Resonant Tunneling Effect Research Articles

Extended states and dynamical localization in semiconductor superlattices

We study the quantum dynamics of electronic wave packets in quantum-well based semiconductor superlattices subject to an applied electric field. Using a high-accuracy numerical method, we analyze the dynamical behavior of electronic wave packets in periodic, random and random dimer superlattices. The spatial extent of electronic states is characterized by means of the time-dependent inverse participation ratio. We show that the delocalized states recently found in random dimer superlattices become spatially localized under the action of the applied field (dynamical localization) but wavepackets are much less localized than in purely random superlattices at moderate field. We conclude that the resonant tunneling effects causing delocalization in dimer superlattices play an important role even in the presence of moderate electric field.

Resonant tunneling effect of quantum well-superconductor junction

In this paper a semiconductor double barrier-quantum well-superconductor (DBQS) junction is proposed and the I–V characteristics was obtained by employing a generalized Giaever formula and Andreev reflection method. The result shows that the I–V curve of DBQS junction exhibits negative differential resistance. It is suggested that this effect can be used to fabricate a new electronic device.

Experimental demonstration of single peak IV characteristics in a novel resonant tunneling diode

Single peak IV characteristics are experimentally demonstrated by a novel resonant tunneling diode, a resonant tunneling pinch-off diode (RTPD), specially designed to make the coupling between the pinch-off effect and the resonant tunneling effect in the diode itself effective. RTPDs were fabricated using the InGaAs-AlAs-InAlAs material system grown by MBE on semi-insulating InP substrate. Device parameter (emitter width and collector thickness) dependence of the IV characteristics is investigated and compared with previously reported theory. Good agreement between them confirms that the mechanism that brings about the novel characteristics in the RTPD is the above mentioned coupling, and gives guidelines for achieving an RTPD with ideal single peak IV characteristics.

Resonant macroscopic quantum tunneling in SQUID systems: Theoretical fitting of experimental data

A theoretical model for the effects of resonant macroscopic quantum tunneling in SQUID systems is presented. This allows us to make for the first time a comparison of theory with experiment.

Interference effects in resonant tunneling and the Pauli principle

A new method is proposed for studying resonant tunneling in semiconductor heterostructures. The method manifestly takes account of electron statistics, which enables one to investigate the influence of the Pauli principle on resonant tunneling in coupled quantum wells. It is shown that the interplay of the Pauli exclusion principle with coherent resonant tunneling results in a peculiar behavior of the resonant current, very different from that derived in the one-electron picture.

Electron transfer between two coupled quantum wells in a resonant tunneling diode structure

Resonant tunneling effects between the quantum well of a double barrier heterostructure and the accumulation layer of the emitter region are investigated. Numerous singularities in the current-voltage characteristic of a GaAs Al 0.4Ga 0.6As diode, such as a negative differential conductance effect with a current contrast of 15:1, have been found and analyzed by means of self-consistent calculations of conduction band profile and tunneling probabilities. At relatively low bias, charge transfer can be interpreted as direct or scattering-assisted transitions with optical phonon emission, by considering the anti-crossing of the ground states or the energy conservation rules. At higher voltages, very fast tunneling processes at the time scale of relaxation mechanisms (through the second level of the accumulation layer) were demonstrated. Such a hot electron transition with direct evidence of negative differential conductance effect involves a non expected build-up of the resonance as a function of the symmetry of confining potentials in terms of transmission probabilities.

Resonant tunneling effect through a parabolic quantum well

We present a theoretical investigation on the resonant tunneling effect in an AlAs double-barrier structure with a AlGaAs central well having a special parabolic geometry. The results are similar to those obtained in a transverse resonant magnetotunneling experiment (with a magnetic field parallel to the interfaces of a square well).

Resonant tunneling single electron transistors

We use a modulation-doped double barrier heterostructure to fabricate a resonant tunneling single electron transistor. Irregular Coulomb blockade oscillations are observed when the gate voltage is swept to vary one-by-one the number of electrons in the dot close to 'pinch-off'. The oscillation period is not regular, and generally becomes longer as the electron number is decreased down to zero, reflecting the growing importance of electron-electron interactions and size quantization. Negative differential resistance associated with resonant tunneling through zero-dimensional states is pronounced for a dot holding just a few electrons. The temperature dependence of the Coulomb blockade oscillations and that for the negative differential resistance are not the same. This highlights the different effects of charging and resonant tunneling on the transport characteristics.

