Resonant Tunneling Structures Research Articles

Control of a resonant tunneling structure by intense laser fields

The intense laser field effects on a resonant tunneling structure were studied using computational methods. The considered structure was a GaAs/InxGa1-xAs/Al0.3Ga0.7As/InyGa1-yAs/AlAs/GaAs well-barrier system. In the presence of intense laser fields, the transmission coefficient and the dwell time of the structure were calculated depending on the depth and the width of InGaAs wells. It was shown that an intense laser field provides full control on the performance of the device as the geometrical restrictions on the resonant tunneling conditions overcome. Also, the choice of the resonant energy value becomes possible depending on the field strength.

Optoelectronic characterization of carrier extraction in a hot carrier photovoltaic cell structure

A hot carrier photovoltaic cell requires extraction of electrons on a timescale faster than they can lose energy to the lattice. We optically and optoelectronically characterize two resonant tunneling structures, showing their compatability with hot carrier photovoltaic operation, demonstrating structural and carrier extraction properties necessary for such a device. In particular we use time resolved and temperature dependent photoluminescence to determine extraction timescales and energy levels in the structures and demonstrate fast carrier extraction by tunneling. We also show that such devices are capable of extracting photo-generated electrons at high carrier densities, with an open circuit voltage in excess of 1 V.

Detection of terahertz radiation by resonant tunneling nanoheterostructures

The phenomenon of terahertz radiation detection by resonant tunneling structures (RTSs) has been studied. The calculations of the changes ΔI0 in the direct current (DC) component I0 under the action of an alternating electric field were carried out by the solution of a nonstationary Schrodinger equation with a time-periodic electric field based on the Floquet mode expansion of the wave functions. The dependences of the DC component I0 in resonant tunneling structures on the frequency ν and AC signal amplitude Vac have been built. It is shown that the ΔI0 value in triple-barrier RTSs at resonance frequency hv ≈ Er2–Er1 (Er1 and Er2 are the energies of the size-quantized levels) can exceed a low-frequency value by more than an order of magnitude. The parameters of the structures have been optmized, in order to use them in the terahertz radiation detectors in the anbsence of an external bias. The possibility of tuning the resonance frequency in the terahertz range by changing the DC bias has been shown.

The photoinduced voltage shift behavior in three-barrier resonant tunneling structure

Resonant tunneling structures show negative differential resistance and enables many unique applications. Most researches have focused on structures with one or two barriers. In this paper, a three-barrier, two-well resonant tunneling structure integrated with a 1.2-µm-thick n-type GaAs layer are investigated numerically. The results show that the coupling between the energy level in the incident well and that in the central quantum well is the key point in understanding the origin of the current–voltage multi-peak at reverse bias. A photoinduced voltage shift manifests that the 1.2-µm-thick, slightly doped n-GaAs layer plays an important role in enhancing photoelectric sensitivity.

Excitation of plasmonic nanoantennas by nonresonant and resonant electron tunnelling.

A rigorous theory of photon emission generated by inelastic electron tunnelling inside the gap of plasmonic nanoantennas is developed. The disappointingly low efficiency of the electrical excitation of surface plasmon polaritons in these structures can be increased by orders of magnitude when a resonant tunnelling structure is incorporated inside the gap. A resonant tunnelling assisted surface plasmon emitter may become a key element in future electrically-driven plasmonic nanocircuits.

Vnesok dvofotonnykh elektronnykh perekhodiv u formuvannya aktyvnoyi dynamichnoyi providnosti trybar"yernykh rezonansno-tunel'nykh struktur iz postiynym elektrychnym polem

Vnesok dvofotonnykh elektronnykh perekhodiv u formuvannya aktyvnoyi dynamichnoyi providnosti trybar"yernykh rezonansno-tunel'nykh struktur iz postiynym elektrychnym polem

Thermally activated resonant tunnelling in GaAs/AlGaAs triple barrier heterostructures

We report the observation of a thermally activated resonant tunnelling feature in the current–voltage characteristics (I(V)) of triple barrier resonant tunnelling structures (TBRTS) due to the alignment of the n = 1 confined states of the two quantum wells within the active region. With great renewed interest in tunnelling structures for high frequency (THz) operation, the understanding of device transport and charge accumulation as a function of temperature is critical. With rising sample temperature, the tunnelling current of the observed low voltage resonant feature increases in magnitude showing a small negative differential resistance region which is discernible even at 293 K and is unique to multiple barrier devices. This behaviour is not observed in conventional double barrier resonant tunnelling structures where the transmission coefficient at the Fermi energy is predominantly controlled by an electric field, whereas in TBRTS it is strongly controlled by the 2D to 2D state alignment.

