Space charge dynamics in a semiconductor superlattice affected by titled magnetic field and heating

The transition between different modes of current oscillations in a semiconductor superlattice, from close-to-harmonic (near the generation onset) to relaxation oscillations, has been investigated. The transition type is shown to change with an increase in temperature. A period-doubling bifurcation is observed at low temperatures. With an increase in temperature, the period-doubling bifurcation is observed at increasingly larger values of the voltage across the superlattice. The doubling bifurcation ceases to be observed at voltages at which the generation of oscillations of the current through the semiconductor superlattice is suppressed.     

The effect of temperature on the nonlinear dynamics of charge in a semiconductor superlattice in the presence of a magnetic field

The space-time dynamics of electron domains in a semiconductor superlattice is studied in a tilted magnetic field with regard to the effect of temperature. It is shown that an increase in temperature substantially changes the space-time dynamics of the system. This leads to a decrease in the frequency and amplitude of oscillations of a current flowing through the semiconductor superlattice. The quenching of oscillations is observed, which is attributed to the change in the drift velocity as a function of electric-field strength under the variation of temperature.     

Effect of the fraction of semiconducting inclusions on the properties of self-sustained oscillations in a metal-semiconductor system

A model of self-sustained oscillations in a heterophase system consisting of metal and semiconductor layers is constructed. It is shown that parameters of self-sustained oscillations (amplitude and period) can be controlled by varying the fraction of metal inclusions in the semiconductor. The numerical solution of the system of equations for the heterophase system shows that, the higher the temperature coefficient of resistance of the metal, the stronger the effect of the metal impurity on the properties of the heterophase system, manifested in a decrease in the effective band gap and in suppression of self-sustained oscillations.     

Conductance Oscillations in Spin Field-Effect Transistors

Ballistic spin transport in spin field-effect transistors is studied by taking into account the Rashba spinorbit coupling, interracial scattering, and band mismatch. It is shown that the spin conductance oscillation with the semiconductor channel length is a superimposition of the Rashba spin precession and spin interference oscillations. They have different oscillation periods π/κR and π/κ with κR the Rashba wavevector and κ the Fermi wavevector of the semiconductor channel, and play different parts of slow and rapid oscillations, depending upon the relative magnitude of π/κR and π/κ. Only at κ = κR does the spin conductance exhibit oscillations of a single period. Two types of different behaviors of the tunnelling magnetoresistance are discussed.     

Synchronization of chaotic semiconductor lasers by optical injection with random phase modulation

It is shown that identical synchronization of two chaotic semiconductor lasers can be achieved by injection of a common optical signal with randomly varying phase. An optical signal with randomly modulated phase is injected into two semiconductor lasers which have chaotic oscillations due to optical feedback. Strong correlation between complex intensity oscillations of the two lasers is observed even though the intensity of the common injection signal is constant. Characteristic properties of this type of synchronization are shown, in particular, the dependence of the synchronization threshold on the injection strength and the rate of phase modulation, and the dependence of the intensity correlation on the difference in phase of optical feedback.     

Electromagnetic waves and oscillations in the layered semiconductor-dielectric-semiconductor structure

Theoretical and numerical studies of the electromagnetic properties of the layered semiconductor — dielectric — semiconductor (SDS) structure was carried out. It was shown that the weak damping guide and surface waves may exist in this structure and retardation of surface waves may be several times more than for the semiconductor — dielectric (SD) interface. If this structure contains reflections it leads to the formation of high Q-factor resonance oscillations. It was found that at the beginning of intermode coupling of two surface oscillations in the studied resonance structure, hybrid surface oscillations with near resonance frequencies are formed. Their electromagnetic field components along the wave propagation direction are orthogonal to each other and modulated along the SD interface by orthogonal envelopes.     

Spin-dependent shot noise in diluted magnetic semiconductor/semiconductor heterostructures with a nonmagnetic barrier

We investigate quantum size effect on the spin-dependent shot noise in the diluted magnetic semiconductor (DMS)/semiconductor heterostructure with a nonmagnetic semiconductor (NMS) barrier in the presence of external magnetic and electric fields. The results demonstrate that the NMS barrier plays a quite different role from the DMS layer in the electron transport process. It is found that spin-down shot noise shows relatively regular oscillations as the width of DMS layer increases, while the spin-up shot noise deceases monotonically. However, as the width of NMS layer increases, the spin-down shot noise displays irregular oscillations at first and then decreases while the spin-up shot noise decreases at a quite different rate. The results indicate that the shot noise can be used as a sensitive probe in detecting material type and its size.     

Dynamics of a filtered-feedback laser: influence of the filter width

The behavior of a semiconductor laser subject to filtered optical feedback is studied in dependence on the width of the filter. Of special interest are pure frequency oscillations where the laser intensity is practically constant. We show that frequency oscillations are stable in a large region of intermediate values of the filter width, where the dispersion of the filter is able to compensate for the well-known phase-amplitude coupling of the semiconductor laser. Our stability diagram covers the entire range from a very narrow filter, when the system behaves like a laser with monochromatic optical injection, to a very broad filter, when the laser effectively receives conventional (i.e., unfiltered) optical feedback.     

Plasmon-interband coupling in gallium compounds

Electro energy loss spectra have been measured for metallic Ga and the semiconductor compounds GaSb, GaAs, GaP and GaN. The intensity at the measured plasmon energy decreases with increasing ionicity of the compound semiconductor. This is explained by a simple model involving the coupling of plasmon oscillations and interband transitions.     

