Resonant Tunneling Structures Research Articles

Effects of Pressure on GaAs/InxGa1-xAs/AlAs Resonant Tunneling Structures

Effects of Pressure on GaAs/InxGa1-xAs/AlAs Resonant Tunneling Structures

On the effect of the electron distribution in the near-contact region and asymmetry of the resonant-tunneling diode structure on the high-frequency response and the possibility of detecting the quantum amplification mode in an external high-frequency electric field

The conditions of the implementation of the quantum mode of microwave generation in semiconductor resonant-tunneling diode (RTD) structures were theoretically analyzed. The high-frequency response in structures with symmetric and asymmetric barriers was analyzed by numerical simulation methods. The effect of the Fermi distribution of carriers in the near-contact region was studied. It was shown that asymmetric structures with decreased impurity concentrations (1017 cm−3) in the emitter region are optimum from the viewpoint of experimental observation of the quantum amplification mode.

High-frequency response and the possibility of detecting the quantum amplification mode in resonant-tunneling diode structures

The conditions of the implementation of the quantum mode of microwave generation in semiconductor resonant-tunneling diode (RTD) structures were theoretically analyzed. Based on the constructed analytical model of the steady-state current and high-frequency response in symmetric RTD structures with finite barrier widths, high-frequency properties of RTDs in an external ac electric field were analyzed by numerical simulation methods. It was shown that the quantum amplification mode can appear not only in the high-frequency region of the terahertz range, but also at relatively low frequencies due to deformation of frequency dependences in a dc electric field.

Dependence of current–voltage characteristics of pseudomorphic AlAs/In0.53Ga0.47As/InAs resonant tunnelling diodes on quantum well widths

This paper studies the dependence of I – V characteristics on quantum well widths in AlAs/In0.5<3Ga0.47As and AlAs/In0.53Ga0.47As/InAs resonant tunnelling structures grown on InP substrates. It shows that the peak and the valley current density in the negative differential resistance region are closely related with quantum well width. The measured peak current density, valley current densities and peak-to-valley current ratio of resonant tunnelling diodes are continually decreasing with increasing well width.

On the theory of the resonant interaction of electrons with a high-frequency electric field in one-dimensional two-barrier nanostructures with symmetric barriers of finite height and width

The theory of the interaction of electrons with a high-frequency electric field in one-dimensional two-barrier nanostructures with symmetric barriers of finite height and widths was developed. An exact solution to the Schrodinger equation was found for electrons in this nanostructure in the absence of high-frequency electric field. An analytical expression for the direct current I0 induced in this structure by an incident electron flux with energy e differing slightly from the resonant level energy er(|e − er| er, the current Ic is negative in the entire frequency range, which suggests the possibility of ac electric field amplification and generation in the two-barrier resonant-tunneling structure with the barriers of finite height and width. Within the applicability of the theory (ℏω << er), the frequency at which amplification and generation of the ac electric field are possible reaches ω ≳ 1013s−1; the power transferred by electrons to the field is ∼1 W/cm2.

Quantum dots for terahertz generation

Nanostructures made of semiconductors, such as quantum wells and quantum dots (QD),are well known, and some have been incorporated in practical devices. Here we focus onnovel structures made of QDs and related devices for terahertz (THz) generation. Theirpotential advantages, such as low threshold current density, high characteristictemperature, increased differential gain, etc, make QDs promising candidates for lightemitting applications in the THz region. Our idea of using resonant tunneling through QDsis presented, and initial results on devices consisting of self-assembled InAs QDs in anundoped GaAs matrix, with a design incorporating a GaInNAs/GaAs short periodsuperlattice, are discussed. Moreover, shallow impurities are also being explored forpossible THz emission: the idea is based on the tunneling through bound states ofindividual donor or acceptor impurities in the quantum well. Initial results on deviceshaving an AlGaAs/GaAs double-barrier resonant tunneling structure are discussed.

Self-sustained Magnetoelectric Oscillations in Magnetic Resonant Tunneling Structures

The dynamic interplay of transport, electrostatic, and magnetic effects in the resonant tunneling through ferromagnetic quantum wells is theoretically investigated. It is shown that the carrier-mediated magnetic order in the ferromagnetic region not only induces, but also takes part in intrinsic, robust, and sustainable high-frequency current oscillations over a large window of nominally steady bias voltages. This phenomenon could spawn a new class of quantum electronic devices based on ferromagnetic semiconductors.

Laterally coupled self-assembled InAs quantum dots embedded in resonant tunnel diode with multigate electrodes

We study the electronic properties of submicron vertical resonant tunneling structures containing several self-assembled InAs quantum dots (SADs) surrounded by four gate electrodes. The four gates are designed not only to squeeze the conductive channel containing a few SADs but also to differently modulate the electrochemical potential of each SAD. We measure the stability diagram and distinguish the features of lateral interdot coupling, such as the type of coupling (quantum mechanical or capacitive), the number of coupled dots, and the relative coupled dot position. This technique will be useful in characterizing the electronic properties of coupled SAD systems.

