Double Barrier Resonant Tunneling Research Articles

Coherent tunneling in a semiconductor system: Double barrier resonant-tunneling structure built in the Schottky barrier

Resonant-tunneling processesing electrons in a system consisting of the double-barrier resonanttunneling structure built in the Schottky barrier are studied. It is shown that the coherent tunneling can take place in this system; both the transmission rates of electrons and the current-voltage characteristic are evaluated and analyzed for such a case. The theoretical results agree perfectly well with the data obtained from the especially performed experiment.

Switching behaviour and high frequency response of amorphous carbon double-barrier structures

In order to produce fast memory switching devices fabrication of double-barrier resonant tunnel diodes (DB-RTD) based on amorphous semiconductors with a prominent signature of resonant tunnelling and negative differential resistance (NDR) was attempted. We have developed DB-RTDs of amorphous carbon and showed unique features including NDR peaks, quantized conductance and switching effects in these structures. From the analysis of these experimental data the effective mass of electron of about 0.07 times the free electron mass, a high value of mobility and long coherence length of electrons in this low dimensional disordered system is derived. At higher operational bias voltage we recorded periodic current steps, which are explained by the creation of 1D channels in this structure. These features suggest ballistic conduction. We are able to tune the switching characteristics of these structures in the presence of microwave frequency at about 100 GHz which resembles a quantum well capacitor with a fast relaxation time. The increase of conductance at a particular bias, in the presence of microwave frequency can be explained through an increase of mobility and increased relaxation time of electrons. A carbon-based memory suitable for very fast operation, compared to other organic polymer systems is suggested.

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.

Negative differential resistance in dislocation-free GaN∕AlGaN double-barrier diodes grown on bulk GaN

Double-barrier GaN resonant tunneling diodes with AlGaN barriers were fabricated on bulk (0001) single-crystal GaN substrates. Layers were grown using molecular-beam epitaxy with a rf plasma nitrogen source. Single diodes of 6μm diameter were prepared by inductively coupled plasma reactive ion etching. For many diodes clear negative differential resistance is observed around 2V with peak currents around 10kA∕cm2 and a peak-to-valley ratio of about 2 at room temperature. Its observation does not depend on specific conditions of measurement; however, it slowly decays after each measurement. The mechanism behind this decay is investigated since it is obviously prohibiting the usage of GaN resonant tunneling diodes so far. It is shown not to be caused by catastrophic breakdown of the devices.

Current–voltage characteristics in double-barrier resonant tunneling diodes with embedded GaAs quantum rings

Abstract We report current–voltage ( I – V ) characteristics in GaAs/AlGaAs double-barrier resonant tunneling diodes (DB-RTDs), in which GaAs quantum rings (QRs) that are grown on a 4-nm thick GaAs are sandwiched between AlGaAs barrier layers. The QRs prepared by droplet epitaxy are 40 nm wide and 4 nm high. Negative differential resistance (NDR) and asymmetric resonance feature are observed in the QR-embedded RTDs. From comparison with references, we conclude that the NDR feature is originated from the 4-nm thick QW, not QRs.

Decay of metastable current states in one-dimensional resonant tunneling devices

Current switching in a double-barrier resonant tunneling structure is studied in the regime where the current-voltage characteristic exhibits intrinsic bistability, so that in a certain range of bias two different steady states of current are possible. Near the upper boundary V_{th} of the bistable region the upper current state is metastable, and because of the shot noise it eventually decays to the stable lower current state. We find the time of this switching process in strip-shaped devices, with the width small compared to the length. As the bias V is tuned away from the boundary value V_{th} of the bistable region, the mean switching time \tau increases exponentially. We show that in long strips \ln\tau \propto (V_{th} -V)^{5/4}, whereas in short strips \ln\tau \propto (V_{th} -V)^{3/2}. The one-dimensional geometry of the problem enables us to obtain analytically exact expressions for both the exponential and the prefactor of \tau. Furthermore, we show that, depending on the parameters of the system, the switching can be initiated either inside the strip, or at its ends.