Proposal and analysis of resonant tunnellingdiode with single peaked I-V characteristics

A novel resonant tunnelling diode with single peaked I-V characteristics is proposed. In this diode, the resonant tunnelling effect in a vertical double barrier structure is coupled with the pinch-off effect in a lateral collector just beneath the structure. Using a one-dimensional distributed parameter model, the dependence of the I-V characteristics on the device parameters (emitter width and collector thickness) is investigated systematically.

Effect of temperature on the resonant macroscopic quantum tunneling in small Josephson junctions

The study of the quantum behaviour of Josephson junctions is interesting not only by itself, but also for the technological importance in electronics employing superconducting weak links. Recently great attention has been devoted to the effects of Resonant Macroscopic Quantum Tunneling (RMQT) between levels the same energy in neighbouring wells of the potential shape describing the junction. This can produce voltage spikes along the supercurrent branch of the I-V curves and peaks in the current switching distributions. Schmidt, Clealand, and Clarke have presented a detailed analysis of the resonant tunnel dynamics for the T=0 case. The present paper is based on a different theoretical approach, first proposed by Larkin and Ovchinnikov, which allows one to include explicitly the temperature. We study the phenomenon in its time dependence and this allows us to consider the lifetime of the voltage spikes as well as the effect of the RMQT on the quantum escape rate out of the V=0 state.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Characteristics of a GaAs-InGaAs quantum-well resonant-tunneling switch

A switching device, with a p-type delta-doped sheet in the center of an InGaAs-GaAs quantum well, has been fabricated and demonstrated. An N-shaped negative-differential-resistance phenomenon resulting from the resonant-tunneling effect through the miniband is observed in the current-voltage measurement. From the experimental results, it is seen that the temperature plays an important role in device operation. The influences of temperature upon the peak-current voltage, valley-current voltage, peak-current density, and valley-current density are studied and discussed.

Time-dependent transport in interacting and noninteracting resonant-tunneling systems

We consider a mesoscopic region coupled to two leads under the influence of external timedependent voltages. The time dependence is coupled to source and drain contacts, the gates controlling the tunnel-barrier heights, or to the gates that define the mesoscopic region. We derive, with the Keldysh nonequilibrium-Green-function technique, a formal expression for the fully nonlinear, time-dependent current through the system. The analysis admits arbitary interactions in the mesoscopic region, but the leads are treated as noninteracting. For proportionate coupling to the leads, the time-averaged current is simply the integral between the chemical potentials of the time-averaged density of states, weighted by the coupling to the leads, in close analogy to the time-independent result of Meir and Wingreen [Phys. Rev. Lett. 68, 2512 (1992)]. Analytical and numerical results for the exactly solvable noninteracting resonant-tunneling system are presented. Due to the coherence between the leads and the resonant site, the current does not follow the driving signal adiabatically: a "ringing" current is found as a response to a voltage pulse, and a complex time dependence results in the case of harmonic driving voltages. We also establish a connection to recent linear-response calculations, and to earlier studies of electron-phonon scattering effects in resonant tunneling.

Modifications in the Si valence band after ion-beam-induced oxidation

The changes undergone by the Si surface after oxygen bombardment have special interest for acquiring a good understanding of the Si+-ion emission during secondary ion mass spectrometry (SIMS) analysis. For this reason a detailed investigation on the stoichiometry of the builtup surface oxides has been carried out using in situ x-ray photoemission spectroscopy (XPS). The XPS analysis of the Si 2p core level indicates a strong presence of suboxide chemical states when bombarding at angles of incidence larger than 30°. In this work a special emphasis on the analysis and interpretation of the valence band region was made. Since the surface stoichiometry or degree of oxidation varies with the angle of incidence, the respective valence band structures also differ. A comparison with experimentally measured and theoretically derived Si valence band and SiO2 valence band suggests that the new valence bands are formed by a combination of these two. This arises from the fact that Si–Si bonds are present on the Si-suboxide molecules, and therefore the corresponding 3p–3p Si-like subband, which extends towards the Si Fermi level, forms the top of the respective new valence bands. Small variations in intensity and energy position for this subband have drastic implications on the intensity of the Si+-ion emission during sputtering in SIMS measurements. A model combining chemically enhanced emission and resonant tunneling effects is suggested for the variations observed in ion emission during O+2 bombardment for Si targets.

