Double Barrier Resonant Tunneling Structures Research Articles

Coherent electron quantum transport in hbox {In}_{0.53}hbox {Ga}_{0.47}As/GaAs_{0.51}hbox {Sb}_{0.49} double barrier resonant tunnelling structures

In this work, we have modelled and computed the transport properties of the double-barrier InGaAs/GaAsSb structure from the resonant tunnelling point of view. Based on the classical Tsu-Esaki formula for the tunnelling current, we have calculated the current density-voltage characteristic of a Al-free type-II hbox {In}_{0.53}hbox {Ga}_{0.47}hbox {As/GaAs}_{0.51}hbox {Sb}_{0.49} structure at different cryogenic and elevated temperatures. The tunnelling coefficient has been calculated in the framework of effective mass approximation with nonparabolicity included, using the transfer matrix approach. A good qualitative agreement of the position of resonant current peaks with the existing experimental data was achieved. Our calculation shows a very high sensitivity of the tunnelling current peak on monolayer-scale layer structure fluctuation which strongly affects peak to valley ratio in the resonant tunnelling structure.

Electronic Transport and Resonant Tunneling Properties of Hyperbolic Pöschl-Teller Double-Barrier Structures

The ballistic electron transport characteristics of hyperbolic Pöschl-Teller double-barrier resonant tunneling structures are investigated. The transmission coefficient and the current density-voltage characteristic in electrically biased one dimensional hyperbolic Pöschl-Teller double-barrier structures with different structure parameters have been calculated by using non-equilibrium Green’s function method. Results for the transmission coefficients and the current densities are compared with the barrier shapes. The results show that the widths of the wells and heights of barriers have a significant effect on the transmission properties. The current density-voltage characteristic presents N-type negative differential resistance.

Potential of HfN, ZrN, and TiH as hot carrier absorber and Al2O3/Ge quantum well/Al2O3 and Al2O3/PbS quantum dots/Al2O3 as energy selective contacts

The hot carrier (HC) solar cell is one of the most promising advanced photovoltaic concepts. It aims to minimise two major losses in single junction solar cells due to sub-band gap loss and thermalisation of above band gap photons by using a small bandgap absorber, and, importantly, collecting the photo-generated carriers before they thermalise. In this paper we will present recent development of the two critical components of the HC solar cell, i.e., the absorber and energy selective contacts (ESCs). For absorber, fabrication and carrier cooling rates in potential bulk materials — hafnium nitride, zirconium nitride, and titanium hydride are presented. Results of ESCs employing double barrier resonant tunneling structures Al2O3/Ge quantum well (QW)/Al2O3 and Al2O3/PbS quantum dots (QDs)/Al2O3 are also presented. These results are expected to guide further development of practical HC solar cell devices.

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.

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

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.

Transmission Canals for the Photon-Assisted Transport of Electron through the Double-Barrier Resonant Tunneling Structure

The resonance and non-resonance transmission canals of double-barrier resonant tunneling structure are established for the electron photon system using the exact solution of one-dimensional non-stationary Schrodinger equation expanded into the Fourier range. It is shown that besides the main and satellite, the mixed quasi-stationary states which cause the appearance of speci c transmission canals with the properties strongly dependent on the intensity and frequency of electromagnetic eld, exist in the nanostructure.

Spin-dependent tunneling transport in a lateral magnetic diode

Based on the gate-tunable two-dimensional electron gas, we have constructed laterally a double-barrier resonant tunneling structure by employing a peculiar triple-gate configuration, namely a ferromagnetic gate sandwiched closely by a pair of Schottky gates. Because of the in-plane stray field of ferromagnetic gate, the resulting bound spin state in well gives rise to the remarkable resonant spin polarization following the spin-dependent resonant tunneling regime. Importantly, by aligning the bound spin state through surface gate-voltage configuration, this resonant spin polarization can be externally manipulated, showing the desirable features for the spin-logic device applications.

Repeatable low-temperature negative-differential resistance from Al0.18Ga0.82N/GaN resonant tunneling diodes grown by molecular-beam epitaxy on free-standing GaN substrates

Low-aluminum composition AlGaN/GaN double-barrier resonant tunneling structures were grown by plasma-assisted molecular-beam-epitaxy on free-standing c-plane GaN substrates grown by hydride-vapor phase epitaxy. Clear, exactly reproducible, negative-differential resistance signatures were observed from 4 × 4 μm2 devices at 1.5 V and 1.7 V at 77 K. The relatively small value of the maximum peak-to-valley ratio (1.03) and the area dependence of the electrical characteristics suggest that charge transport is affected by leakage paths through dislocations. However, the reproducibility of the data indicates that electrical traps play no significant role in the charge transport in resonant tunneling diodes grown by molecular-beam-epitaxy under Ga-rich conditions on free-standing GaN substrates.

Tunneling Properties in GaAs/Al<sub>0.33</sub>Ga<sub>0.67</sub>As/In<sub>x</sub>Ga<sub>1-x</sub>As Double-Barrier Resonant Tunneling Structures

We study the tunneling properties in GaAs/Al0.33Ga0.67As/InxGa1-xAs (x=0~0.05) double-barrier resonant tunneling structures. On increasing bias voltage, the behavior of current density for x=0 can be explained by the interplay between the increase of the supply function of available electrons and the decrease of transmission coefficient through device area. On increasing the Indium content from 0, the peak current density decreases, and the reason is that both the supply function and the transmission coefficient decreases. At zero bias, the structure is on resonance with the lowest x value of 0.02.