Resonant tunneling transport in AlzGa1−zN/InxGa1−xN/AlzGa1−zN/InyGa1−yN quantum structures

We present a room temperature simulation of the vertical electron transport in the pseudomorphic quantum stack Al0.5G0.5N/InxGa1−xN/Al0.5G0.5N/In0.1Ga0.9N/GaN, which is designed with a 6 nm thick lateral In0.1Ga0.9N/GaN n-type corrected spacer. Using the transfer matrix formalism, we investigate the effects of the conduction band discontinuities and internal field on the transmission coefficient and the current-voltage characteristics by varying the indium contents in the central quantum well. We demonstrate that an optimal design in terms of compositions, thicknesses, and doping of the studied resonant tunneling structure may allow a peak-to-valley ratio as high as 882 @1.1–1.3 V.

Nonlinear theory of the narrow-band generation and detection of terahertz radiation in resonant tunneling heterostructures

The nonlinear regime of high-frequency response for resonant tunneling structures in a time-periodic electric field has been investigated using a technique for solving the time-dependent Schrodinger equation based on a Floquet mode expansion of the wave functions. The dependences of current harmonic amplitudes on ac signal amplitude have been calculated and the limiting values of the generated field have been determined for singleand double-well resonant tunneling structures. The dynamic Stark effect is shown to play an important role in the formation of response. It leads to a quadratic (in ac field amplitude) shift in the positions of resonances Er in single-well structures and in double-well ones in the nonresonant case and to a splitting at resonance hν ≈ Er2–Er1 (ν is the signal frequency, Er1 and Er2 are the energies of the size-quantization levels) in double-well structures proportional to the ac signal amplitude. The phenomenon of ac signal detection by resonant tunneling structures has been investigated. The effect of resonant direct-current amplification in double-well structures has been detected at a signal frequency satisfying the condition hν ≈ Er2–Er1. In asymmetric systems, detection is shown to be possible in the absence of a dc bias, which allows zero-biased detectors based on them to be created.

Theory of Dynamic Conductivity of Three-Barrier Resonance-Tullel Structure with Two-Photon Laser Transitions

Within the approximation of effective mass and rectangular potential barriers for the electron and using the obtained solutions of complete Schrodinger equation, the theory of dynamic conductivity for three-barrier resonant tunneling structure (InGaAs/InAlAs) with different depths of potential wells driven by weak electromagnetic field is developed in one- and two-photon approach. 
 It is shown that varying Ga concentration one can obtain such geometric configurations of nanostructure, being an active region of quantum cascade laser, in which the increasing intensity of laser radiation, produced by electron quantum transitions accompanied by radiation of two photons with equal energy, is observed. It is established that the contribution of two-photon transitions into the complete magnitude of dynamic conductivity is not smaller than 37 %.

A Reduced-Order Method for Coherent Transport Using Green’s Functions

A reduced-order method is presented to efficiently calculate Green's functions connecting contacts or leads to all the points in a nanostructure in the coherent transport limit. The proposed approach samples a small subset of spatial grid points on the lead and a small subset of energy grid points to build a reduced-order model. The efficacy of the algorithm is demonstrated by applying it to calculate both the electron density and transmission in a resonant tunneling structure, a MOSFET, and a bilayer graphene device. The match in features of both the electron density and transmission versus energy with conventional methods to model devices is excellent while a large reduction in computational time is demonstrated.

Tunneling through a GaN/AlN-based double-barrier resonant tunneling heterostructure

The results of the fabrication and study of a double-barrier resonant tunneling structure grown on the basis of GaN and AlN wide-gap materials on a (0001)-oriented sapphire substrate are given. It is shown that, at voltages of ∼3 V, the current-voltage characteristics of resonant tunneling diode samples exhibit a region of negative differential conductivity that disappears upon multiple cyclic measurements. It is also shown that the reversal of sign of the applied voltage restores the initial shape of the current-voltage characteristics and an increase in the temperature of the structure from room temperature to 200°C yields irreversible degradation of the device and a shift of the region of negative differential conductivity to lower voltages

The impact of disorder on charge transport in three dimensional quantum dot resonant tunneling structures

Efficient iso-entropic energy filtering of electronic waves can be realized through nanostructures with three dimensional confinement, such as quantum dot resonant tunneling structures. Large-area deployment of such structures is useful for energy selective contacts but such configuration is susceptible to structural disorders. In this work, the transport properties of quantum-dot-based wide-area resonant tunneling structures, subject to realistic disorder mechanisms, are studied. Positional variations of the quantum dots are shown to reduce the resonant transmission peaks while size variations in the device are shown to reduce as well as broaden the peaks. Increased quantum dot size distribution also results in a peak shift to lower energy which is attributed to large dots dominating transmission. A decrease in barrier thickness reduces the relative peak height while the overall transmission increases dramatically due to lower “series resistance.” While any shift away from ideality can be intuitively expected to reduce the resonance peak, quantification allows better understanding of the tolerances required for fabricating structures based on resonant tunneling phenomena.