Mesopiezoresistive effects in double-barrier resonant tunneling structures

This letter reports a mesopiezoresistive effect in a double-barrier resonant tunneling (DBRT) structure. In a DBRT system, an external mechanical stress causes a tensile strain, and the strain, in turn, affects the resonant tunneling and thereby the resistance. Theoretical analysis was carried out on an AlAs∕GaAs∕AlAs DBRT structure under in-plane uniaxial tensile stresses. The results show that the tunneling current and resistance of a DBRT structure change significantly with external stress-induced tensile strains. The results also show that the resistance-strain response can be tuned effectively by the external voltage. The effect has potential applications in miniature electromechanical devices.

Meso-piezo-resistive Effect and Devices

The meso-piezoresistive effect of GaAs/AlAs/InGaAs double barrier supper-lattice thin films and some new types of sensor based on this effect are introduced.The four steps of meso-piezoresistive effect are demonstrated,and the GaAs/AlAs/InGaAs resonant tunneling structure(RTS)is processed on[001]crystal orientation semi-insulating substrate.Pressure measurements show that its meso-piezoresistive sensitivity reaches 2.54×10~(-9)Pa~(-1),which is an order higher than that of silicon.The Nano-electromechanical sensors,such as membrane pressure sensor,four-beam accelerometer and bionic vector hydrophone,are fabricated successfully by micro control-hole technology,and they are measured in pressure tank,vibration table and standing wave tube respectively.Measurement results show that the membrane pressure sensor has good electro-mechanical coupling characteristics; the piezoresistive sensitivity of four-beam accelerometer can be adjusted by the biased voltage of RTS,and the largest sensitivity is in the negative differential resistance(NDR)region;The vector hydrophone has excellent8cosine directivity,and its sensitivity reaches-184.6 dB at 1 000 Hz.which can realize horizontal underwater sound signal detection.

Current and shot noise in double barrier resonant tunneling structures in a longitudinal magnetic field

Current and shot noise in double barrier resonant tunneling structures in a longitudinal magnetic field

Well-defined electrical properties of high-strain resonant interband tunneling structure

The GaAs/InAs high-strain resonant interband tunneling diodes (HSRITDs) have been implemented by metal organic chemical vapor deposition (MOCVD). The current–voltage characteristics of variable quantum well and barrier thickness grown on (1 1 1) GaAs substrates are investigated. Experimental results reveal that the quantum barrier and well layer will influence current–voltage properties such as the peak current density, valley current density, and peak-to-valley current ratio (PVCR). Both peak current and valley current density decrease with increasing layers width. This result also exhibits the variation of PVCR with layers width.

Selective energy contacts for hot carrier solar cells

The concept of the hot carrier cell is to absorb a wide range of photon energies and to separate the resulting “hot” carriers before thermalisation within a narrow range of energies onto external electrodes. Proof of concept of selective energy contacts has been demonstrated for double barrier resonant structures using Si quantum dots for resonant energy levels using current–voltage measurement with and without optical excitation and conductive atomic force microscopy. Si quantum dot resonant tunnelling structures are fabricated by thin film deposition followed by Si solid state precipitation in a SiO 2 matrix, with the size uniformly controlled by the layer thickness. Further characterisation and approaches to optimization are discussed.

Current shot noise characteristics in resonant tunneling step-barrier structures

The current shot noise behavior in resonant tunneling step-barrier structures is investigated based on the standard scattering approach. The relations between the shot noise and the applied bias, the Fermi energies, as well as the structural parameters are revealed. By making a comparison of resonant tunneling among single square-barrier structures, step-barrier structures, and double-barrier structures, the distinct curve shape and extremely large suppression of the shot noise are revealed in the step-barrier structures. It is shown that in the step-barrier structures, a valley of the shot noise occurs at the bias where the current peak locates and the Fano factor drops down to minimum at the valley bottom. It is also found that the shot noise suppression is larger for larger chemical potentials and maximal suppression with the Fano factor close to 0.05 appears at a particular structure configuration. These results are helpful to improve the signal-to-noise ratio of quantum devices based on resonant-tunneling structures.

Scattering approach to current and noise in interacting mesoscopic systems

We propose an extension of the Landauer-Buttiker scattering theory to include effects of interaction in the active region of a mesoscopic conductor structure. The current expression obtained coincides with those derived by different methods. A new general expression for the noise is also established. These expressions are then discussed in the case of strongly sequential tunneling through a double-barrier resonant tunneling structure.