Delayed feedback control of stochastic spatiotemporal dynamics in a resonant tunneling diode

The influence of time-delayed feedback upon the spatiotemporal current density patterns is investigated in a model of a semiconductor nanostructure, namely a double-barrier resonant tunneling diode. The parameters are chosen below the Hopf bifurcation, where the only stable state of the system is a spatially inhomogeneous "filamentary" steady state. The addition of weak Gaussian white noise to the system gives rise to spatially inhomogeneous self-sustained temporal oscillations that can be quite coherent. We show that applying a time-delayed feedback can either increase or decrease the regularity of the noise-induced dynamics in this spatially extended system. Using linear stability analysis, we can explain these effects, depending on the length of the delay interval. Furthermore, we study the influence of this additional control term upon the deterministic behavior of the system, which can change significantly depending on the choice of parameters.

Current–Voltage Characteristics of γ-Al2O3/epi-Si Resonant Tunneling Diodes with Different Quantum Well Thicknesses

The fabrication of double-barrier resonant tunneling diodes (DBRTDs) using γ-Al2O3/epitaxial-Si heterostructures with different well thicknesses and different barrier thicknesses was studied. Current–voltage characteristics of the DBRTDs were investigated to determine the relationships between the peak-to-valley current ratio and the quantum well thickness, and between the peak current density and the barrier thickness for the maximum peak-to-valley current ratio (PVCR) at room temperature. In this study, we confirmed a maximum peak-to-valley current ratio of 26 at room temperature with a quantum well (epi-Si) thickness of 3 nm and a barrier (γ-Al2O3) thickness of 2 nm. A comparison between the theoretical and experimental peak voltage positions for a negative differential resistance was performed, indicating good agreement. A lower peak current density of few mA/cm2 was obtained.

Carbon string structures: First-principles calculations of quantum conductance

Carbon forms various nanostructures based on the monatomic chains or strings which show transport properties of fundamental and technological interest. We have carried out first-principles quantum conductance calculations using optimized structures within density functional theory. We treated finite segments of carbon monatomic chain, metal-semiconductor heterostructure, and resonant tunneling double barrier formed of C-BN chains, as well as symmetric and antisymmetric loop devices between two electrodes. We examined the effects of electrode, contact geometry, size of the device, strain, and foreign atoms adsorbed on the chain. Calculated quantum ballistic conductance of carbon chains showing even-odd disparity depending on the number of atoms and strain are of particular interest. Notably, chains consisting of an even number of carbon atoms contacted to metal electrodes display a resonant tunneling-like behavior under axial strain. The double covalent bonding of carbon atoms depicted through self-consistent charge density analysis underlies unusual transport properties.

On double barrier quantum well conductance effects due to exchange and correlation

AbstractConductance investigations in double barrier resonant tunneling (DBRT) structures under an applied voltage usually make use of the BenDaniel–Duke equation (BDK), coupled to the Poisson equation, to incorporate electron interactions through the Hartree term in a self‐consistent way. By including an extra self‐consistency condition, it is possible to go beyond the Hartree approximation and include exchange and correlation (EC) effects through the local density approximation (LDA). In this paper, the inclusion of EC effects is made by means of the analytically parametrized υinf xc of Hedin and Lundqvist. A comparison with previous work that excludes such effects is carried out for the energy spectrum as well as for the field dependent conductance in a GaAs/AlGaAs DBRT structure. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Monolithic AlAs-InGaAs-InGaP-GaAs HRT-FETS with PVCR of 960 at 300 K

This letter reports the significant N-shaped negative-differential resistance characteristics with three-terminal controllability of a monolithic heterostructure resonant tunneling field-effect transistor, realized by integrating the AlAs-In/sub 0.25/Ga/sub 0.75/As-AlAs double-barrier single-well resonant tunneling (RT) structure into the drain regime of the In/sub 0.49/Ga/sub 0.51/P-In/sub 0.25/Ga/sub 0.75/As-GaAs /spl delta/-high-electron mobility transistor. A peak-to-valley current ratio in excess of 960 at room temperature has been demonstrated, with a peak current density (J/sub p/) of 50.6 mA/mm, and a valley current density (J/sub v/) of 52.7 μA/mm, respectively, with a transistor gate length of 1.0 μm. The maximum current drive density was observed to be 478 A/mm-cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> .

