Double Barrier Resonant Tunneling Device Research Articles

Negative differential resistance in conductive polymer and semiconducting quantum dot nanocomposite systems

We report the room temperature negative differential resistance (NDR) phenomenon in nanocomposite heterostructures made of semiconducting quantum dots embedded in conductive polymers. The peak to valley ratio of the current is 91 at room temperature which increases to 2965 at 77 K. The current voltage characteristics are simulated for a double barrier resonant tunneling device formed by semiconducting quantum dots and polymer molecules. The temperature dependence is also simulated and compared with the experimental results. A close agreement is found for the experimental and the simulation results for the location of the NDR peaks.

Effects of scattering resonances on carrier-carrier entanglement in charged quantum dots

We address the problem of the entanglement generation in an electron-scattering by a 1D double-barrier resonant tunnelling device. In particular we analyze the role played by transport resonances in the appearance of quantum correlations between the energy states of the electrons. The entanglement is not sensitive to the presence of Breit-Wigner resonances, while it may be controlled by manipulating Fano resonances. Such a behavior is ascribed to the different mechanisms characterizing the two types of processes.

Transport properties of a Ga1-xMn xAs/Ga1-yAl yAs double-barrier

We study the transport properties of a spin filter consisting of a double-barrier resonant tunneling device in which the well is made of a semimagnetic material. Even if the device could be made of several materials, we discuss here the case of a Ga1-xMnxAs/Ga1-yAlyAs system because it can be integrated into the well known AlAs/GaAs technology. We solve the Hamiltonian H = HK+HP+HE+HM+Hh-i+Hh-h. Its terms represent the kinetic energy, the double-barrier profile, the applied bias, the magnetic interaction, the hole-impurity attraction and the hole-hole repulsion, respectively. A very simple one-dimensional Green function is introduced to solve self-consistently the Poisson equation for the profile due to the charge distribution. A real space renormalization formalism is used to calculate exactly the currents. In a previous work we have shown that the Rashba effect is weak. Therefore the results show very well defined spin-polarized currents. Our results confirm that this system is a good device for spintronics.

A selfconsistent calculation of the transport properties of a double barrier spin filter

A double barrier resonant tunneling device in which the well is made of a semi-magnetic material can work as an efficient spin filter. Today it is possible to make semiconductors that are ferromagnetic at room temperature. Therefore the device studied here has a great potential to be used as a polarizer, an analyzer and other spintronic applications. We discuss here the case of a Ga1-xMn xAs/Ga1-yAl yAs system because it can be integrated into the well known AlGaAs/GaAs technology. Our tight-binding Hamiltonian includes the kinetic energy, the double-barrier profile, the electric field, the magnetic term, the hole-impurity and the hole-hole interactions. The profile and the charge distribution are calculated self-consistently. In previous works we studied this system by solving the Hamiltonian in the reciprocal space, in order to simplify the treatment of the Poisson equation for the charge distribution. Here we introduce a simple one dimensional Green function that permits to solve all terms in the real space. Besides, a real space renormalization formalism is used to calculate exactly the electronic currents for each spin polarization. The results confirm that the proposed system is a good device for spintronics.

Tuning bistability and current hysteresis in resonant-tunneling structures

We present a time-dependent quantum kinetic simulation on the nonequilibrium electron transport of the symmetrical and asymmetrical double-barrier resonant-tunneling devices with various thickness of barriers. We obtain two bistabilities and hystereses of current found in experiments. Our calculations show that the physical mechanisms are different for the two bistabilities. The first bistability is mainly due to the charge accumulation in the quantum well and the second bistability and hysteresis is related to the current oscillation. Increasing the thickness of the collector barrier can enhance the first bistability while decreasing that of the collector barrier will enhance the second bistability.

Metal–insulator-transition studied by single-electron tunneling

We present measurements of single-electron tunneling in a vertical GaAs/AlGaAs double-barrier resonant-tunneling device with a low emitter doping. The transport spectrum of our sample exhibits a series of differential conductance peaks which experience an exponential shift to higher voltages with magnetic fields beyond a critical magnetic field. We attribute this effect to a metal-insulator transition in our device. A detailed analysis of the temperature-dependence of this effect is shown.