ROLE OF TWO-PHOTON ELECTRONIC TRANSITIONS IN OPERATION OF QUANTUM CASCADE LASERS

The theory of dynamic conductivity of three-barrier resonant tunneling structure in weak electromagnetic field taking into account two-photon electronic transitions with different frequencies is developed within the approximation of effective mass and rectangular potential wells and barriers for the electron using the analytically obtained solutions of complete Schrodinger equation. It is shown that the contribution of two-photon electronic transitions into the total magnitude of dynamic conductivity for some configurations of resonant tunneling structure can approach 40% for the transitions with radiation of electromagnetic wave.

Connection between bound state and tunneling problems

The transfer matrix formalism is used to show that the problem of finding the bound states of a quantum well with an arbitrary one-dimensional potential energy profile Ec(x) can be reformulated as a tunneling problem. The following theorem is proved: for an electron confined to a quantum well of size W with an arbitrary conduction band energy profile Ec(x) and maximum depth V0, the bound state energies (E1, E2, E3,…) can be found by adding a barrier of width d and height V0 on either side of the quantum well and calculating the energies at which the transmission through the resulting resonant tunneling structure reaches unity. More precisely, the energies at which the transmission coefficient reaches unity converge towards the bound state energy levels when the thickness d tends to infinity. Numerically, the bound state energies can be determined with enough accuracy by using barrier thicknesses of a few nm.

Controllable spin transport in dual-gated silicene

Abstract Based on the dual-gated silicene, we have evaluated theoretically the spin-dependent transport in lateral resonant tunneling structure. By aligning the completely valley-polarized beam with spin-resolved well state in concerned structure, large spin polarization can be expected owing to spin-dependent resonant tunneling mechanism. Under the gate electric field modulation, the forming quantum well state can be externally manipulated, triggering further the emergence of externally-controllable spin polarization. Importantly, integrating the considered structure with a proper valley-filter, which might be constructed from valley-contrasting physics as that in graphene valleytronics, completely-polarized spin beam can also be attained without the assistance of ferromagnetic component, providing thus some profitable strategies to develop nonmagnetic spintronic devices residing on silicene.

Electromagnetic Resonant Tunneling System: Double-Magnetic Barriers

We study the ballistic spin transport properties in a two-dimensional electron gas system in the presence of magnetic barriers using a transfer matrix method. We concentrate on the size-effect of the magnetic barriers parallel to a two-dimensional electron gas plane. We calculate the transmission probability of the ballistic spin transport in the magnetic barrier structure while varying the width of the magnetic barriers. It is shown that resonant tunneling oscillation is affected by the width and height of the magnetic barriers sensitively as well as by the inter-spacing of the barriers. We also consider the effect of additional electrostatic modulation on the top of the magnetic barriers, which could enhance the current spin polarization. Because all-semiconductor-based devices are free from the resistance mismatch problem, a resonant tunneling structure using the two-dimensional electron gas system with electric-magnetic modulation would play an important role in future spintronics applications. From the results here, we provide information on the physical parameters of a device to produce well-defined spin-polarized current.

On the transmission channels and current-voltage characteristics of a double-barrier nanostructure driven by dc electric and electromagnetic fields of arbitrary strength

A theory of the transmission channels and current-voltage characteristics of a double-barrier resonant tunneling structure driven by dc electric and high-frequency electromagnetic fields of arbitrary strength is proposed based on an obtained exact solution to the complete one-dimensional Schrodinger equation. It is shown for the first time that an increase in the electromagnetic-field strength leads (as a result of the formation of nonresonant transmission channels in the nanostructure) to a change in its current-voltage characteristic from a single-humped to double-humped curve not only in the vicinities of the electron-resonance energies but also in the energy ranges corresponding to the superpositions of pairs of field satellite states.

Resistance switching memory characteristics of Si/CaF2/CdF2/CaF2/Si resonant-tunneling quantum-well structures

A novel resistance switching memory scheme using Si/CaF2/CdF2/CaF2/Si resonant-tunneling quantum-well (QW) structures grown on a Si substrate has been proposed, and write-read-erase cyclic memory operation has been demonstrated by applying pulsed input voltage sequences at room temperature. A resistance switching voltage of less than 1.0 V, a peak current density of 30–72 kA/cm2, and an ON/OFF ratio of 1.9–30 were observed. Under an appropriate bias condition, a retention time of more than 315 h and cyclic pulsed operation corresponding to write-read-erase-read for more than 4500 cycles were achieved.

The effect of interface phonons on operating electron states in three-barrier resonant tunneling structure as an active region of quantum cascade detector

The Hamiltonian of electrons interacting with interface phonons in three-barrier resonant tunneling structure is established using the first principles within the models of effective mass and polarization continuum. Using the Green's functions method, the temperature shifts and decay rates of operating electron states are calculated depending on geometric design of three-barrier nano-structure GaAs/Al$_{x}$Ga$_{1-x}$As which is an active region of quantum cascade detector. It is established that independently of the temperature, the energy of quantum transition during the process of electromagnetic field absorption is a nonlinear weakly varying function of the position of the inner barrier with respect to the outer barriers of the structure.