densities of the second peak and valley.

Longitudinal and transversal resonant tunneling of interacting bosons in a two-dimensional Josephson junction

We unravel the out-of-equilibrium quantum dynamics of a few interacting bosonic clouds in a two-dimensional asymmetric double-well potential at the resonant tunneling scenario. At the single-particle level of resonant tunneling, particles tunnel under the barrier from, typically, the ground-state in the left well to an excited state in the right well, i.e., states of different shapes and properties are coupled when their one-particle energies coincide. In two spatial dimensions, two types of resonant tunneling processes are possible, to which we refer to as longitudinal and transversal resonant tunneling. Longitudinal resonant tunneling implies that the state in the right well is longitudinally-excited with respect to the state in the left well, whereas transversal resonant tunneling implies that the former is transversely-excited with respect to the latter. We show that interaction between bosons makes resonant tunneling phenomena in two spatial dimensions profoundly rich, and analyze these phenomena in terms of the loss of coherence of the junction and development of fragmentation, and coupling between transverse and longitudinal degrees-of-freedom and excitations. To this end, a detailed analysis of the tunneling dynamics is performed by exploring the time evolution of a few physical quantities, namely, the survival probability, occupation numbers of the reduced one-particle density matrix, and the many-particle position, momentum, and angular-momentum variances. To accurately calculate these physical quantities from the time-dependent many-boson wavefunction, we apply a well-established many-body method, the multiconfigurational time-dependent Hartree for bosons (MCTDHB), which incorporates quantum correlations exhaustively. By comparing the survival probabilities and variances at the mean-field and many-body levels of theory and investigating the development of fragmentation, we identify the detailed mechanisms of many-body longitudinal and transversal resonant tunneling in two dimensional asymmetric double-wells. In particular, we find that the position and momentum variances along the transversal direction are almost negligible at the longitudinal resonant tunneling, whereas they are substantial at the transversal resonant tunneling which is caused by the combination of the density and breathing mode oscillations. We show that the width of the interparticle interaction potential does not affect the qualitative physics of resonant tunneling dynamics, both at the mean-field and many-body levels. In general, we characterize the impact of the transversal and longitudinal degrees-of-freedom in the many-boson tunneling dynamics at the resonant tunneling scenarios.

A Voltage-Controlled Gain Cell Magnetic Memory

This letter presents a magnetic gain cell structure that consists of a new kind of voltage-controlled magnetic tunnel junction (MTJ) and two transistors for a large separation in the output current for the two memory states while retaining the low power advantages of a voltage-controlled write mechanism. The voltage-controlled MTJ utilizes the interlayer exchange coupling and the resonant tunneling phenomena to enable a resonant-exchange-controlled (REC) magnetization switching, leading to a substantially low write energy and delay, in the order of 29.5 fJ/bit and 1.6 ns, respectively. Two transistors in a gain cell configuration can provide a 103 times change in the output current between the 0 and 1 states from a ~25% magnetoresistance of the REC MTJ with a high baseline resistance in the order of a few $\text{M}\Omega $ . Such a magnetic gain-cell also exhibits low read energy and delay, in the range of 7.6~39 fJ/bit and 0.6~1 ns, thus promising for low energy, fast, and high-density memory technologies.

Antidote-induced armchair graphene nanoribbon based resonant tunneling diodes

Resonant tunneling phenomena are explored using armchair graphene nanoribbon (AGNR), which eliminates the lattice mismatch and electron mobility degradation problems of conventional heterostructure resonant tunneling diodes (RTDs). Eight antidote topologies are proposed in this paper. These antidote topologies significantly increase or decrease the band gap of AGNR. Both double barrier quantum well and single barrier quantum well structures have been achieved by putting the antidote-induced AGNRs and pristine AGNRs. A numerical approach with a tight binding model and non-equilibrium Green’s function formalism has been used to simulate the quantum phenomena of the device. Current–voltage characteristics of these proposed RTDs show a high peak to valley ratio and low power dissipation with respect to different antidote topologies. Channel length variation effects are investigated in the proposed RTDs, and it is found that the peak to valley ratio, valley current, valley voltage, and power dissipation can be improved by tuning the channel length. These graphene-based RTDs are easy to fabricate and offer more flexibility in terms of peak to valley ratio, valley current, valley voltage, and power dissipation.