GaAs-InGaAs quantum-well resonant-tunneling switching device grown by molecular beam epitaxy

In this letter, a new switching device having a p-type delta-doped sheet in the center of an InGaAs-GaAs quantum well is presented. An N-shaped negative-differential-resistance (NDR) phenomenon resulting from the resonant tunneling effect through the miniband under a proper anode-to-cathode voltage is observed. From the experimental results, it is seen that the temperature plays an important role in the device operation.

Resonant tunneling and charging effects in semiconductor quantum dots

The current in the stationary state through an interacting island coupled to several reservoirs is investigated. Recent discussions about the occurence of Pauli-blocking factors are clarified and a generalization of the linear-response theory of Coulomb-oscillations and cotunneling is presented for many-level quantum dots at low temperatures. A strong influence of repeated cotunneling processes on the resonant line shape is obtained.

Anomalous conductivity phenomenon and quantum size effects in a new microstructure-modulated superlattice

Quantum size effects such as the modulation of activation energy have been observed and investigated in hydrogenated microcrystalline silicon (μc-Si:H)/hydrogenated amorphous silicon (a-Si:H) microstructure-modulated superlattices. The longitudinal dark conductivity changes anomalously around a temperature in the temperature dependence of the longitudinal dark conductivity for these superlattices. Studies indicate that these superlattices exhibit negative resistance above room temperature. We owe the anomalous conductivity phenomenon to the multibarrier resonant tunneling through the μc-Si:H/a-Si:H multiple-quantum-well structure. By considering the resonant tunneling effects, the anomalous conductivity behavior can be successfully explained.

Exciton effects in sequential resonant tunneling of photocarriers in GaAs/AlAs multiple quantum wells.

We have studied the sequential resonant tunneling characteristics of coupled GaAs/AlAs quantum wells (QW's) by measuring the electric-field dependence of the photocurrent and of the excitonic photoluminescence (PL) associated with the first and second conduction subband. If the first subband of a QW is resonantly aligned with the second subband of the adjacent QW, a maximum of the photocurrent, a strong reduction of the PL intensity from the first subband, and a pronounced enhancement of the PL associated with the second subband are observed. Unexpectedly, these resonant extrema are observed at different electric fields. This phenomenon is attributed to the different binding energies of the intrawell and interwell excitons.

The role of phase-breaking processes in indirect-band tunneling barrier structures

A new description of the observed resonant tunneling effect in single barrier III–V structures are presented, based on inelastic or phase-breaking scattering. Near the interfaces in a GaAs/AlAs/GaAs quantum structure there is a substantial spatial overlap between Γ and X states of the GaAs and the AlAs regions, respectively. As a result, the X band in the AlAs barrier layer provides regions of enhanced current-carrying energy states into which Γ band electrons can scatter through phase-breaking scattering. In this description, scattered electrons are reinjected into states belonging either to Γ or X bands at rates determined by respective density of states.

Electrical characteristics of a stacked nitride/microcrystalline-silicon/oxide/silicon structure

This letter reports a stacked nitride/microcrystalline-silicon/oxide/silicon structure, which exhibits a higher electron injection efficiency, a less electron trapping rate, and a larger charge to breakdown than the normal oxide. Besides, the room-temperature resonant tunneling effect is also observed for this structure.

On the possibility of a mode selector and its application to quantum devices

A mode selector is proposed to realize single modedness in the waveguidelike quantum devices. The mode selecting function is theoretically demonstrated by the principle of resonant tunneling effect. Its applications to quantum field-effect directional couplers and three-port devices are also theoretically studied. The result shows that the mode selector can considerably improve device function by suppressing the mode correlation in the device.