Lateral surface magnetoplasma modes of type II semiconductor superlattices

The recently developed theory of superlattice lateral surface magnetoplasmon is extended to type II superlattices consisting of alternating two-dimensional planes of electrons and holes. The magnetoplasmon dispersion relation is calculated by transforming the two coupled integral equations for the a.c. potential into a composite matrix equation. This method can be generalized to study charge density collective excitations in an arbitrary multi-component superlattice.     

Investigation of an AlInAs/GaInAs superlattice-emitter resonant tunneling bipolar transistor (SE-RTBT)

A new bipolar transistor with a 20-period i-AlInAs/n⁺-InGaAs superlattice, prepared by metal organic chemical vapour deposition, has been fabricated and demonstrated. This superlattice is used as a confinement barrier for holes and a resonant tunneling (RT) route for electrons. Due to the RT effect within the 20-period superlattice near emitter–base p–n junction region, the N-shaped negative-differential-resistance (NDR) phenomena are observed under normal operation. A transistor action with a common-emitter current gain of 13 and a small offset voltage (90 mV) is achieved at room temperature.     

Stark states in semiconductor quantum wells and superlattices

The quasi-bound states of electrons and holes in coupled GaAsAlGaAs quantum wells in the presence of an applied electric field perpendicular to the wells are determined by the exact solution of the Schroedinger equation using the iteration matrix formalism. The transmission probability in a finite superlattice is also calculated taking into account the exact wave functions in the barriers and wells. The method can be useful to interpret recent tunneling-current measurements.     

Nonlinear Electronic Transport Equations for Tunneling Superlattices

We present a nonlinear electronic transport theory for a tunneling superlattice which is composed of interacting electrons with impurity and phonon scatterings. The theory is based on the Lei-Ting balance-equation method and a newly developed matrix separation technique for the density-correlation-function. Taking account of the overlap of the wave-functions between adjacent wells, the nonlinear dc resistivity in a transverse strong electric field is explicitly expressed in terms of the matrixdensity- correlation-function, which can be straightforwardly calculated in RPA as long as the single well wave function is given.     

The variably spaced superlattice energy filter

A new superlattice device concept which provides for high energy injection of electrons into a semiconductor layer is presented. The device is based on resonant tunneling of electrons between adjacent aligned quantum well levels in a variably spaced superlattice structure. By a judicial choice of well and barrier widths the energy levels under reverse bias become aligned such that resonant tunneling of electrons through the structure can occur. Thus, electrons are injected into a semiconductor layer at an energy corresponding to the energy of the first subband in the last quantum well. This structure has significant advantages over the conventional method of producing hot electrons in that a nearly monoenergetic high-energy electron distribution is created at low reverse bias and with high efficiency, since energy loss to phonons is inhibited as a consequence of the channeling of electrons through a narrow band of quantum states. Applications of the VSSEF structure to avalanche photodiodes, IMPATT diodes and electroluminescent devices are discussed.     

超导邻近效应在正常金属层中引起的反常小能隙现象

将散射矩阵方法推广到超导双结系统，对正常金属/正常金属/超导结的隧道电导进行了研究.中间正常金属层中的电子和其Andreev反射空穴之间的相位相干性导致了隧道电导出现反常小能隙现象.综合考虑相干和顺序遂穿，计算结果理想的解释了最近Gupta等人在实验中观测到的反常小能隙现象.     

Intraminiband plasmons in a superlattice within a parabolic well

A well defined collective plasma resonance corresponding to electrons tunneling back and forth through superlattice barriers is observed in a series of modulation doped AlGaAs heterostructures containing a superlattice within a parabolic potential. Due to occupation of a large fraction of the miniband, the resonance frequency decreases strongly with increasing superlattice barrier thickness.     

Excitonic Effect on the Electron Tunneling Through a Quant urn Well

We proposed a simplified model to describe the excitonic effect on electron tunneling through a quantum well (QW). Using nonequilibrium-Green-function method self consistently, we calculated the dc current of electron tunneling through QW. The extra plateau in the J-V characteristics appears dearly, which shows the existence of exciton in QW. This result is in good agreement with the experiment qualitatively. We also studied the density of electrons and holes in the quantum well.     

Bloch electrons in a magnetic field: Topology of quantum states and transport

Quantum states and Hall conductances of electrons in n-type heterojunctions and holes in p-type heterojunctions in a field of a lateral superlattice and a perpendicular magnetic field were studied. It is shown that the energy spectrum of magnetic subbands in a periodic potential without inversion center is not symmetric about the reversal of the quasi-momentum sign. The properties of wave functions and the related topological invariants determining the Hall conductance were examined. The method of calculating the magnetic Bloch states of holes was developed on the basis of the Luttinger Hamiltonian, allowing the spin and spin-orbit interactions to be taken into account in this problem. The Hall conductance quantization law was determined for 2D holes in a periodic superlattice potential.     

Quantum tunnel reflectors and superlattices on their basis

A dispersion relation ε (q) is derived for electrons in a planar superlattice constructed in the form of a quantum well that is coupled by tunneling with a periodic array of parallel strip-shaped quantum wires. A narrow miniband inside of the substantially wider gap is demonstrated for special resonance conditions. Since the obtained spectra are very sensitive to correlation of different array parameters they can be tuned and detuned easily.     