Dynamical instability and switching of resonant tunneling device under terahertz radiation

Using the Wigner-Poisson transport model, we have theoretically investigated dynamical instability and transient behavior of a double barrier resonant tunneling device driven by a terahertz field. It is found that switching between different current states may be triggered by terahertz electromagnetic radiation. The transition between high- and low-current states could be explained by time-dependent energy-level coupling and nonlinear processes. The characteristic switching times correspond to the terahertz frequency range, suggesting that the system may potentially act as a terahertz switch.

Study on the current bistability and hysteresis in resonant-tunneling structures

We present a time-dependent quantum-kinetic study for the non-equilibrium electron transport properties of double-barrier resonant-tunneling devices. The approach is based on a self-consistent solution of Wigner equation and Poisson equation. We find intrinsic current fluctuations around the current turning point. These instabilities lead to three current irreversible regions, two current hystereses and one small inverse current change in the valley position of current, for the forward and backward bias sweep. The bias step applied on the device affects the width of each current irreversible regions and the current peak height of the middle region.

Characteristics of electron transport through vertical double-barrier quantum-dot structures: Effects of symmetric and asymmetric variations of the lateral confinement potentials

We report on a theoretical study of the electron transport through laterally-confined, vertical double-barrier resonant-tunneling (DBRT) structures, defined as one-dimensional (1D)-0D-1D systems, with a tunable lateral confinement. The current and the differential conductance of the systems are calculated and the influence caused by varying the lateral confinement on the device characteristics is investigated. Three representative systems are studied. First of all, a 1D-0D-1D device, symmetric with respect to the current flow, with a variable lateral confinement in the double-barrier quantum-well (DBQW) region, is investigated. This device would in an experimental setup correspond to the structure in which a thin, lateral metallic gate is placed in the DBQW region. Subsequently, calculations are performed for two asymmetric 1D-0D-1D devices, in which the strongest, but varying, lateral confinement is placed either in the collector or in the emitter region. In experiments, these two devices would correspond to the situations where a lateral metallic gate is positioned below or on top of the DBQW structure. The calculations predict several phenomena for the device characteristics. It is shown that as the lateral confinement increases, in addition to those normally observed current onsets and pinch-offs that move toward higher bias voltages, several current onsets and pinch-offs move towards lower bias voltages. These negative shifts of the current onsets and pinch-offs with increasing of the lateral confinement have so far not been expected for gated DBRT devices. It is also found that the threshold voltages, at which the current onsets and pinch-offs appear, depend strongly on the strength and position of the lateral confinement and on the Fermi levels in the collector and the emitter. The models that explain these predictions are presented and discussed.

Electron-phonon interaction in electronic tunneling: from sequential rate equations to a coherent description

We discuss the main theoretical approaches for the phonon-assisted tunneling in double barrier resonant tunneling devices and introduce a quantum coherent treatment based on the mapping of the many-body problem into a higher dimensional one-body system. Conditions for a maximized phonon-emission are established.

Tuning a resonance in Fock space: Optimization of phonon emission in a resonant-tunneling device

Phonon-assisted tunneling in a double barrier resonant tunneling device can be seen as a resonance in the electron-phonon Fock space which is tuned by the applied voltage. We show that the geometrical parameters can induce a symmetry condition in this space that can strongly enhance the emission of longitudinal optical phonons. For devices with thin emitter barriers this is achieved by a wider collector's barrier.

Conductance fluctuations in a double-barrier resonant tunneling device

We have investigated conductance fluctuations due to tunneling through impurity states in the quantum well of a double-barrier resonant tunneling device. The impurity states are donor-related and are associated with a low-density Si \ensuremath{\delta}-doping layer incorporated into the center plane of the quantum well. At constant temperature, the relative amplitude of the conductance fluctuations is determined by the absolute number of donor impurities in the well and is found to scale as $({\mathrm{SN}}_{d}{)}^{\ensuremath{-}1/2},$ where ${N}_{d}$ is the areal density of donor atoms in the well, and S is the area of the device. The typical voltage period of the fluctuations is determined by the larger of kT or the natural linewidth of the state. There is excellent quantitative agreement between the experimental results and an existing theoretical model for conductance fluctuations in this type of system.

Terahertz switching action of a double-barrier resonant tunneling device

The response of an asymmetric double barrier resonant device to the passage of terahertz radiation is discussed. Within the bistable region the radiation is able to turn the current flowing through the system on or off, with an onset that depends on the bias, the strength of the incoming radiation, and its frequency.