N-polar GaN/AlN resonant tunneling diodes

N-polar GaN/AlN resonant tunneling diodes are realized on a single-crystal N-polar GaN bulk substrate by plasma-assisted molecular beam epitaxy growth. The room-temperature current–voltage characteristics reveal a negative differential conductance (NDC) region with a peak tunneling current of 6.8 ± 0.8 kA/cm2 at a forward bias of ∼8 V. Under reverse bias, the polarization-induced threshold voltage is measured at ∼−4 V. These resonant and threshold voltages are well explained with the polarization field, which is opposite to that of the metal-polar counterpart, confirming the N-polarity of the resonant tunneling diodes (RTDs). When the device is biased in the NDC-region, electronic oscillations are generated in the external circuit, attesting to the robustness of the resonant tunneling phenomenon. In contrast to metal-polar RTDs, N-polar structures have the emitter on the top of the resonant tunneling cavity. As a consequence, this device architecture opens up the possibility of seamlessly interfacing—via resonant tunneling injection—a wide range of exotic materials with III-nitride semiconductors, providing a route towards unexplored device physics.

Resonant Enhancement of Exchange Coupling for Voltage-Controlled Magnetic Switching

We propose an electric-field-controlled mechanism for magnetization switching assisted solely by the interlayer-exchange coupling (IEC) between the fixed and the free magnets, which are separated by two oxide barriers sandwiching a spacer material known for exhibiting large IEC. The basic idea relies on the formation of a quantum-well (QW) within the spacer material and controlling the transmission coefficient across the structure with an electric-field via the resonant tunneling phenomena. Using non-equilibrium Green's function (NEGF) method, we show that the structure can exhibit a bias-dependent oscillatory IEC that can switch the free magnet to have either a parallel or an antiparallel configuration with respect to the fixed magnet, depending on the sign of the IEC. Such bi-directional switching can be achieved with the same voltage polarity but different magnitudes. With proper choice of the spacer material, the current in the structure can be significantly reduced. Due to the conservative nature of the exerted torque by the IEC, the switching threshold of the proposed mechanism is decoupled from the switching speed, while the conventional spin-torque devices exhibit a trade-off due to the non-conservative nature of the exerted torque.

Harmonic instability in a quantum cascade laser with Fabry–Perot cavity

A new state of instability called harmonic instability, which is characterized by the appearance of side modes separated by multiple of free spectral range from each other, was discovered in quantum cascade lasers (QCLs) a few years ago. However, a detailed analysis using a model beyond the two-level density-matrix (DM) equations as well as incorporating phenomena such as the detuning of the primary-mode frequency from the line-center frequency and the frequency dependence of the background refractive index, resulting in group velocity dispersion (GVD), has not been performed yet. In this paper, we present a comprehensive analysis of harmonic instability in a QCL with a Fabry–Perot (FP) cavity. Starting from three-level DM equations, which include the resonant tunneling phenomenon and scattering rates between all three states, and then by using Maxwell's equation, we derive a closed-form expression for the gain of the side modes, from which quantities pertinent to instability can be determined. We also take the aforementioned phenomena into account in our theory. By using our theory, we show the way of determining primary-mode detuning from the line center. Furthermore, we study the effects of GVD on instability in detail, showing that the output from an FP QCL demonstrates the characteristic of a frequency-modulated wave up to a certain value of dispersion. Above this value, because of the significant deviation of the side-mode amplitude ratio from unity, the output shows neither frequency-modulated-like nor amplitude-modulated-like behavior.

Resonant Tunneling and Negative Differential Resistance in Black Phosphorus Vertical Heterostructures

AbstractResonant tunneling diodes with negative differential resistance (NDR) have attracted significant attention due to their unique quantum resonant tunneling phenomena and potential applications in terahertz emission/detection and high‐density logic/memory. In this paper, resonant tunneling devices, where the carriers tunnel through a hexagonal boron nitride (hBN) barrier sandwiched by two black phosphorus (BP) layers, are explored. The resonance occurs when the energy bands of the two black phosphorus layers are aligned. The conductive atomic force microscopy (CAFM) measurements reveal prominent NDR peaks with large peak‐to‐valley ratios at room temperature. It is found that the positions of the NDR peaks are very sensitive to the amplitude and the shape of the voltage waveform used in CAFM, which can be explained by the charge trapping effect. Furthermore, resonant tunneling transistors are demonstrated based on BP/hBN/BP stacks in which the locations of the NDR peaks are tunable by the electrostatic gating. As compared to the traditional tunneling diodes based on bulk materials, the tunneling devices based on thin boron nitride tunneling barrier and high mobility black phosphorus offer ultra‐high‐speed response. This feature, together with the NDR characteristics, provides the potential for applications in THz oscillators and multi‐value logic devices.