Properties of excitons in a wide CdTe-based quantum well with irregular insertions of a fractional monolayer of ZnTe

The irregular short period CdTe/ZnTe superlattice structure is investigated by both stationary and time-resolved optical spectroscopy with and without an external magnetic field as a perturbation. This study is aimed to emphasize the properties of radiative excitonic recombination in a superlattice of this type in comparison with the excitons confined in a single QW structure. The decay time of the excitons is about 400 ps which is deduced from the time-resolved measurements. Theg-factors of electrons and holes are obtained by the spin quantum beat measurements combined with Zeeman measurements. The experimental results show that theg-factors of holes in the irregular short period CdTe/ZnTe superlattice become dramatically different in comparison with the single CdTe/CdMgTe quantum wells.     

Relaxation time for a charge carrier due to its scattering from other charge carriers in superlattices

A calculation of relaxation time for (i) electron–electron scattering in a modulation-doped superlattice of type-I and (ii) electron–electron, hole–hole and electron–hole scattering processes in a compositional superlattice of type-II has been performed, using Fermi's golden rule. As compared to a two-dimensional electron gas system, both intralayer and interlayer interactions, between charge carriers in a superlattice, contribute to relaxation time. It is found that scattering processes at all possible value of momentum transfer contribute to relaxation time, for a given value of temperature and carrier density. We further find interlayer interactions in a superlattice make a significant contribution to relaxation time. Relaxation time is found to decrease on increasing temperature, carrier density and single particle energy, in a superlattice. The computed relaxation time for an electron (hole) in a superlattice enhances on increasing the width of layer consisting of electrons (holes). The electron–hole (hole–electron) scattering process in a type-II superlattice yields maximum contribution to the relaxation time when a hole layer lies exactly in between two consecutive electron layers.     

Temperature effects of GaAs/Al_(0.45)Ga_(0.55)As superlattices on chaotic oscillation

For widespectrum chaotic oscillation, superlattice cryptography is an autonomous controllable brand-new technology.Originating from sequential resonance tunneling of electrons, the chaotic oscillation is susceptible to temperature change,which determines the performance of superlattices. In this paper, the temperature effects of chaotic oscillations are investigated by analyzing the randomness of a sequence at different temperatures and explained with superlattice microstates.The results show that the bias voltage at different temperatures makes spontaneous chaotic oscillations vary. With the temperature of superlattices changing, the sequence dives in entropy value and randomness at specific bias. This work fills the gap in the study of temperature stability and promotes superlattice cryptography for practice.     

Phase coherence of the electron and hole in a ferromagnetic film in proximity with a superconductor

The scattering matrix approach between the clean and dirty limits is developed for the study of tunneling spectra in a ferromagnetic film in proximity to a superconductor. The minigap and the damped oscillation from ``0" to ``π" state in tunneling conductance are attributed to the phase coherence of the electrons and the corresponding Andreev-reflected holes in the ferromagnetic film. The calculated results provide a reasonable explanation for the behavior observed in recent experiments.     

Error diagrams and temporal correlations in a fracture model with characteristic and power-law distributed avalanches

The field-induced carrier redistribution between the subbands of a semiconductor superlattice is treated using the density matrix approach. The unit cell of the superlattice consists of one quantum well with three occupied subbands. Carrier scattering on polar-optical phonons is described within the microscopic bulk phonon model. At the tunneling resonance, an intrinsic population inversion is observed. The temperature dependence of the population inversion is determined. Received 25 October 2002 / Received in final form 27 November 2002 Published online 6 March 2003 RID="a" ID="a"e-mail: kl@pdi-berlin.de     

Two-dimensional electron gas in double quantum wells with tilted bands

When a voltage is applied to double quantum wells based on AlGaAs/GaAs heterostructures with contact regions (n-i-n structures), a two-dimensional (2D) electron gas appears in one of the quantum wells. Under illumination which generates electron-hole pairs, the photoexcited holes become localized in a neighboring quantum well and recombine radiatively with the 2D electrons (tunneling recombination through the barrier). The appearance, ground-state energy, and density of the degenerate 2D electron gas are determined from the structure of the Landau levels in the luminescence and luminescence excitation spectra as well as from the oscillations of the radiative recombination intensity in a magnetic field with detection directly at the Fermi level. The electron density is regulated by the voltage between the contact regions and increases with the slope of the bands. For a fixed slope of the bands the 2D-electron density has an upper limit determined by the resonance tunneling of electrons into a neighboring quantum well and subsequent direct recombination with photoexcited holes. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 11, 840–845 (10 June 1997)     

Thermal dissociation of excitons in a type-I GaAs/AlAs superlattice studied by time-resolved photoluminescence measurements

In order to investigate thermal properties of excitons, we have performed time-resolved photoluminescence (PL) measurements for a type-I (GaAs)₁₅/(AlAs)₁₅ superlattice. At low temperatures, PL signals show ordinal exponential time decay, whereas at high temperatures, the PL shows power decay. Such change of PL signals is understood by considering thermal dissociation of exciton into account. At low temperatures, recombination of bound excitons generates PL which shows exponential decay. At temperatures higher than the exciton binding energy, correlation between electrons and holes disappears. Recombination of free excitons causes PL which decays by a power function. By means of the least-squares fitting, we evaluate the portion of bound excitons, recombination time of bound and free excitons as functions of temperatures.     

Creation of an atomic superlattice by immersing metallic adatoms in a two-dimensional electron sea

Cerium adatoms, deposited on a Ag(111) surface, are found by low-temperature scanning tunneling microscopy to self-assemble into large ordered hexagonal arrays covering macroscopically the entire surface. We show that the 32 A periodicity of the superlattice is caused by the interaction of surface-state electrons with Ce adatoms and that the large-scale formation of the superlattice is governed by a subtle balance between the sample temperature, the surface diffusion barrier, and the concentration-dependent adatom interaction potential.