ORIGIN OF HYSTERESIS AND PLATEAU-LIKE BEHAVIOR OF THE I-V CHARACTERISTICS OF RESONANT TUNNELING DIODES

In terms of numerical calculation of the coupled Wigner function–Poisson equations, the explanation to the origin of hysteresis and plateau-like behavior of the I-V characteristics of double barrier resonant tunneling devices is put forth. Several basic physical factors play key roles in the process of electron tunneling. Among these the most important factors are the interference of the injected and the reflected electron waves which leads to the formation of an emitter quantum well, the coupling between the energy level in the main quantum well and that in the emitter quantum well, and the coupling between the energy level in the main quantum well and the conduction b and edge or the three-dimensional states in the emitter. The interplay of these factors determines the form of the I-V curve of the resonant tunneling structure. The coupling between the energy levels in the emitter quantum-well and the main quantum-well leads to the plateau behavior of the I-V curves. The strength of the coupling determines the average slope of the plateau-like region in the I-V curve. The bias domain that the coupling exists determines the length of the plateau-like structure in the I-V curve. The domain can be controlled by adjusting the width of the barriers. The hysteresis is shown to be a manifestation of the above-mentioned energy level coupling, the coupling between the energy level in the main quantum well and the conduction b and edge or the three-dimensional states in the emitter, and the quantitative accumulation and distribution of electrons in the emitter region. This work provides new insight for underst and ing the nonlinear I-V behavior and establishes a foundation for the future analysis of bistability and oscillation behavior in resonant tunneling structures.

Room Temperature ZnO/Zn0.8Mg0.2O Resonant Tunneling Devices For Microwave Applications

ABSTRACTA ZnO/Zn0.8Mg0.2O double barrier resonant tunneling device (DBRTD) is reported here for the first time. The structure consists of 6 nm ZnO quantum wells and 7 nm Zn0.8Mg0.2O barriers grown by pulsed laser deposition (PLD) on c-cut sapphire substrates. Negative differential resistance (NDR) peaks were obtained at room temperature. The structure is developed by using an indium-tin oxide (ITO) layer both as the back contact electrode and as an etch-stopping layer. The PLD growth quality, wet etching processing for developing the mesa structure, and the I-V characteristics of the device are reported.

Interface roughness: a reason of inaccessibility of the negative resistance region in resonant-tunneling devices

Interface roughness in double-barrier resonant-tunneling devices affects the lateral electron motion in the quantum well and can give rise to subsidiary subbands or quasibound states in the well. We demonstrate that a shoulder frequently appearing beyond the principal resonance peak in the current–voltage characteristic can result from the resonant tunneling via those states.

Cryogenic amplification system for ultra-low noise measurements

We present a low-cost ultra-low-noise cryogenic amplifier, which has been developed for the investigation of shot noise suppression and enhancement in double-barrier resonant-tunneling devices. Results of the noise measurements performed on the amplifier operating at liquid nitrogen temperature are discussed and compared to those obtained at room temperature.

Studies of Phonon-Assisted Tunnelling in a δ-Doped Double Barrier Resonant Tunnelling Device

We report measurements of the change in current induced by non-equilibrium phonons in a δ-doped double barrier resonant structure. In addition to the anti-Stokes and Stokes peaks resulting from tunnelling through the ground state of Si donors present in the well, two further peaks, C and D, are observed in magnetic fields >5 T. Peak D is attributed to phonon-assisted tunnelling between two Landau levels, while C may be attributable to heating effects.

Dynamics of Hot Electrons in ZnSe-ZnTe Double Barrier Heterostructures

In this paper we perform a detailed study of the transport of hot electrons in the double barrier heterostructures with the presence of a collector barrier. This system is considered as a double barrier resonant tunneling device. The electron is described by time-dependent Schrődinger equation, which allows ns to study detailed dynamics of the carriers. The influence of an energy step in the collector area of the device on the tunneling probability is investigated. The significant role of dissipation due to electron-phonon interactions is presented. PACS numbers: 03.65.-w, 73.40.Gk, 73.61.-r

Resonant tunnelling through D− states

We have studied tunnelling through Si donors incorporated in the quantum well of double barrier resonant tunnelling devices. In addition to a resonance associated with the ground state of a single donor (1s level), a novel donor-related resonance at a smaller binding energy is observed in high magnetic fields where it becomes dominant over the 1s resonance. We attribute this novel feature to a D-minus state of a shallow donor.