Simulation of GaAs/Al<sub>x</sub>Ga<sub>1-x</sub>As/In<sub>y</sub>Ga<sub>1-y </sub>As Double-Barrier Resonant Tunneling Structures

We study the resonant tunneling in symmetric GaAs/AlxGa1-xAs/InyGa1-yAs double-barrier resonant-tunneling structures. Effects of three factors on the resonant tunneling are simulated and discussed. On increasing the barrier height, the decrease of current density is attributed to the interplay between the increase of the supply function of available electrons and the rapid decrease of the transmission coefficient through the device area, and the lowest Indium content for realizing the zero-bias resonant tunneling increases. With the increase of the barrier (well) width, the decrease of the current density can be explained by the fact that both the supply function and the transmission coefficient decreases, and the lowest Indium content meeting the zero-bias resonant condition decreases.

Phase-breaking effects in double-barrier resonant tunneling diodes with spin-orbit interaction

Several recent theoretical studies showed that the spin-orbit interaction in narrow gap InGaAs/InAlAs double-barrier resonant tunneling structures might yield a highly spin-polarized current in the ballistic limit. In this paper, a nonequilibrium Green’s function model is used to examine the effect of phase-breaking on the spin-dependent transport of carriers. The scattering is described as a local interaction with a bath of scatterers and treated in the self-consistent first Born approximation. Elastic and inelastic scatterers, with scattering strengths that cause a few millielectron volt broadening of quasibound states, have been found to significantly reduce the spin polarization. The magnitude of spin polarization has been found to be dominantly determined by the quasibound state broadening, while the interaction details are not significant.

Resonant Tunneling in III-Nitrides

Wide-bandgap semiconductors can sustain high temperatures and high power operation in various important applications such as transistors, light-emitting diodes, and lasers. Although in embryonic stage, one can expect such a resilience in GaN resonant tunneling diodes (RTDs) and superlattices as well with distinct applications. Because of the negative differential conduction, the double barrier resonant tunneling structures could be the basis for new high-power coherent microwave sources operating in W-band and terahertz. In this paper, recent progress in wide-bandgap semiconductor RTDs is discussed.

A quantum transport model for the double-barrier nonmagnetic spin filter

A model for calculating the current and spin polarization in a double-barrier InGaAs resonant tunnelling structure is described with the aim to account for phase-breaking scattering. It is based on the nonequilibrium Green's function method with both elastic and inelastic (LO-phonon) scattering described within the self-consistent first Born approximation. It has been found that the maximum current spin polarization of around 0.4 in the ballistic limit decreases to around 0.1 for scattering transport with scattering-induced broadening of quasi-bound states of around 4meV.

Energy selective contacts for hot carrier solar cells

Double barrier resonant tunnelling structures consisting of silicon quantum dots (QDs) in silicon dioxide ( SiO 2 ) matrix have been studied for Energy Selective Contacts for Hot Carrier solar cell. A single layer of silicon QDs has been fabricated by high temperature annealing of SiO 2 / Si-rich oxide (SRO)/ SiO 2 layers deposited by RF magnetron sputtering. Compositional analysis of SRO films obtained with different sputtering target has been accurately measured with Rutherford backscattering spectroscopy. Size-controlled growth of Si QDs has been studied with photoluminescence measurements which demonstrate that QD sizes can be controlled with SRO layer thickness. In addition, resonant tunnelling behaviour of SiO 2 / Si QD/ SiO 2 structures has been investigated.

Spin-polarization in InAs/AlSb double barrier resonant tunneling structures: influence of barrier material and interface structure

We present a study on the atomistic simulation of the spin-polarized transmissions through InAs/AlSb double barrier resonant tunneling heterostructures. By making use of the atomistic sp3s* tight binding Hamiltonian including the intra-atomic spin-orbit interaction and the recursive Green’s function method, we obtain the significant anisotropic zero-magnetic-field spinsplitting of the resonant transmission peak in the absence of the external electric field, demonstrating the importance of the barrier material and the atomic scale detail of the hetero interfaces on the spin-splitting.

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.

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.

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

A New Resonant Tunnelling Structure of Integrated InGaAs/GaAsVery-Long-Wavelength Quantum-Well Infrared Photodetector

We perform a theoretical study on a low dark current InGaAs/GaAsvery-long-wavelength (>12 μm) quantum well infraredphotodetector (VLW-QWIP), based on a double barrier resonant tunnellingstructure (DBRTS). The ground tunnelling state of the central quantumwell (QW) of the DBRTS can resonate with the first excited bound stateof the doped InGaAs QW by adjusting the structure parameters of theDBRTS. Investigation of the carrier transport performance of this deviceis carried out based on quantum wave transport theory. It has beenshown that the dark current in this device can be significantly reducedby two orders compared to conventional InGaAs/GaAs VLW-QWIPs, while thephotocurrent is almost the same as those in conventional VLW-QWIPs.This DBRTS integrated VLW-QWIP structure may stimulate the experimentalinvestigation for VLW-QWIPs at high operation temperatures.