Semiconductor spintronics

Semiconductor spintronicsSpintronics refers commonly to phenomena in which the spin of electrons in a solid state environment plays the determining role. In a more narrow sense spintronics is an emerging research field of electronics: spintronics devices are based on a spin control of electronics, or on an electrical and optical control of spin or magnetism. While metal spintronics has already found its niche in the computer industry—giant magnetoresistance systems are used as hard disk read heads—semiconductor spintronics is yet to demonstrate its full potential. This review presents selected themes of semiconductor spintronics, introducing important concepts in spin transport, spin injection, Silsbee-Johnson spin-charge coupling, and spin-dependent tunneling, as well as spin relaxation and spin dynamics. The most fundamental spin-dependent interaction in nonmagnetic semiconductors is spin-orbit coupling. Depending on the crystal symmetries of the material, as well as on the structural properties of semiconductor based heterostructures, the spin-orbit coupling takes on different functional forms, giving a nice playground of effective spin-orbit Hamiltonians. The effective Hamiltonians for the most relevant classes of materials and heterostructures are derived here from realistic electronic band structure descriptions. Most semiconductor device systems are still theoretical concepts, waiting for experimental demonstrations. A review of selected proposed, and a few demonstrated devices is presented, with detailed description of two important classes: magnetic resonant tunnel structures and bipolar magnetic diodes and transistors. In view of the importance of ferromagnetic semiconductor materials, a brief discussion of diluted magnetic semiconductors is included. In most cases the presentation is of tutorial style, introducing the essential theoretical formalism at an accessible level, with case-study-like illustrations of actual experimental results, as well as with brief reviews of relevant recent achievements in the field.

Momentum filter using resonant Zener tunneling

We consider the formation of a double barrier structure which includes both the valence and conduction bands in an $\mathrm{In}\mathrm{Sb}∕\mathrm{In}\mathrm{Al}\mathrm{Sb}$ quantum well system and demonstrate basic features of the transport process through this structure, which exhibits Zener tunneling. In particular, we employ an eight-band model and the Landauer-B\"uttiker formalism [Phys. Rev. B 31, 6207 (1985)] to investigate the transport process which under high confinement involves resonant energy levels due to the induced quasibound states in the valence bands. The mechanism of momentum filtering, taking advantage of resonant Zener tunneling, is shown to give improved performance at elevated temperatures compared with a unipolar double barrier resonant tunneling structure.

Phonon-induced shot noise enhancement in resonant tunneling structures

Using the nonequilibrium Green’s function formalism, the authors investigate the effect of the electron-phonon interaction on the current and shot noise in one dimensional resonant tunneling structures. Besides the well-known current behavior, they particularly show that the shot noise may be enhanced over the Poissonian value due to the phonon-assisted tunneling effect. The observed super-Poissonian noise is then interpreted as a result of the competition between the coherent and sequential current components.

Photoluminescence characterization technique for resonant-tunneling structures based on a long-period GaAs/AlGaAs superlattice, applicable at different stages of fabrication

A technique is developed for the photoluminescence-spectroscopy characterization of resonant-tunneling structures based on a long-period GaAs/AlGaAs superlattice that can be used for quality evaluation at all the stages of fabrication, including molecular-beam epitaxy, photolithography, and annealing. Factors such as the small energy difference between the quantum confined states in wide quantum wells, which make the photoluminescence characterization of such structures more difficult are taken into account. The long-period multiquantum-well structures are promising for the development of a new kind of solid-state intersub-band-transition devices emitting the narrow band radiation in far infrared. Their potential is essentially based on the fact that the scattering and the decay of carriers in the lower quantum-confined states may or may not involve optical phonons. The technique works at both liquid-helium and room temperature. It helps one optimize the process conditions to fabricate high-quality wide-quantum-well structures with excellent uniformity and desired parameters.

Spin-Polarized Transport in II–VI Magnetic Resonant-Tunneling Devices

This paper investigates electronic transport through II-VI semiconductor resonant-tunneling structures containing diluted magnetic impurities. Due to the exchange interaction between the conduction electrons and the impurities, there arises a giant Zeeman splitting in the presence of a moderately low magnetic field. As a consequence, when the quantum well is magnetically doped, the current-voltage characteristics show two peaks corresponding to transport for each spin channel. This behavior is experimentally observed and can be reproduced with a simple tunneling model. The model thus allows to analyze other configurations. First, the magnetic field was further increased, which leads to a spin polarization of the electronic current injected from the leads, thus giving rise to a relative change in the current amplitude. The authors demonstrate that the spin polarization in the emitter can be determined from such a change. Furthermore, in the case of an injector with magnetic impurities, the model shows a large increase in peak amplitude accompanied by a shift of the resonance to higher voltages with increasing fields. It was found that this effect arises from a combination of 3D incident distribution, giant Zeeman splitting, and broad resonance linewidth