Broken Symmetry Effects due to Polarization on Resonant Tunneling Transport in Double-Barrier Nitride Heterostructures

The phenomenon of resonant tunneling transport through polar double-barrier heterostructures is systematically investigated using a combined experimental and theoretical approach. On the experimental side, GaN/AlN RTDs are grown by MBE. In-situ electron diffraction is employed to monitor the number of monolayers incorporated into each tunneling barrier. Using this precise epitaxial control at the monolayer level, we demonstrate exponential modulation of the resonant tunneling current as a function of barrier thickness. Both the peak voltage and characteristic threshold bias exhibit a dependence on barrier thickness as a result of the intense electric fields present in the polar heterostructures. To get further insight into the asymmetric tunneling injection, we present an analytical theory for tunneling transport across polar heterostructures. A general expression for the resonant tunneling current with contributions from coherent and sequential tunneling processes is introduced. After applying this theory to the case of GaN/AlN RTDs, their experimental current-voltage characteristics are reproduced over both bias polarities, with tunneling currents spanning several orders of magnitude. This agreement allows us to elucidate the role played by the internal polarization fields on the magnitude of the tunneling current and broadening of the resonant line shape. Under reverse bias, we identify new tunneling features originating from highly attenuated resonant tunneling phenomena, which are completely captured by our model. Our analytical model, provides a simple expression which reveals the connection between the polar RTD design parameters and its current-voltage characteristics. This new theory paves the way for the design of polar resonant tunneling devices exhibiting efficient resonant current injection and enhanced tunneling dynamics, as required in various practical applications.

Magnon resonant tunneling effect in double-barrier insulating magnon junctions and magnon field effect transistor

We predict a magnonic resonant tunneling phenomenon in the double-barrier insulating magnon junctions of ${\text{FI}}_{1}/{\text{AFI}}_{1}/{\text{FI}}_{2}/{\text{AFI}}_{2}/{\text{FI}}_{3}$, where ${\text{FI}}_{(1,2,3)}$ and ${\text{AFI}}_{(1,2)}$ denote the ferromagnetic and antiferromagnetic insulating layers, respectively. Similar to electron tunneling in well-known double-barrier magnetic tunnel junctions, each antiferromagnetic insulator layer acts as an effective potential barrier for magnons due to its intrinsically large magnon-spectrum gap of the order of THz. Based on the magnon tunneling effect, we further propose a magnon field effect transistor that is capable of realizing a gate-tunable transmitted magnon flow by tuning the resonant tunneling via a gate electric field induced Dzyaloshinskii-Moriya interaction in the middle FI layer. The advantages of such transistors include their broadband frequency width ranging from GHz to THz at room temperature, high scalability, and intrinsic low dissipation without Joule heating loss.

Comparison of the I–V characteristics of a topological insulator quantum well resonant tunneling transistor and its conventional counterpart: A TCAD simulation study

In this study, we investigated and simulated the structure of a quantum well resonant tunneling (QWRT) transistor based on two barriers and a well in the middle. The barriers were formed of semiconductors with a higher bandgap and the well separating the barriers comprised a semimetal-like material with a very small bandgap, i.e., close to zero. The device was positioned on the oxide to exploit the benefits of SOI technology, e.g., improving leakage and the immunity of the device against environment effects. When the well thickness was a few nanometers, the electron-bound states appeared in the quantum well region. By tuning the voltage and work function of the top gate, the bound states moved in the potential well and the carriers were transferred through the well via the resonant tunneling phenomenon. Our simulations showed the step-like behavior of the output characteristics and the oscillatory quantum switching of the transfer characteristics for the proposed device. We also investigated the influence of the well thickness and gate voltage on the device characteristics, and we compared the optimal case with a theoretical analysis of a QWRT transistor based on a topological insulator.

Atomic-Monolayer Two-Dimensional Lateral Quasi-Heterojunction Bipolar Transistors with Resonant Tunneling Phenomenon.

High-frequency operation with ultrathin, lightweight, and extremely flexible semiconducting electronics is highly desirable for the development of mobile devices, wearable electronic systems, and defense technologies. In this work, the experimental observation of quasi-heterojunction bipolar transistors utilizing a monolayer of the lateral WSe2-MoS2 junctions as the conducting p-n channel is demonstrated. Both lateral n-p-n and p-n-p heterojunction bipolar transistors are fabricated to exhibit the output characteristics and current gain. A maximum common-emitter current gain of around 3 is obtained in our prototype two-dimensional quasi-heterojunction bipolar transistors. Interestingly, we also observe the negative differential resistance in the electrical characteristics. A potential mechanism is that the negative differential resistance is induced by resonant tunneling phenomenon due to the formation of quantum well under applying high bias voltages. Our results open the door to two-dimensional materials for high-frequency, high-speed, high-density, and flexible electronics.

Resonant tunneling of illuminated multi-insulator diodes

The current–voltage (I–V) characteristics of two different Metal–Insulator–Metal (MIM) diodes with three insulator layers were calculated and compared. The effect of illumination, or the photon-assisted tunneling was considered with the Tien–Gordon model. Our calculations indicate that, by carefully designing the insulating layers of the MIM diodes, the resonant tunneling phenomena can be tuned effectively in the diodes with quantum well structures. The results also show that the minimum shift of the illuminated current depends not only on the intensity of the photons incident but also on the diode structures, or the parameters of the insulators and so on.