Reply to “Comment on ‘Lifetime of metastable states in resonant tunneling structures’ ”

The authors of the Comment 1 on our earlier paper 2 estimate the critical size of the initial nucleus of the low-current state in a double-barrier resonant tunneling structure sDBRTSd. Their estimate is based on the theory of deterministic switching front propagation. They claim that for realistic parameters of DBRTS, the size of the critical nucleus rcr is comparable with the sample size. Even when rcr is smaller than the size of the sample, it is still macroscopic and, therefore, is too large for the switching to occur, as the switching time should increase exponentially with the area of the nucleus. They subsequently conclude that the decay of the metastable state via the nucleation mechanism is doubtful. The conclusion that rcr is macroscopically large is based on the numerical estimate rather than on physical argument. Therefore, we first discuss this numerical estimate and then give our physical estimate for r cr . The authors of the Comment define the macroscopic size as “e.g., .10 mm.” They claim that r cr is given by the front width W, which is found using the theory of deterministic switching front propagation. This theory describes the deterministic growth of the nucleus of the new phase well after the critical size has been reached. On the other hand, the formation of the critical nucleus is not deterministic, but a stochastic process that we considered in our paper. 2 At the formation stage the theory of switching front propagation can be expected to provide an order of magnitude estimate for rcr such as Eq. s2d in the Comment. Under certain assumptions this estimate can be reproduced from the theory of stochastic switching 2 ssee belowd.

Wave packet approach to periodically driven scattering

For autonomous systems it is well known how to extract tunneling probabilities from wave packet calculations. Here we present a corresponding approach for periodically time-dependent Hamiltonians, valid at all frequencies, field strengths, and transition orders. After mapping the periodically driven system onto a time-independent one with an additional degree of freedom use is made of the correlation function formulation of scattering [D. J. Tannor and D. E. Weeks, J. Chem. Phys. 98, 3884 (1993)]. The formalism is then applied to study the transmission properties of a resonant tunneling double barrier structure under the influence of a sinusoidal laser field, revealing an unexpected antiresonance in the zero-photon transition for large field strengths.

Kinetic theory of quantum transport at the nanoscale

We present a quantum-kinetic scheme for the calculation of non-equilibrium transport properties in nanoscale systems. The approach is based on a Liouville-master equation for a reduced density operator and represents a generalization of the well-known Boltzmann kinetic equation. The system, subject to an external electromotive force, is described using periodic boundary conditions. We demonstrate the feasibility of the approach by applying it to a double-barrier resonant tunneling structure.

Solid-phase diffusion mechanism for GaAs nanowire growth.

Controllable production of nanometre-sized structures is an important field of research, and synthesis of one-dimensional objects, such as nanowires, is a rapidly expanding area with numerous applications, for example, in electronics, photonics, biology and medicine. Nanoscale electronic devices created inside nanowires, such as p-n junctions, were reported ten years ago. More recently, hetero-structure devices with clear quantum-mechanical behaviour have been reported, for example the double-barrier resonant tunnelling diode and the single-electron transistor. The generally accepted theory of semiconductor nanowire growth is the vapour-liquid-solid (VLS) growth mechanism, based on growth from a liquid metal seed particle. In this letter we suggest the existence of a growth regime quite different from VLS. We show that this new growth regime is based on a solid-phase diffusion mechanism of a single component through a gold seed particle, as shown by in situ heating experiments of GaAs nanowires in a transmission electron microscope, and supported by highly resolved chemical analysis and finite element calculations of the mass transport and composition profiles.