Acoustic analogue of electronic BLOCH oscillations and resonant Zener tunneling in ultrasonic superlattices

We demonstrate the existence of Bloch oscillations of acoustic fields in sound propagation through a superlattice of water cavities and layers of methyl methacrylate. To obtain the acoustic equivalent of a Wannier-Stark ladder, we employ a set of cavities with different thicknesses. Bloch oscillations are observed as time-resolved oscillations of transmission in a direct analogy to electronic Bloch oscillations in biased semiconductor superlattices. Moreover, for a particular gradient of cavity thicknesses, an overlap of two acoustic minibands occurs, which results in resonant Zener-like transmission enhancement.     

Optical detection of the Aharonov-Bohm effect on a charged particle in a nanoscale quantum ring

We study spectroscopically the current produced by a charged particle moving in a nanosize semiconductor quantum ring subject to a perpendicular magnetic field. Several Aharonov-Bohm oscillations are observed in the emission of a charged exciton confined in a single ring structure. The magnetic field period of the oscillations correlates well with the size of the rings.     

Quantum corrections to the conductivity and periodic orbits: Integrable systems

We extend the recently developed semiclassical theory for the conductivity to periodic semiconductor structures whose classical dynamics is integrable. We find that the conductivity of integrable systems exhibits quantum oscillations as function of magnetic field and Fermi energy which are closely related to both the Shubnikov-de Haas oscillations and the oscillations observed in the conductivity of antidot lattices. A general expression for the quantum oscillations is derived which is analogous to the Berry-Tabor formula for the spectral density of integrable systems.     

Short period magnetic coupling oscillations in Co/Si multilayers: Theory versus experiment

Today the magnetic properties of multilayers and nanostructures including a metal or an insulator as a nonmagnetic spacer layer are rather well understood. But they are much more controversial for semiconductor spacers. For instance, for Co/Si multilayers short period coupling oscillations are predicted by ab initio computations but have yet to be observed. Here we show in Co/Si multilayers prepared at low temperature (90 K) strong saturation field oscillations that are consistent with the predicted coupling oscillations. However, the decay length of the oscillations is much longer than the expected one and cannot be explained within the framework of available theories.     

Self-sustained oscillations in a low-current discharge with a semiconductor serving as a cathode and ballast resistor: I. Experiment

Self-sustained current oscillations in a Townsend discharge that is excited in a short plane discharge gap and is uniform along the electrode surface are investigated experimentally. A thin semiconductor plane serves as a discharge cathode, a ballast resistor, and an additional capacitor in the dc power supply circuit. The domain of existence and the frequency and waveform of oscillations are determined over a wide pressure range.     

Oscillations of the free electron concentration in a semiconductor under the action of a femtosecond pulse

The interaction of a femtosecond light pulse with a semiconductor is studied in the approximation of an optically thin layer taking into account the dependence of the absorption coefficient on the light-induced electric field. A possibility of the development of spatial oscillations of semiconductor characteristics (concentrations of free electrons and ionized donors and the strength of the light-induced electric field) under the action of a Gaussian beam is demonstrated on the basis of computer simulation and linear analysis.     

Experimental synchronization of chaotic oscillations in external-cavity semiconductor lasers

Synchronization of fast chaotic oscillations of the order of gigahertz is experimentally observed in two external-cavity semiconductor lasers.     

Thermodynamic functions of electron gas on the semiconductor nanotube surface in a magnetic field

Thermodynamic functions have been calculated in the effective mass approximation for degenerate and nondegenerate electron gases on the semiconductor cylindrical nanotube surface in a longitudinal magnetic field. The Laplace transform linking the density of states and the statistical sum has been used. The thermodynamic quantities of degenerate electron gas undergo the de Haas-van Alphen oscillations with the electron Fermi energy change and the Aharonov-Bohm oscillations with the magnetic flux change within the semiconductor tube cross section. The quantities related to nondegenerate gas oscillate only with the change of magnetic flux. A peak has been found in the nondegenerate gas heat capacity-temperature diagram. A limiting process to 2D electron gas on plane has been carried out.     

Observation of low-frequency fluctuations in vertical-cavity surface-emitting lasers

Low-frequency fluctuations, which are typical irregular oscillations in edge-emitting semiconductor lasers, are experimentally observed for the y-polarization mode (y is the direction along the optical axis of a laser material) in a vertical-cavity surface-emitting laser with optical feedback.     

外光注入半导体激光器实现时钟分频

从理论和实验上研究了利用光注入半导体激光器对高重复速率光脉冲产生的周期振荡和时钟分频现象.结果表明，光注入半导体激光器引起的二倍周期振荡是使注入脉冲重复频率分频的直接原因.通过耦合速率方程，数值模拟了半导体激光器在外光注入时输出光的时间序列和功率谱，并且分析了激光腔内各种周期振荡的特征.研究表明，当注入光使半导体激光器出现稳定的二倍周期振荡，且注入光的重复频率为此振荡频率的二倍时，时钟分频即可产生实验中，采用重复频率为6.32GHz的光脉冲注入Fabry-Perot激光器，实现了3.16GHz时钟分频信号 关键词： 周期振荡 时钟分频 光谱侧带 光注入     

Evolution of entanglement between distinguishable light states

We investigate the evolution of quantum correlations over the lifetime of a multiphoton state. Measurements reveal time-dependent oscillations of the entanglement fidelity for photon pairs created by a single semiconductor quantum dot. The oscillations are attributed to the phase acquired in the intermediate, nondegenerate, exciton-photon state and are consistent with simulations. We conclude that emission of photon pairs by a typical quantum dot with finite polarization splitting is in fact entangled in a time-evolving state, and not classically correlated as previously regarded.