Macroscopic resonant tunneling in an rf-SQUID flux qubit under a single-cycle sinusoidal driving**Project supported by the National Natural Science Foundation of China (Grant Nos. 11474154, 61371036, 61571219, 11227904, and 61501222) and the Natural Science Fund for Distinguished Young Scholars of Jiangsu Province, China (Grant No. BK2012013) and PAPD.

We experimentally demonstrate the observation of macroscopic resonant tunneling (MRT) phenomenon of the macroscopic distinct flux states in a radio frequency superconducting quantum interference device (rf-SQUID) under a single-cycle sinusoidal driving. The population of the qubit exhibits interference patterns corresponding to resonant tunneling peaks between states in the adjacent potential wells. The dynamics of the qubit depends significantly on the amplitude, frequency, and initial phase of the driving signal. We do the numerical simulations considering the intra-well and inter-well relaxation mechanism, which agree well with the experimental results. This approach provides an effective way to manipulate the qubit population by adjusting the parameters of the external driving field.

Electrical measurement of the linewidth of a quantum well bound state

We investigate electron tunneling spectroscopy in the presence of a bound state within a double quantum barrier, single quantum well structure. We demonstrate a new technique to directly measure the intrinsic linewidth of the bound state within the quantum well from the current-voltage signature of the resonant tunneling phenomena and contrast our results with the standing approach in the literature. We then examine the signal behavior for the influence of device temperature and find support for electron-electron interactions within the well. The measured intrinsic bound-state width, ΓE, in the negative differential conductance regime is 1.11± 0.01 meV.

Resonant electron tunneling and related charging phenomena in metal–oxide–p +-Si nanostructures

The j–V characteristics of the Al/thermal or electrochemical SiO2(2–4 nm)/heavily doped p +-Si nanostructures operating as a resonant-tunneling diode were measured and theoretically analyzed. The characteristics have specific features in the form of current steps and peaks, which are caused by electron transport between the silicon valence band and metal through discrete levels of the quantum well formed by the p +-Si conduction band and SiO2/p +-Si interface. Resonant tunneling through the surface state levels and the appearance of a charge near this interface under certain conditions are discussed.

Long-Range Phase Coherence in Double-Barrier Magnetic Tunnel Junctions with a Large Thick Metallic Quantum Well

Double-barrier heterostructures are model systems for the study of electron tunneling and discrete energy levels in a quantum well (QW). Until now resonant tunneling phenomena in metallic QWs have been observed for limited thicknesses (1-2 nm) under which electron phase coherence is conserved. In the present study we show evidence of QW resonance states in Fe QWs up to 12 nm thick and at room temperature in fully epitaxial double MgAlO_{x} barrier magnetic tunnel junctions. The electron phase coherence displayed in this QW is of unprecedented quality because of a homogenous interface phase shift due to the small lattice mismatch at the Fe-MgAlO_{x} interface. The physical understanding of the critical role of interface strain on QW phase coherence will greatly promote the development of spin-dependent quantum resonant tunneling applications.

Tunneling of Atoms, Nuclei and Molecules

This is a brief review of few relevant topics on tunneling of composite particles and how the coupling to intrinsic and external degrees of freedom affects tunneling probabilities. I discuss the phenomena of resonant tunneling, different barriers seen by subsystems, damping of resonant tunneling by level bunching and continuum effects due to particle dissociation.

Optical isolation via one-dimensional magneto-photonic crystals containing nonlinear defect layer

In this paper we investigate the transmission properties of one-dimensional periodic structures containing magneto-optical (MO) material layers with a nonlinear defect layer using the transfer matrix method. It is shown that such structures can exhibit unidirectional resonant photon tunneling phenomena which can discriminate between circularly polarized (CP) wave of given handedness impinging from the same direction for specific incident field intensity. These structures may be utilized to design intensity dependent optical isolator for CP waves. Also it is demonstrated that the threshold intensity to achieve optical bistability depends on the bias magnetic field.

Transmission time and resonant tunneling through barriers using localized quantum density soliton waves

In this paper, the interaction and transmission time of quantum density solitons waves [B. M. Mirza, Mod. Phys. Lett. B 28 (2014) 1450200]1 passing through finite barrier potentials is investigated. Using the conservation of energy and of quantum density, it is first demonstrated that the soliton waves possess the important particle-like properties, including localization by a finite de Broglie wavelength and constant uniform motion in free space. The passage of quantum density solitons through barriers of finite energies is then shown to lead to the phenomena of resonant tunneling and, in Josephson-like configurations, to the quantization of magnetic flux. A precise general measure for barrier tunneling time is derived which is found to give a new interpretation of the quantum indeterminacy principles. The quantum density soliton theory is applied to coherent microstructures observed in NbSe 3-like systems, where it is shown to lead to the sawtooth current phenomena and nano-scale transversal times.