Resonant thermal transport in semiconductor barrier structures

I report that thermal single-barrier (TSB) and thermal double-barrier (TDB) structures (formed, for example, by inserting one or two regions of a few Ge monolayers in Si) provide both a suppression of the phonon transport as well as a resonant-thermal-transport effect. I show that high-frequency phonons can experience a traditional double-barrier resonant tunneling in the TDB structures while the formation of Fabry-Perot resonances (at lower frequencies) causes quantum oscillations in the temperature variation of both the TSB and TDB thermal conductances ${\ensuremath{\sigma}}_{\mathrm{TSB}}$ and ${\ensuremath{\sigma}}_{\mathrm{TDB}}.$

Quantum dot infrared photodetector design based on double-barrier resonant tunnelling

A novel quantum dot infrared photodetector design, based on double-barrier resonant tunnelling, is proposed and demonstrated. Theoretical calculations predict significantly lower dark currents in this device, compared to conventional quantum dot photodetectors. This is borne out of experimental results.

Fabrication of resonant-tunneling diodes by Sb surfactant modified growth of Si films on CaF/sub 2/Si

Molecular beam epitaxy growth of Si thin films on CaF/sub 2//Si(111) substrates has been studied. A surfactant-modified solid-phase epitaxy method, where the room temperature Si deposition was followed by annealing under Sb flux, resulted in a continuous, smooth epitaxial crystalline Si film with a sharp (/spl radic/3/spl times//spl radic/3)R30/spl deg/ reconstruction and a surface roughness of 0.15-nm rms for a 2.8-nm Si thin film. This growth technique was used to fabricate CaF/sub 2//Si/CaF/sub 2/ double-barrier resonant tunneling diodes in SiO/sub 2/ windows patterned on Si(111) substrates. A negative differential resistance (NDR) peak was found at /spl sim/0.35 V at 77 K, and the current density at the NDR peak was estimated to be 3-4 orders of magnitude higher than in earlier reports.

Creation and quenching of interference-induced emitter-quantum wells within double-barrier tunneling structures

The initial creation and subsequent quenching of the emitter quantum well within double-barrier resonant tunneling structures (RTSs) is the key process that explains the origin of the hysteresis and plateau-like structure of the I–V characteristics. This fundamental process, which evolves out of quantum-mechanical interference, defines the basic mechanism that can lead to intrinsic high-frequency oscillations. This article presents numerical results, derived from a coupled Wigner–Poisson model, that illustrate the underlying mechanisms responsible for the creation and disappearance of the emitter-quantum well. Additional theoretical results are also given that demonstrates how subband state coupling, between the emitter-quantum well (EQW) and the main-quantum well (MQW) defined by the double-barrier heterostructure, leads to the hysteresis and instability behavior. This article will reveal how the quantum interference that develops between the incident and reflected electron wave function (i.e., from the first barrier) leads to the formation of an emitter-quantum well. An analysis is also performed to define the effects of EQW–MQW subband coupling on the current–density verses voltage (I–V) characteristics and the overall I–V dependence on the initial charging states of the individual wells. In particular, this analysis is used to show how the EQW is formed and quenched and how it influences the time-dependent behavior of the structure when it is subject to forward- and backward-bias sweeps of the applied bias voltages. This article provides fundamental quantum-mechanical explanations for the complicated time-dependent processes within double-barrier RTSs and provides insight into the hysteresis and intrinsic oscillation behavior.

Resonant magnetotunneling of photogenerated holes in double barrier structures

In this work, we report on a technique—namely, the photoinduced magnetotunneling technique—which allows the direct experimental observation of tunneling of holes through valence-band Landau levels in n-i-n double-barrier resonant tunneling structures. Photocurrent–voltage curves exhibit several peaks associated with the complex nature of the dispersion of holes under parallel electric and magnetic fields applied to the sample.